ATMOSPHERIC PHENOMENA

Energy Transport

One of the important links in the global atmospheric circulation is the transport of energy from the tropics to higher latitudes. Deep convective storms within the intertropical convergence zone are the primary agents for converting latent energy into internal energy, providing the driving force for poleward energy transport. Ocean currents such as the Gulf Stream, are also responsible for moving excess heat gained in the tropics to the poles, thus maintaining the Earth's thermal equilibrium. On average, the atmosphere and the ocean are equal partners in the amount of heat they transfer poleward. Sea-surface temperatures are used to determine how much heat is transferred between the atmosphere and the ocean.

air12.gif



Tropical and Subtropical Precipitation

Precipitation is the transfer of liquid or solid water from the atmosphere to the surface, after condensation. This strongly affects the climate of the Earth by providing a sink of heat energy in some locations, through melting and evaporation, and a source of heat energy in others, through condensation. Evaporation, transportation, and precipitation of water strongly contributes to the redistribution of energy from the equator to the poles.

One of the important constituents of the Earth's atmosphere is water, which changes among the solid, liquid, and gaseous phases at the temperatures and pressures found at the surface and in the troposphere.

In the series of images above, the amount of tropical rainfall is measured in millimeters per day. White colors represent the lowest amounts of precipitation and reds represent the highest.

air13a.gif

air13b.gif

air13c.gif

air13d.gif

air13e.gif

air13f.gif

air13g.gif

air13h.gif

air13i.gif

air13j.gif

air13k.gif



Thunderstorms

A thunderstorm is a local storm resulting from warm humid air rising in an unstable environment. Air may start moving upward because of unequal surface heating, the lifting of warm air along a frontal zone, or diverging upper-level winds (these diverging winds draw air up beneath them). The scattered thunderstorms that develop in the summer are called air-mass thunderstorms because they form in warm, maritime tropical air masses away from other weather fronts. More violent severe thunderstorms form in areas with a strong vertical wind shear that forces the updraft into the mature stage, the most intense stage of the thunderstorm. Severe thunderstorms can produce large hail, forceful winds, flash floods, and tornadoes.


Energy transport is the amount of thermal and latent heat that is moved by the atmosphere and oceans from one latitude to another in a constant effort to achieve thermal equilibrium over the Earth. Thunderstorms are one of the main mechanisms of the transfer.

In the movie at the left, GOES-9 has captured a view of a thunderstorm building over Florida's Palm Beach starting at about 4:30 P.M. on July 2, 1995. Central Florida is the lightning capital of the world, with over 90 thunderstorm days per year. You can begin the video by clicking on the single arrow button on the movie bar or you can advance one frame at a time by clicking on the forward or reverse buttons on the right of the movie bar.

GOES-9 Movie



Global Observations of Lightning

Lightning is one of the more spectacular responses of the atmosphere to thermodynamic and dynamic forcing and, consequently, contains useful information about the atmosphere. The processes that lead to the production of lightning are tightly controlled by updraft intensity and the formation of precipitation. Thus, lightning activity is closely coupled to storm dynamics and microphysics, and therefore, should exhibit some quantifiable relationships to the global rates, amounts, and distribution of convective precipitation and to the release and transport of latent heat from thunderstorms.


The movie at the right utilizes GOES-8 infrared imagery and shows lightning events along a squall line on April 30, 1996. Yellow dots represent one lightning event, red dots represent two events, and magenta dots represent three. You can begin the video by clicking on the single arrow button on the movie bar or you can advance one frame at a time by clicking on the forward or reverse buttons on the right of the movie bar.

Lightning seems to initiate soon after the onset of strong convection, when significant cloud mass and ice have formed in the upper regions of a thunderstorm. Lightning activity also tends to track the updraft in both amplitude and phase, with rates increasing as the updraft intensifies and decreasing rapidly with cessation of vertical growth.

