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UNDERSTANDING SOLAR TERRESTRIAL REPORTS
PART II - INTERPRETING THE REPORTS
REVISION 1.2
_A_B_S_T_R_A_C_T
Part I of this document discussed the morphology of
solar and geophysical phenomena. With this background now
in hand, a discussion of the solar terrestrial reports
themselves can begin. The purpose of this document is to
explain the meaning of the various sections of the Solar
Terrestrial Forecast and Review which are posted over the
networks on a weekly basis. In addition, the purpose and
application of the other reports, alerts and warnings will
be discussed. After having digested the material in parts
I and II of this document, the interested reader should
have enough background and knowledge to begin actively
applying the information in the reports. The reader is
encouraged to digest part I of this document first (Part I
- Morphological Analysis of Phenomena). It may be
obtained upon request from "oler@hg.uleth.ca".
July 14, 1991
UNDERSTANDING SOLAR TERRESTRIAL REPORTS
PART II - INTERPRETING THE REPORTS
REVISION 1.2
_1. _I_n_t_r_o_d_u_c_t_i_o_n
The solar terrestrial reports posted over the networks presently
consist of several reports, alerts and warnings. The Solar Terres-
trial Forecast and Review is the only regular weekly publication. It
contains a summary of conditions which occurred over the preceding
week and includes forecasts for the next 10 to 20 days. This report
is the one which will be concentrated on most heavily in part II of
this document. It contains most of the data, forecasts and charts
required and used in practical applications.
The Major Solar Flare Warning is a brief message which is posted
over the nets when a major flare (or flares) may be possible. These
messages are only sent when regions on the solar surface are complex
and threatening enough to produce potentially major energetic
activity. They are therefore only intended to alert people to the
increased potential for major flare activity.
A Major Flare Alert is posted whenever a major energetic flare
erupts on the sun (of class M5.0 or greater). Such an alert include a
description of the event and any outstanding accompanying phenomena
(ex. sweep frequency events, abnormally high radio bursts, etc.). If
the flare could have a terrestrial impact, an impact assessment is
given within the body of the alert message.
The Major Geomagnetic Storm Alert is posted whenever geomagnetic
conditions reach storm levels over middle latitudes. These alerts are
not posted when storm conditions may exist for high latitudes, because
high latitudes experience a significantly greater number of magnetic
storms than do the lower latitudes and fewer numbers of people are
affected by the high latitude storm periods than middle latitude
storms.
We begin our discussion of the solar terrestrial reports with an
analysis of the solar terrestrial review section of the reports. We
will attempt to cover the language used and discuss the format of this
section of the reports. Following this, we will continue with a dis-
cussion of the Monthly Solar Terrestrial Review followed by a discus-
sion of the Geomagnetic Storm Alerts. The Major Solar Flare alerts
and warnings should be more easily understood after this document has
been digested.
The interested reader may need to re-read parts I and II of this
document before aquiring a clearer understanding of these reports and
their applications. A great deal of material is covered in this
July 14, 1991
- 2 -
document and may not be fully understood the first time through.
Application of these reports to the various inter-related fields may
require practice and persistence in order to understand the impacts of
certain events on specific terrestrial systems (such as radio communi-
cations). The interested reader is encouraged to do personal research
on the subjects of solar activity, ionospheric properties, radio pro-
pagation and geophysical activity. Research in these areas will sig-
nificantly enhance ones understanding and ability to interpret and
apply the information contained in the publicized reports, alerts and
warnings.
_2. _T_h_e _S_o_l_a_r _T_e_r_r_e_s_t_r_i_a_l _F_o_r_e_c_a_s_t _a_n_d _R_e_v_i_e_w
This report is the primary report of solar and geophysical
activity. It includes enough information and data to be of use to
many people involved in radio communications, solar physics and geo-
physics. It is issued once a week and contains summaries and fore-
casts for the next 10 to 20 days.
The report itself is compiled from raw data obtained from several
sources. One of the major sources is the Space Environment Services
Center (SESC), which serves as a major global data-collection center
for space-related environmental data. The SESC is responsible for the
solar terrestrial information which is posted on radio stations WWV
and WWVH at 18 minutes past each hour.
The data obtained from the various sources are all collected and
analyzed by before being compiled into the reports which are publi-
cally posted. Computer models, coronal maps and recurrent patterns
are all examined and analyzed. The results are incorporated into the
various forecasts in the reports. The actual prediction methods are
beyond the scope of this paper.
In this section, we will begin a systematic analysis of the vari-
ous sections of the Solar Terrestrial Forecast and Review. Some of
the terms contained herein may not be clearly defined. For those
terms which are unclear, the interested reader is encouraged to con-
sult the "Glossary of Solar Terrestrial Terms", available upon request
from "oler@hg.uleth.ca".
_2._1. _S_u_m_m_a_r_y _o_f _S_o_l_a_r _T_e_r_r_e_s_t_r_i_a_l _A_c_t_i_v_i_t_y
This section of the report summarizes the highlights of solar and
geomagnetic activity which took place over the preceeding week. Solar
activity is given first, followed by a summary of geomagnetic and
auroral activity. Following this, a summary of the HF and VHF propa-
gation conditions for the preceeding week are given. Any particularly
severe solar or terrestrial activity will be given special treatment
in this section.
Basically, the summary of solar activity includes a discussion of
those regions on the sun which exhibited abnormal signs of activity.
July 14, 1991
- 3 -
This may include a description of major solar flares, noteworthy fila-
ment disappearances, or unusually large coronal holes. It may also
include a description of various unusual or impressive forms of limb-
activity such as prominences, plage or faculae activity, or limb
surges or flares.
In all of the solar summaries, references will be made to
specific regions postfixed with specific numbers (ie. Region 6354).