The air surrounding a lightning bolt is heated to 50,000·F. It is this rapid heating and cooling of the air that triggers a pressure (sound) wave in the atmosphere that we hear as thunder. Lightning causes several hundred million dollars in damage to property and forests each year. There are an average of 93 deaths and 300 injuries due to lightning in the United States each year.

Lightning Movie


Hurricanes

A hurricane is one of nature's most awesome phenomena. Called typhoons when they originate in the western Pacific, they are low-pressure weather systems characterized by strong winds blowing in a circular pattern about a central core. In addition, they have the potential to spawn dangerous tornadoes. The strong winds and excessive rainfall also can produce abnormal rises in sea levels and flooding.


The central core, also known as the "eye" of the hurricane, is remarkably calm, particularly in contrast to the surrounding winds. As a hurricane passes over a certain location, people in the area witness violent winds and rains, followed by a period of calm as the eye passes over them. Once the eye has passed over, the raging winds and heavy rains again thrash the land.

Research leading to an increased understanding of these awesome storms will be performed using
data from the Moderate-Resolution Imaging Spectroradiometer (MODIS) and other instruments scheduled for flight on the EOS satellites.

The movie on the right shows a rapid scan of Hurricane Luis on September 6, 1995. Each "frame" was taken from the GOES-9 weather satellite at intervals starting at 7:40 P.M. and ending at 10:58 P.M. You can begin the video by clicking on the single arrow button on the movie bar or you can advance one frame at a time by clicking on the forward or reverse buttons on the right of the movie bar.

Hurricane Luis Movie



Hurricane Categories

Hurricanes are categorized by their sustained winds (depicted in the scale at the right). They are assigned names, which occur alphabetically, by the national and international weather services several years in advance. Hurricane processes are undergoing continuing research.

air14.gif



1995 Record Hurricane Season

The 1995 hurricane season was a record breaking year, second only to 1933, when 21 storms occurred. Out of the 19 tropical storms that occurred in the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea that year, 11 achieved hurricane status (winds over 74 mph). 1995 presented the greatest number of days on record with tropical storm systems, 110 out of the 183 day Atlantic season, or roughly 60%. Three of those major storms were Hurricanes Allison, Erin and Opal.


HURRICANE ALLISON

The 1995 season sprung to life on June 3 in the Gulf of Mexico with the birth of tropical depression 1 which evolved into Hurricane Allison on June 4. Heavy rains associated with Allison caused the collapse of 32 structures in western Cuba. One person was killed and three injured due to these collapses.

Allison made U.S. landfall near Alligator Point, Florida (Panhandle) on June 5 at 10:00am EDT as a tropical storm with maximum sustained winds of approximately 69 mph. The storm weakened further as it headed inland to Georgia, but tropical storm force winds persisted over Apalachee Bay until 5:00pm EDT on the 5th. Allison diminished to a tropical depression over southern Georgia by 8:00pm on June 5th.

In the U.S., there were no direct deaths due to Allison. Damage was greatest in the Florida coastal sections of Dixie, Levy, Taylor and Wakulla counties, mainly from storm surge effects, with 60 houses and businesses damaged. A house collapsed at Bald Point in Franklin County (Florida). About 5000 people evacuated from the coast. Other coastal effects included mostly minor beach erosion, damage to sea walls and coastal roadways, and the sinking of several small boats. Otherwise, minor wind damage to roofs, signs, power lines and trees occurred over most of the north Florida peninsula.

Total damage in Florida was estimated at $860,000, and the tornado near St. Mary's, Georgia, caused about $800,000 in damage, bringing Allison's overall U.S. damage figure to $1.7 million.

HURRICANE ERIN

1995 also tied the 1966 record for the number of storms during the month of July, producing four storms: Tropical Storm Barry, Tropical Storm Chantal, Tropical Storm Dean, and Hurricane Erin.

Erin made landfall around 2:00am EDT on July 2nd near Vero Beach, Florida as a Category 1 hurricane on the Saffir/Simpson Hurricane Scale, with estimated maximum wind speeds of 86 mph.

Erin's track bent to west-northwest while the cyclone crossed the Florida peninsula during the morning and early afternoon of the 2nd. The cyclone weakened to a tropical storm with 58 mph winds during that period, but remained well-organized. Upon emerging into the eastern Gulf of Mexico, Erin reintensified on a track that gradually swung back to the northwest. Final landfall occurred near Pensacola, Florida during the late morning of the 3rd. Erin had around 98 mph winds (Category 2) in a small area of its northeastern eyewall when that part of the hurricane came ashore near Fort Walton Beach in the western Florida panhandle.

Erin weakened to a tropical storm in southeastern Mississippi overnight on the 3rd/4th and eventually to a tropical depression on the 5th. The depression then merged with a frontal system over West Virginia on the 6th.

Erin caused an estimated $700 million in damage and six related deaths. These casualties occurred in the Atlantic and Gulf of Mexico waters off Florida and all were drownings.

The American Insurance Services Group estimated $375 million as the loss to insured property in the United States caused by Erin ($350 million in Florida, $20 million in Alabama, and $5 million in Mississippi). Because the total loss is usually estimated by the National Hurricane Center to be up to about double the insured loss, the total U.S. loss is tentatively estimated at $700 million.

The most significant structural damage from the final landfall occurred on Pensacola Beach, Navarre Beach, around Mary Esther and in northeast Pensacola. More than 2,000 homes were damaged there and crop losses were reported. Some beach erosion was reported west of Navarre Beach. Farther inland, widespread tree, power line and crop damage was reported and about 100 homes were damaged in Alabama.

HURRICANE OPAL

While the 3 named storms born in September did not tie any records, September did see the strongest and most destructive storms of the 1995 season, one of which was Hurricane Opal.

Opal intensified into a category 4 hurricane on the Saffir/Simpson Scale early on October 4th. The minimum central pressure of 916 mb, with maximum sustained surface winds estimated at 150 mph, occurred when the hurricane was centered about 250 nautical miles south-southwest of Pensacola, Florida at 6:00am on October 4th. After slightly weakening to a marginal Category 3 hurricane, Opal made landfall at Pensacola Beach, at 6:00pm on October 4th.

The minimum central pressure at landfall was 942 mb. Maximum sustained surface winds were estimated at 115 mph in a narrow swath at the coast near the extreme eastern tip of Choctawhatchee Bay about midway between Destin and Panama City, Florida. Although no official reports of surface winds were received within this area, data from reconnaissance aircraft and Doppler radar suggest that the peak winds occurred in this location. It should be emphasized that the strongest winds were in a very limited area and most of the coastal areas of the Florida panhandle experienced winds of a Category 1 or Category 2 hurricane (between 75 and 109 mph). Although the winds were diminishing at the time of landfall, extensive damage due to storm surge and breaking waves occurred over most of the coastal areas of the Florida panhandle.

Opal weakened rapidly after moving inland, becoming a tropical storm over southern Alabama and a tropical depression over southeastern Tennessee. The cyclone was declared extratropical as it moved northeastward over the Ohio Valley and eastern Great Lakes into southwestern Quebec. The strongest winds occurred well away from the center of the cyclone during the extratropical stage.

Opal proved to be the season's strongest and costliest hurricane for the United States. The total number of deaths directly associated with Opal was 59; 31 in Guatemala from flooding during the developing stages of Opal, 19 in Mexico from flooding, 1 in Florida from a tornado, 2 in Alabama from a tree falling on a mobile home, 5 in Georgia from falling trees, and 1 in North Carolina from a tree falling on a mobile home. There were no reported deaths due to storm surge flooding, which is remarkable in view of the vulnerable population and extensive salt water damage observed.

If the estimate of insured property damage proves to be correct, the total damage estimate from Hurricane Opal could reach $3 billion. Without adjustments for inflation, Opal could rank as high as third on the list of costliest twentieth-century U.S. hurricanes. With adjustments for inflation, Opal will likely still be ranked in the top ten on that list.