These "region numbers" are simply sequential numbers assigned to
active regions as they appear or are identified. The numbering of
these regions was started by the SESC many years ago. The first
region to be assigned was given a region number of 1. Consecutively
identified regions were given numbers of 2, 3, 4 and so on. Each new
region is given the next consecutive region number.
In order for a region to be assigned a region number, it must
qualify according to one of the following criteria: (1) If the region
has a sunspot group which has a first-postion type-classification of
C, D, E, F or H, it will be given a region number (see the "Glossary
of Solar Terrestrial Terms for a description of the sunspot classifi-
cation scheme). (2) If two or more reports confirm the presence of
class A or B spots (again, see the above-referenced document), it will
be given a region number. (3) If the region produces a solar flare,
it will be given a region number. (4) If the region is "bright" in
H-alpha light and exceeds 5 heliographic degrees in either latitude or
longitude, it will be given a region number. These four criteria are
used in determining what areas are assigned solar region numbers by
the SESC and which areas are not.
The vast majority of solar summaries include statements regarding
the intensity (or class) of specific flare events. Flares are
categorized using two types of classifications. The first method
categorizes a flare with regards to its output energy at X-ray
wavelengths measured by orbiting satellites. The second method
categorizes flares according to their size and brightness at optical
wavelengths (observed using monochromatic H-alpha light filters).
Both of these flare classifications are described fully in the "Glos-
sary of Solar Terrestrial Terms." Refer to it for more information.
The positions of all solar regions and events are given according
to the format: AxxByy, where xx represents a latitude (in degrees),
"A" represents either the "N" (North) or "S" (South) solar hemisphere,
"yy" represents the solar longitude given in degrees east or west of
the central solar meridian, and "B" represents either "E" (East) or
"W" (West) of this central meridian (ex. N26E72). The exact center of
the visible sun represents the origin where the longitude is measured
from. The extreme limbs of the solar disk represent longitudes of 90
degrees (either East or West, depending on which limb you look at),
while the extreme poles of the sun represent 90 degrees latitude
(either North or South, again depending on which hemisphere is
observed).
It should be noted that the orbit of the earth carries us
slightly above and below the suns rotational equator. During six
July 14, 1991
- 4 -
months of the year, we are above the northern portion of the solar
equator, while during the next six months, we fall below the southern
portion of the solar equator. Near the equinoctial periods (spring
and fall), our orbit places us at our maximum distance above or below
the solar equator. If, at these times of the year, the earth were
moved in a straight line toward the center of the sun, the earth would
make contact with the suns surface at a latitude of about 7.3 degrees
with respect to the solar equator. Although these periods do not
exactly coincide with the each equinox (ie. maximum southerly extent
is achieved on 07 March, while maximum northerly extent is reached on
09 September), they do coincide within a month of the equinox.
These latitudinal changes are important, since it alters the way
we must observe the sun. During the equinox periods, the center of
the sun as we see it is actually about 7 degrees to the north or south
of the actual solar equator. If this were not taken into account, the
measured positions of sunspots and other surface features would be
grossly in error.
The important point to remember when studying the positions of
sunspot groups is that the coordinates given represent the position of
the sunspots relative to the rotation axis of the sun as viewed from
earth. For example, a sunspot group located at a position of N21E62
represents a position 21 degrees north of the solar equator, and 62
degrees east of the solar central meridian (or 28 degrees away from
the eastern limb [ 90 - 62 = 28 ]).
Since the sun rotates from east to west, all sunspot groups and
other observed features rotate in the same direction. More specifi-
cally, the sunspots rotate at an average speed of about 13 degrees per
day. So the sunspot group located at N21E62 would be located at
N21E49 the following day, and N21E36 the day after that. They may
also occasionally drift in latitude, although the drift in latitude is
negligable most of the time.
Following the solar summary, the summary for geophysical and
auroral activity is presented. These summaries should be mostly
self-explanatory with the exception of possible notes regarding mag-
netic fluctuations.
In summaries of particularly intense magnetic activity, state-
ments may be made regarding the maximum intensity of some of the mag-
netic fluctuations observed during the period being reviewed. These
summaries will generally involve the terms _n_a_n_o_t_e_s_l_a and/or _g_a_m_m_a,
which are synonymous. The intensity of magnetic fluctuations are
latitude-dependent. Higher latitudes naturally experience more
intense magnetic fluctuations than the lower latitudes. Southerly
middle latitude regions consider magnetic fluctuations of 500
nanotesla (_n_T) to be very severe, while high latitudes may consider
fluctuations of 2500 nT to be very severe. The magnetic A and K
indices have been developed to aid in equating the intensity of mag-
netic fluctuations over wide latitudes. For example, a magnetic fluc-
tuation at Anchorage Alaska may be considered to be as "equally
intense" as a similar fluctuation in California if the A or K-indices
July 14, 1991
- 5 -
for both locations are equal, even though the actual magnitude of the
fluctuations at Anchorage are much higher than the corresponding fluc-
tuations in California. A K-index of 4 at Yellowknife in northern
Canada may correspond to a magnetic fluctuation of 160 nT, while a K-
index value of 4 at Boulder Colorado may correspond to an actual mag-
netic fluctuation of only 50 nT. Both fluctuations may be considered
_e_q_u_a_l_l_y _s_e_v_e_r_e based on how often fluctuations of that magnitude are
usually encountered for that latitude. Yellowknife may encounter
fluctuations of 50 nT on a daily basis whereas Boulder may not
encounter magnetic fluctuations of that magnitude for weeks. Hence
the need for indices which can equalize the latitudinal dependencies.
Notes of auroral activity in the review section of the report are
generally limited to descriptions as described in the Glossary of
Solar Terrestrial Terms. However, for extraordinary events such as
occur during auroral storms, a more detailed examination of auroral
activity may be given. Such descriptions may include auroral types,
color fluctuations, pulsations or movement patterns of auroral forms.
All of these descriptions are contained in the Glossary mentioned
above and part I of this document.
Notes regarding HF and VHF propagation are usually confined to
brief accounts of overall global conditions. These conditions are
generally rated as either above normal, normal, below normal or very
poor. Above normal propagation indicates strong signals which are
abnormally stable. Above normal propagation is most often associated
with good to very good DX potentials. Normal propagation denotes nor-
mal conditions after considering the season and the position within
the sunspot cycle. It is compared with the average conditions experi-
enced over previous seasons and solar cycles. Below normal propaga-
tion is usually associated with increased geomagnetic activity and is
more consistent with signals of lower quality, less stability, and
weaker strengths. Chances for DX drop noticably during periods of
below normal propagation, except for the VHF bands where an increase
in DX may actually occur. Very poor propagation is most often associ-
ated with magnetic storms or PCA events where signal absorption, fad-
ing and instability dramatically affect the quality of signals. Dur-
ing intense storms, localized _b_l_a_c_k_o_u_t conditions may occur. This
term may be used in these instances to denote exceedingly high signal
absorption levels. Again, the exception is VHF frequencies, where
long-distance communications often improves during periods of high HF
absorption or blackout periods. However, the quality of the VHF sig-
nals may be quite poor despite the enhanced communication range.
_2._2. _S_h_o_r_t _T_e_r_m _S_o_l_a_r _T_e_r_r_e_s_t_r_i_a_l _F_o_r_e_c_a_s_t
This section of the report follows the same basic structure as
the review described in the last section, except that predictions are
given instead of reviews. The predictions are made using the same
methods described in the preceding sections, but are translated from
tables and charts into sentence form.
This short-term prediction section is intended to point out the
highlights which can be expected over the coming week. Overall global
July 14, 1991
- 6 -
conditions are given in this section of the report. Therefore, the
person interested in radio communications or auroral activity should
keep in mind the nature of this section. It is not intended to list
the possible localized phenomena which might occur. Just the general
overall global conditions are stated.
The short term forecasts should be used as a guide only. The art
of predicting geomagnetic storms and major flares is by no means an
easy process. There are many variables which are unknown and
processes which are not fully understood yet. Although we have made
great advancements in the fields of solar physics and geophysics, we
have a long way to go in the area of predictions. The forecasts
presented in these reports may therefore be in error at times. They
are, however, based on the most current models and the most recent
data.
_2._3. _S_o_l_a_r _R_e_g_i_o_n _S_u_m_m_a_r_y
The summary of solar regions is the section of the report which
is in tabular form and includes the region numbers, sunspot sizes,
sunspot classes, angular extents, magnetic configuration, etc. This
section is of great value to those who are tracking sunspot groups or
watching for signs of growth or increased magnetic complexity and/or
flaring.
Although each of the aspects of this table are described in the
Glossary of Solar Terrestrial Terms, we will elaborate on some of the
more vague terms of in this section.
Each solar region is given a number and its position on the solar
disk is measured (as was described above). This identifies and
defines the exact position of a solar region on the sun. The posi-
tional description (ie. the latitude/longitude description) is rela-
tive to the hemisphere of the sun which is in view. That is, the
longitude of a solar region is relative to the center of rotation as
seen from the earth. This places the 00 degree longitude (ie. the
central meridian) continuously at the center of the sun (in a line
stretching from the north solar pole through the center of the disk as
observed from the earth, to the south solar pole). All of the solar
regions rotate while the longitudinal lines remain stationary. This
method of marking positions of sunspots and other phenomena is very
adequate, but fails to describe the position of sunspots on a solar
global basis with respect to a fixed 360 degree longitudinal system
(as is employed for the Earth).
In order to solve this problem, a system was developed to begin
mapping active regions on a fixed solar geographical basis. The
actual longitudinal position of sunspots are therefore recorded in two
different ways. The first way (described in the preceding sections)
enables us to determine how far away a solar region is from the cen-
tral meridian. It effectively separates the observable solar disk
into an east and a west hemisphere with the dividing line coinciding
with the central solar meridian. The second method is analagous to
the way we have mapped the Earth, with fixed lines of longitude
July 14, 1991
- 7 -
dividing up the entire sphere.
The figures in the region summary under the heading "_L_O"
represent this second mapping method. This second method is useful in
determining the movement of a sunspot region compared to the flow of
gases around the sunspot region. Sometimes, sunspots will move
slightly slower than the gases around the spot, which will gradually
cause the longitudinal location of the sunspot to change. Sometimes,
they move faster than the gases normally do at that location. So by
observing these longitudinal values, you can determine whether a sun-
spot is moving faster or slower than usual.
This method of referencing sunspots is also useful in identifying
regions of the sun which are abnormally active. During the years of
maximum solar activity, the sun often exhibits longitudinal regions
which are more active than other longitudes. During solar maximum
years, there are often two areas of abnormal activity separated by
about 180 degrees. By observing the positions of sunspots using this
method of mapping, the active solar longitudes can be discovered.
This is valuable for those who want to forecast solar activity. Like-
wise, some solar longitudes are often regions of enhanced corpuscular
emissions (ie. regions where matter is ejected from the sun), which
can significantly affect radio communications and geomagnetic
activity. Plotting the positions of these active longitudes can also
be of tremendous aid in predicting recurrent storms or periods of
increased geophysical activity.
The column in the table labelled "_Z" represents an optical clas-
sification scheme for sunspots and sunspot groups. The details of
this classification method are given in the Glossary of Solar Terres-
trial Terms. The interested reader is directed to consult this docu-
ment for more information. It categorizes the optical shape and com-
plexity of sunspot groups.