Volcanoes

The Earth's surface is a series of huge plates. Tectonic plates are driven by geothermal heating from deep within the Earth which generates magma that comes to the surface. As the plates move, they collide, one plate riding on the top of the other. Mountains are formed, the Earth trembles and quakes, and dust and gases are ejected into the atmosphere.


While topographical changes created by volcanic action are a crucial element of the Earth's surface, volcanoes also have a profound effect on our atmosphere and directly impact the global climate.

Mt. Saint Helens erupted in Washington state on May 18, 1980. The eruption sent a blast of rocks, ash, and gases which traveled across the landscape at speeds up to 670 miles an hour with temperatures reaching up to 600 degrees Fahrenheit inside the blast. This force stripped trees from hillsides as far away as 6 miles from the volcano, as can be seen in the above image.

At right, the photograph catches a moment of Mt. Pinatubo's massive eruption on June 12, 1991 (Philippine Institute of Volcanology and Technology).



Volcanoes and Global Climate Change

This figure shows that as volcanoes erupt, they blast huge clouds into the atmosphere. These clouds are made up of particles and gases, including sulfur dioxide. Millions of tons of sulfur dioxide gas from a major volcanic eruption can reach the stratosphere. There, the sulfur dioxide converts to tiny persistent sulfate particles, referred to as aerosols. These sulfate particles reflect energy coming from the sun, thereby preventing the sun's rays from heating the Earth. Volcanic eruptions are thought to be responsible for the global cooling that has been observed for a few years after a major eruption. The amount and global extent of the cooling depend on the force of the eruption and, possibly, on its latitude.

air15.gif



Volcanoes and Global Temperature Changes

When Mount Pinatubo erupted in the Philippines in June 1991, it spewed about 20 million tons of sulfur dioxide into the atmosphere reaching heights of 25 km. Dispersed by stratospheric winds, the sulfur dioxide was transformed to sulfuric acid, forming a layer of small aerosol particles that traveled around the entire globe by mid-July. These particles increased the amount of sunlight reflected back to space, thus having a cooling effect on the Earth's climate. The cooling caused by the Mount Pinatubo eruption helped to make 1992 the coolest year since 1986.

In the chart at the left, the red line represents modeled temperature changes (in degree Celsius) and the blue line represents temperature changes observed from meteorological ground stations.

air16.gif



Ozone Depletion and Volcanoes

Another possible effect of a volcanic eruption is the destruction of stratospheric ozone. Researchers are now suggesting that particles containing sulfuric acid from volcanic emissions may contribute to ozone loss.
When chlorine compounds resulting from the breakup of chlorofluorocarbons (CFCs) in the stratosphere are present, the sulfate particles change the stratospheric nitrogen balance, which leads to increased reactive chlorine, which then reduces ozone.

air17.gif



Mt. Pinatubo Sulfur Dioxide

By September 21, 1991, a few months after Pinatubo's eruption, the increased levels of sulfur dioxide were measured worldwide by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite and are depicted in this figure.

The color scale in this image relates to sulfur dioxide amounts in parts per billion ranging from less than 1.0 (violet) through blue, green, yellow, and orange, to greater than 10.0 (red).

Another Microwave Limb Sounder (MLS) instrument is scheduled to be launched on the EOS-Chemistry satellite series beginning in 2002. One of its applications will be the investigation of worldwide levels of sulfur dioxide.

air18.gif



Mt. Pinatubo Sulfur Dioxide Cloud (TOMS)

Two days after Pinatubo's eruption, the resultant cloud of sulfate particles had separated from the volcano and drifted 1200 kilometers to the Gulf of Siam. The leading edge of the cloud then sheared away from the main cloud and drifted over the southern tip of India, traveling 5500 kilometers in 36 hours.

The "Milli Atm cm" scale shown on these three images indicates the derived vertical column thickness of sulfur dioxide in units of 0.001 cm at standard temperature (0·C) and pressure (the average pressure at the surface of the Earth.) Reds indicate higher thickness and blues indicate lowest.

air19a.gif

air19b.gif

air19c.gif