The column labelled "_L_L" represents the angular extent of the
sunspot group. Angular extent is given in solar degrees. Comparing
this value with the number of spots within the region (denoted by the
"_N_N" column of the table) yields the density of the group. The den-
sity is important because it is an indirect measure of the gradients
of magnetic fields within the region. High gradients produce more
frequent and more severe solar flares, while weak gradients are usu-
ally associated with less-compact spot groups which produce less
severe and less frequent flares.
The "_M_A_G _T_Y_P_E" or magnetic-type of sunspot groups as noted in the
last column of the table can also be used to determine the magnetic
complexity and magnetic gradients within active regions. Consult the
Glossary mentioned above for more information regarding these classif-
ications.
In addition to details on spot groups, this region of the report
also enumerates those areas which are _n_o_t associated with sunspots,
but contain areas of enhanced H-alpha plages. These regions are
assigned region numbers according to the rules noted above. These
July 14, 1991
- 8 -
regions are often the sites for sunspot formation. They may also be
associated with old regions which are decaying.
_2._4. _G_e_o_m_a_g_n_e_t_i_c _A_c_t_i_v_i_t_y _S_u_m_m_a_r_y
Following the solar region summary, a graphical analysis of
recent geomagnetic activity is presented. This graphical table charts
planetary geomagnetic activity as it is recorded for many magnetic
observatories around the world. It includes recent data for the last
96 hours up to the time the report was compiled. The use of planetary
geomagnetic activity gives a good indication of global activity from
the high latitudes to the low latitudes.
This chart has been constructed from each of the 3-hourly K-index
values reported by all of the participating magnetic observatories.
Each graph line, therefore, represents a 3-hour period of time. The
time on this graph is in Universal Time (relative from Greenwhich,
England). Therefore, the first graph line of this chart represents
the activity occurring from 00 UT to 03 UT (actually, from 00 UT to
02:59:59 UT). The second line represents activity occurring from 03
UT to 06 UT, and so on.
The left-hand side of the chart relates the levels of geomagnetic
activity to the approximate corresponding severity of activity. This
activity is defined from "Very Quiet" levels, which corresponds to
magnetic K-indices of zero, to "Extremely Severe" levels which
corresponds to magnetic K-indices of about nine.
The right-hand side of this chart serves as a _v_e_r_y _r_o_u_g_h _g_u_i_d_e to
the potential severity of magnetic-induction that _m_i_g_h_t be experienced
during corresponding levels of magnetic activity. By "magnetic induc-
tion," we mean the severity of magnetic fluctuations necessary to
begin influencing ground-based systems such as electrical powerline
systems, telecommunications systems, pipeline networks, etc. This end
of the chart is not intended to be a definitive classification, but
rather is only meant to serve as a _p_o_t_e_n_t_i_a_l indicator to possible
magnetic-induction. There are a great many variables that must be
taken into account before magnetic fluctuations can be qualitatively
classified as capable of inducing electrical currents into ground-
based systems. These variables are not considered in this chart.
Only the general level of magnetic fluctuations are considered and are
related to possible magnetic induction. Such localized parameters as
air-earth conductivity, ionospheric current system parameters, electr-
ical field configuration, ground resistivity, and ground-based system
network configurations must be considered (among other things) before
true hazards regarding magnetic induction can be determined. There-
fore, this area of the chart should be used only as a very rough
guide. Nothing more and nothing less. It should be noted, however,
that magnetic fluctuations rated as K-indices greater than 6 generally
become capable of wide-spread electrical current induction. Storms
with fluctuations this high are usually capable of influencing
ground-based systems over wide areas.
The geomagnetic activity graphed in this chart represents the
July 14, 1991
- 9 -
_p_e_a_k global magnetic activity observed during the respective periods.
It does _n_o_t represent average magnetic activity. This is important to
realize. These K-index values are not the same values reported on
radio stations WWV and WWVH. The values reported by these stations
represent the magnetic activity occurring at Boulder, Colorado. Since
this chart is derived from measurements of geomagnetic activity around
the world (not at one specific location), the planetary values are
more valuable and applicable on a global scale.
_2._5. _1_0-_D_a_y _G_e_o_m_a_g_n_e_t_i_c _A_c_t_i_v_i_t_y _F_o_r_e_c_a_s_t
This chart graphs the expected levels of planetary geomagnetic
activity over a 10-day period. Each day is separated into three 8-
hour segments. Each line of the chart therefore represents one eight
hour interval of time. This chart graphs expected conditions relative
to _U_n_i_v_e_r_s_a_l _T_i_m_e. That is, the first line after each date dividing
line represents expected conditions between 00 UT and 08 UT for that
day. The middle graph line represents conditions expected between 08
UT and 16 UT. The last graph line for each day in the chart
represents the magnetic activity that is expected from 16 UT to 24 UT.
This chart should be more easily interpreted than the previous geomag-
netic activity summary chart. It is certainly more valuable.
The predictions are based primarily on data regarding coronal
holes, potential recurrent activity, diurnal trends and potential
solar activity influences. The transient solar component (ex. major
flares) are not included as part of this prediction, since flaring is
extremely unpredictable and forecasts of potential major flaring in
excess of a day or two is very unreliable.
_2._6. _G_r_a_p_h_i_c_a_l _A_n_a_l_y_s_i_s _o_f _S_o_l_a_r _A_c_t_i_v_i_t_y
The graphical chart summarizing solar activity is produced each
week for a 60-day period. This period covers two complete solar rota-
tions and is sufficient to show the cyclic behavior of solar activity
from one cycle to another.
The solar flux (the intensity of solar radio noise observed at
10.7 cm wavelengths) is plotted in this graphical analysis. The
solar flux represents the slowly varying component of the sun (see
part I) and is strongly correlated with the number and intensity of
sunspot groups on the solar surface. The higher the number of sun-
spots visible, the higher the solar flux. As sunspots disappear
behind the western solar limb, the solar flux decreases. The 10.7 cm
solar radio flux is therefore a good indicator of the overall state of
the observed solar environment.
Under normal conditions, the plot lines for the solar flux are
plotted using asterisks (*). However, on days when major flares
erupt, these plot lines are changed from asterisks to "F"'s. This
enables readers to determine the period during the rotational cycle of
the sun when major flares occurred. In most cases, it will be
observed that most of the major flare activity occurs during the rota-
tional peak of each cycle. There are, however, exceptions to this, as
July 14, 1991
- 10 -
will occasionally be noted.
Plot lines are only changed from asterisks to F's when major
flares erupt which meet or exceed an X-ray intensity of class M5.0. A
flare of class M4.9 may be a fairly major event, but is not considered
a major class flare since it never reached M5.0 class intensities.
Most flares, however, are either above or notably below this limit.
There are many more flares of class M3.0 intensity than there are
flares of class M4.0 intensity. Most major flares, therefore, are
observed to occur above this M5.0 transition level. Very few are
borderline cases.
_2._7. _2_0-_D_a_y _S_o_l_a_r _A_c_t_i_v_i_t_y _F_o_r_e_c_a_s_t
The 20-day solar activity forecast chart is constructed based on
the activity which was observed over previous solar rotations, in
addition to the status of the regions which are currently visible on
the sun. The intensity, size and number of sunspots in each region
are all analyzed (among other things) before this prediction chart is
produced.
The plot lines of this chart represent the solar flux levels
which are expected to occur throughout the 20-day period covered by
the chart. The actual flux values will frequently differ from the
actual flux values observed, since predicting the activity of solar
regions is still very difficult to do beyond approximately one week.
Regions behind the sun may be developing which could significantly
alter the shape of the prediction charts. These regions cannot be
seen or detected in any way until they approach the eastern limb of
the sun. Hence, these solar activity predictions should be used only
as a guide. The predictions are generally good at forecasting the
times when the solar flux will peak or reach its minimum during a
rotational cycle, and this can be of tremendous value to people
interested in the level of ionospheric ionization which is propor-
tional to the solar flux.
Flares are not included in this prediction of solar activity.
Flares are extremely difficult to predict, even in the short-term.
Our knowledge of flares has grown rapidly since the early part of this
century. However, our knowledge is still not sufficient to reliably
predict the occurrence of major flares over periods in excess of
several days. Therefore, this graphical solar activity forecast is
limited to a treatment of the solar flux _o_n_l_y. As far as flares go,
an increasing solar flux generally increases the risk for major
flares. The higher the solar flux values, the greater the risk for
major flares, since the solar flux is directly related to the number
and intensity of active regions on the sun.
_2._8. _H_F _R_a_d_i_o _S_i_g_n_a_l _P_r_o_p_a_g_a_t_i_o_n _P_r_e_d_i_c_t_i_o_n_s
This section of the Solar Terrestrial Forecast and Review
involves the propagation of high-frequency (HF) radio waves over
long-distances. It is a forecast of the expected quality of HF radio
signals travelling over long-distances.
July 14, 1991
- 11 -
The quality of radio signals is divided into several areas.
Radio signals which have outstanding strength and stability over
long-distances are categorized as _e_x_c_e_l_l_e_n_t. These conditions are
rarely observed and occur more frequently over the lower latitudes
than the high latitudes. Signals which are abnormally strong and
stable over long-distances are classified as _v_e_r_y _g_o_o_d. These are
above-normal conditions when considering the time of year and the
state of the solar cycle. Signals which are normal for the current
season and state of the solar cycle are given a _g_o_o_d classification.
These signals are generally stable and relatively strong considering
the time of year, but may suffer some minor fading or distortion.
Noise may also be somewhat of a factor, but is generally tolerable.
When signals fall below the normal quality, they may be categorized as
_p_o_o_r. Poor radio signals over long distances are those which experi-
ence moderate to strong fading or flutter, abnormally high levels of
absorption, or increased levels of noise (or any combination of the
above). Long-distance propagation is still usually possible in these
cases, but suffer significantly increased levels of distortion which
may hamper attempts at long-distance voice contacts. _V_e_r_y _p_o_o_r radio
signal propagation occurs when signals experience severe fading and
flutter, high levels of absorption, high levels of noise and high lev-
els of distortion (or any combination of the above). Long-distance
communication usually becomes very difficult during these periods and
may not be possible at all over some regions. When radio signals are
unable to be propagated at all over long distances, or are very poor
over short to moderate distances, communication is rated as being
_e_x_t_r_e_m_e_l_y _p_o_o_r. This category will only usually be encountered at
higher latitudes and during periods of intense geomagnetic storming.
In these forecasts, each day is composed of three 8-hour inter-
vals. These forecasts are also correlated with _l_o_c_a_l _t_i_m_e, not UT
time as are the geomagnetic forecasts. The first plot line of each
day represents the interval between 00 (midnight) and 08 am, local
time. The second plot line represents the period between 08 am and 04
pm (or 08:00 to 16:00) local time and so on.
There is one _v_e_r_y _i_m_p_o_r_t_a_n_t note which should be understood by
all those who use these forecasts as guides. The local time of
attempted communications is a very important factor in long-distance
communications due to the diurnal component. This diurnal component
is _n_o_t considered in these forecasts, nor could it be easily incor-
porated into these charts. The charts are intended to be _g_l_o_b_a_l_l_y
valid. Hence, the obvious diurnal enhancements which occur in differ-
ing ways for different regions cannot be included in this global fore-
cast. The person interested in radio communications is already
expected to have a knowledge of the diurnal enhancements for his or
her region. These charts, therefore, are only intended to aid the
interested communications operator in determining the potential times
when enhanced radio communications may be possible. It is not
intended to reflect the diurnal enhancements which occur, unless the
enhancements are significant.
The forecasts are based heavily on recurrent geomagnetic and
auroral activity, which are primary factors in determining the quality
July 14, 1991
- 12 -
of radio signal propagation conditions. The intensity of ionization
of the appropriate ionospheric layers are also examined when preparing
these charts.
This section is separated into three charts for the high latitude
regions, middle latitudes and the low latitude regions. Global
separation of areas into latitudinal zones is required since the
characteristics and quality of radio propagation differ from zone to
zone.
To make the best use of these charts, the interested reader is
encouraged to follow this procedure. Determine the path endpoint of
your signal. That is, determine the location where you want your
transmitted signal to be received. This is the _p_a_t_h _e_n_d_p_o_i_n_t or _d_e_s_-
_t_i_n_a_t_i_o_n. Your transmitter location is the _s_t_a_r_t_p_o_i_n_t or _s_o_u_r_c_e. Now
draw a great-circle between the startpoint and the endpoint. Next,
determine the most _n_o_r_t_h_e_r_l_y geographical coordinates of the great-
circle connecting the startpoint and the endpoint (we will call this
point the _n_o_r_t_h_p_o_i_n_t) and note the _c_u_r_r_e_n_t _l_o_c_a_l time at the north-
point. After calculating this information, determine what latitudinal
zone the path northpoint lies in. Finally, consult the HF propagation
prediction charts and select the latitudinal zone chart that
corresponds to the _l_a_t_i_t_u_d_e _o_f _t_h_e _p_a_t_h _n_o_r_t_h_p_o_i_n_t. Using the local
time at the path northpoint, select the appropriate day in the chart
and examine the plot line which corresponds to that local time. This
is the propagation quality that can be expected for that path at that
time. Note, however, that you must also consider the local diurnal
signal behavior of your transmission, and the local diurnal signal
behavior at the path endpoint in order to determine the diurnal
characteristics that should be expected. This information is not
given in these charts, but should already be known by the radio opera-
tor who is familiar with the diurnal conditions which occur at his or
her site. In order to be most accurate, this diurnal component must
be considered together with the propagation predictions. Therefore, if
your transmission were conducted during a period of time when you know
both the startpoint and endpoint signals are enhanced, a truer
representation of the propagation quality may be obtained by examining
the prediction charts (using the method above) and increasing the
quality of propagation up by _n_o _m_o_r_e than one level (ie. from "fair"
to "good").
For example, suppose you wanted to communicate between Florida
and Great Britain. Florida is a low latitude zone and Great Britain
is a middle-latitude zone. Next, we draw a great circle between
Florida and Great Britain. If you have no numerical method of doing
this, you can approximate the great circle path by stretching a narrow
piece of paper on a globe of the world such that the ends of the piece
of paper intersect the path startpoint and endpoint (the paper should
be bent so that one of its edges lays flat on the surface of the
globe). The path that this paper makes on the globe will be curved
and represents the great-circle path between Florida and Great Bri-
tain. By examining the great circle path, we are able to see that the
most northerly geographical position on the path is at Great Britain.
Since Great Britain is a middle-latitude region, we consult the middle
July 14, 1991
- 13 -
latitude prediction chart. If you transmitted to Great Britain at 11
am local time on Thursday, the time at the northpoint (which is Great
Britain) would be 3 or 4 pm (depending on the season). Since 3 or 4
pm translates to 15:00 or 16:00 in 24-hour clock format, you would
examine the middle plot line of the chart for Thursday. Note, however,
that the northpoint local time of 15:00 or 16:00 falls close to the
boundary between the middle plot line and the last plot line for
Thursday. Since this is the case, a more accurate representation of
conditions may be obtained by considering a mix of the middle plot
line with the last plot line (possibly averaging the two plot lines).
An important consideration to note when attempting to use these
charts is the time of sunrise and sunset between the startpoint, end-
point and northpoint. Since dramatic changes in ionospheric charac-
teristics occur during these periods, any transmission which crosses
the sunrise or sunset boundaries on its way to the endpoint will
experience correspondinly dramatic changes in behavior and quality.
These charts do not (and could not) account for these variations in
signal quality. The sunrise and sunset ionospheric anomalies are con-
sidered diurnal components in this discussion.
In many cases, the great-circle path of the signal may travel
over more northerly latitudes than the startpoint and endpoint. For
example, a transmission between central Canada and Great Britain may
result in a great-circle path that passes through the high-latitude
regions before reaching Great Britain, even though both the startpoint
and endpoint are middle-latitude stations. In these cases, the most
northerly position of the great-circle path should be used.
If the signal path (or the two path endpoints) are near the boun-
daries of two latitudinal zones, a mix of the propagation predictions
for the two latitudinal zones may be required to yield a more accurate
representation of propagation conditions. For example, if a transmis-
sion were conducted between Denver and Atlantic City, which both
border as low and middle latitude locations, both of the charts for
the low and middle latitude zones should be analyzed and mixed in
order to determine the conditions which might be expected over that
path. Since the distances in this latter example are relatively small
(compared to the latter examples), the northpoint of the signal path
will not significantly affect propagation conditions. This is why we
only examined the latitude of the startpoint and endpoint. For
greater distances, the northpoint must be considered.
_2._9. _V_H_F _P_r_o_p_a_g_a_t_i_o_n _P_r_e_d_i_c_t_i_o_n _C_h_a_r_t_s
The prediction of potential VHF DX is not as simple as it is for
HF. VHF signals have properties which are not usually affected by the
ionospheric layers. In our context, "VHF" will be considered those
frequencies ranging from about 50 MHz to 300 MHz. For information
regarding the major types of VHF propagation which are possible, con-
sult part I of this document.
A great deal of information can be extracted from the VHF predic-
tion charts. Information pertaining to HF communications is also
July 14, 1991
- 14 -
imbedded in these charts. As was done for the HF prediction charts,
the VHF predictions are separated into three charts; one for each of
the major latitude zones.
The upper part of the chart forecasts the quality of potential
_d_i_s_t_a_n_t _V_H_F _s_i_g_n_a_l_s. It does _n_o_t depict the quality of locally
transmitted VHF signals. This is an important point to remember.
Locally transmitted "line of sight" signals can not be affected and
are not affected by geomagnetic activity, auroral activity, or SIDs.
Therefore, only the distant signals which can be affected by these
phenomena are considered in these charts.
As was the case with the other propagation prediction charts, the
VHF prediction charts are separated into groups of three 8-hour daily
intervals. The reference of time used in these charts is _L_O_C_A_L _t_i_m_e,
_n_o_t UT time. That is, the first line of each day in these charts
represents the period between _l_o_c_a_l midnight and 8 am _l_o_c_a_l time.
To use these charts, simply determine what time it is locally and
examine the appropriate day in the charts and the appropriate plot
line within that day. The top portion of the prediction charts define
the quality of VHF signals which can be expected over larger dis-
tances. The bottom chart describes the probability of experiencing
conditions capable of supporting VHF DX. Both charts use the same
reference of time (local time).
The _S_I_D _E_N_H_A_N_C_E_M_E_N_T chart at the upper right-hand corner
describes the probability of a SID (sudden ionospheric disturbance)
temporarily enhancing VHF communications. The probability of SID
enhancements increases with solar activity, but decreases with
increasing latitude. This data is also of value to the HF radio
operator, since SIDs almost always produce short-wave fades (SWFs)
which can disrupt HF communications. Since SIDs are sporadic and very
unpredictable (due to the unpredictable nature of solar flares), they
are predicted as percentages in these charts. SID-related VHF
enhancements _d_o _n_o_t occur on the dark-side of the earth. Neither do
SWFs. Therefore, these SID prediction charts _o_n_l_y apply to those
locations which are still well illuminated by the sun.
The _A_U_R_O_R_A_L _B_A_C_K_S_C_A_T_T_E_R prediction charts are of value to the VHF
radio operator. Auroral backscattering (as was described in part I of
this document) is possible at VHF frequencies during times of
increased geomagnetic and auroral activity. These prediction charts
define the approximate probabilities of VHF propagation via auroral
backscatter over the various latitudes. VHF signals which are pro-
pagated via aurorae can travel fairly large distances. Propagation
via aurorae is therefore considered a potential method of DX on VHF
frequencies. It is, however, a fairly local and sporadic phenomena
and is usually not a widely-encountered form of propagation until
auroral and geomagnetic activity reaches significant storm levels.
To make use of these VHF charts, simply consult the appropriate
plot lines according to what day it is and the local time. The HF
operator may be able to determine what days will prove less reliable
July 14, 1991
- 15 -
as far as day-time propagation goes by examining the probability for
SID related SWFs. Most SWFs, however, are only temporary and do not
pose a significant threat to most HF operators, unless the flares
which produce them are particularly intense.
_2._1_0. _A_u_r_o_r_a_l _A_c_t_i_v_i_t_y _P_r_e_d_i_c_t_i_o_n_s
Auroral activity is predicted for the three major latitude zones
identified earlier. Since the auroral oval itself is situated within
the high-latitude zone, the high latitudes will naturally experience
significantly more auroral activity than the middle and low latitudes.
The prediction charts for auroral activity are most useful to
those people interested in either observing auroral activity, pro-
pagating radio signals using aurorae, or for people interested in
determining the extent of magnetic fluctuations occurring near areas
of auroral activity.
Since auroral activity migrates equatorward during geomagnetic
storms, locations which may usually be outside of the auroral zone
itself may occasionally find themselves _i_n_s_i_d_e the auroral zone during
periods of increased geomagnetic activity. Likewise, as auroral
activity shifts equatorward, low latitudes may be able to begin spot-
ting the activity.
These prediction charts can be used to determine whether or not
potential auroral activity may be intense enough to be seen at low
latitudes, or whether auroral activity will be dull and inactive or
bright and very active.
To use the charts, simply examine the appropriate chart (ex. if
you're a middle latitude location, examine the middle-latitude chart)
and select the column on the day you are most interested. The first
plot line of each day represents the evening twilight period. This is
the period between when the sun sets and before the sky gets com-
pletely dark. The second plot line represents the midnight sector
where the sky remains completely dark (excluding effects of lunar
phase). The last plot line is the morning twilight period and
represents the time when the sky just barely begins to brighten until
the sun rises.
The phase of the moon is not taken into consideration in these
charts. The moon can have a profound effect on the visibility of
auroral activity, but does not affect auroral activity itself. That
is, just because the moon may be blocking out light of auroral
activity does not mean that auroral activity is not in progress.
Indeed, intense auroral storms can occur during a full moon as easily
as they can during new moons. Therefore, these charts represent the
occurrence of auroral activity regardless of lunar phase.
The intensity of auroral activity is measured according to
several parameters. Each of these parameters are discussed in the
Glossary of Solar Terrestrial Terms. In their most basic form, the
parameters (low, moderate, high, etc.) may be considered the
July 14, 1991
- 16 -
brightness of auroral activity during dark-sky conditions (ie. periods
of new moon). However, actual visual movements, color changes and
aerial extent are also considered when classifying auroral activity in
these prediction charts.
_3. _M_o_n_t_h_l_y _S_o_l_a_r _T_e_r_r_e_s_t_r_i_a_l _R_e_v_i_e_w
Every month, statistics and information regarding solar and ter-
restrial activity for the preceding month are gathered and compiled
into a document called the _M_o_n_t_h_l_y _S_o_l_a_r _T_e_r_r_e_s_t_r_i_a_l _R_e_v_i_e_w. This
document contains not only information regarding the nature of
activity of solar and geophysical phenomena during the preceding
month, but also includes a six month solar cycle outlook. This can be
of great value to the radio operator who is interested in determining
what conditions might be like six months down the road. It can also
be of interest to the astronomer who may enjoy searching for auroral
activity or solar flares.
In addition to the written summary, a statistical summary of the
previous month is given in tabular form, summarizing all of the major
solar parameters (ie. solar flux, sunspot numbers, active region
sizes, numbers and types of flares, etc.).
This report is intended to serve as a general summary regarding
activity and phenomena encountered during the previous month. It can
provide some interesting results if data from the report is charted or
graphed or statistically analyzed.
_4. _G_e_o_m_a_g_n_e_t_i_c _S_t_o_r_m _A_l_e_r_t
This alert is posted over the nets whenever magnetic storm condi-
tions reach or exceed minor storm levels over middle latitudes. This
alert may be preceded by a warning if a magnetic storm is expected to
occur but hasn't yet begun.
These alerts always summarize the current level of activity and
may also include descriptions of outstanding geomagnetic activity
occurring prior to the time the alert was issued.
A brief textual forecast of the expected geomagnetic activity is
also included with these reports. This effectively serves as an
intermediate forecast which can be of value during geomagnetic storm
periods when conditions change rapidly.
Full HF and VHF summaries are included with the storm alerts and
all following storm information updates. This information is of value
to those who rely on ionospheric and/or auroral-related communica-
tions.
July 14, 1991
- 17 -
_5. _A_v_a_i_l_a_b_i_l_i_t_y _o_f _A_d_d_i_t_i_o_n_a_l _S_e_r_v_i_c_e_s
Solar Terrestrial Dispatch also supplies other services not men-
tioned in this document, which may be of interest or value to certain
individuals or organizations. One of the additional services provided
are GIC forecast and warning services for individuals or organizations
requiring predictions of possible Geomagnetically Induced Currents
caused by magnetic storming over the high and/or middle latitudes.
Forecasts are produced on a weekly basis, and warnings are issued
whenever conditions (or expected conditions) warrant.
For more information on this or other services not mentioned in
this document, feel free to contact Solar Terrestrial Dispatch by
writing to: Solar Terrestrial Dispatch, Box 357, Stirling, Alberta
Canada, T0K 2E0. Alternatively, for those of you with access to one
of the large electronic networks, you may contact: oler@hg.uleth.ca
for more information (this is an Internet address).
Significant enhanced services will soon be available from Solar
Terrestrial Dispatch for individuals and researchers interested in
obtaining up-to-the-minute solar terrestrial data (ex. x-ray data,
proton data, geomagnetic data, flare-related data, ionospheric data,
etc). For more information or questions regarding the availability of
these or other services, consult Solar Terrestrial Dispatch as given
above.
A recent addition to the services provided by the Solar Terres-
trial Dispatch is the Solar Terrestrial Dispatch computer BBS. This
is a public-access BBS system which regularly obtains fresh forecasts
and data sets. A great deal of additional data is available to
registered users of this BBS, including ionospheric data (total elec-
tron content data, MUF forecasts, short-wave fade forecasts and much
more), geomagnetic data (real-time geomagnetic data less than 2
minutes old, indices and forecasts, etc) and access to other solar
forecasts and data sets (such as real-time x-ray plots, proton plots,
polar cap absorption plots, etc). These are all available to
registered users of the BBS. Registration information may be found by
calling the BBS. The phone number is: (403) 756-3008. Baud rates of
300, 1200 or 2400 baud are accepted. The communications protocol is 8
bit words, 1 stop bit and no parity. Unregistered users are able to
access all of the information which is available over the Internet,
Bitnet and Usenet networks.
_6. _C_o_n_c_l_u_d_i_n_g _R_e_m_a_r_k_s
The solar terrestrial reports which are posted over the networks
contain a great deal of information. Understanding them may take some
time. Applying the information contained in them may take even
longer. This document (part I and II) was developed to help explain
the nature and format of these reports. It was also developed to help
those who are interested in interpreting and applying the information
contained in the reports.
July 14, 1991
- 18 -
It is hoped that this document will help those who are interested
in better understanding the solar terrestrial reports. Questions
and/or comments are welcome. If any further explanations are required
which have not been adequately covered in this document, feel free to
send an inquiry to "oler@hg.uleth.ca" or leave a message to the
"Sysop" on our BBS.
We have learned a great deal over the years regarding the impacts
of solar activity on our terrestrial sphere. But there is still a
great deal more we need to learn before we can expect to master the
art of predicting the impacts of solar activity on the earth. Our
curiosity drives us further and our lust for knowledge quickens our
pace of learning. With developements of new devices and technologies,
we are steadily edging closer to understanding both our terrestrial
environment and the vast environment of space. The educational insti-
tutions and research organizations are the backbones of our knowledge
and growth. We must therefore respect these institutions, support
them, and encourage them so that our body of knowledge is able to con-
tinue expanding into the limitless realm of science.
July 14, 1991
- 19 -
Table of Contents
Introduction .................................................... 1
The Solar Terrestrial Forecast and Review ....................... 2
Summary of Solar Terrestrial Activity ........................... 2
Short Term Solar Terrestrial Forecast ........................... 5
Solar Region Summary ............................................ 6
Geomagnetic Activity Summary .................................... 8
10-Day Geomagnetic Activity Forecast ............................ 9
Graphical Analysis of Solar Activity ............................ 9
20-Day Solar Activity Forecast .................................. 10
HF Radio Signal Propagation Predictions ......................... 10
VHF Propagation Prediction Charts ............................... 13
Auroral Activity Predictions .................................... 15
Monthly Solar Terrestrial Review ................................ 16
Geomagnetic Storm Alert ......................................... 16
Availability of Additional Services ............................. 17
Concluding Remarks .............................................. 17
July 14, 1991