Few Degrees

Global average temperatures are expected to increase by about two to thirteen degrees Fahrenheit by the end of the century. That small change in global average temperature can lead to really large changes in the environment. Only a few degrees have made the difference between ice ages, temperate periods, and a hothouse Earth with green poles. During the last ice age, global average temperatures were only seven to thirteen degrees Fahrenheit colder. About 125,000 years ago, average temperatures were only a degree or so warmer than today, but sea levels eventually rose as much as 20 feet higher.

Small changes in the global average temperature also mean heat waves get hotter and droughts get drier. This happens when small changes in the way air and water circulate around the globe take place. For instance, during the wetter and cooler climate of the last ice age, the Great Basin of California was filled by a great lake ringed with pine forests. When the climate became warmer and drier at the ice age's end, the lake dropped 500 feet and lost 90% of its surface area. The pine forests became sagebrush desert. Such changes in precipitation could be just as important as temperature increases for many parts of the Earth.

Some places and some years are going to be warmer or cooler than average. However, summers will get hotter, not only because of higher temperatures but also because humidity will increase. In addition, models predict that in many places, an extreme heat event that we only see once every twenty years today will happen once every three years by the middle of this century. Winters will also be warmer in many places, reducing heating bills. The number of days with frosts is likely to decrease. This means more snow may fall as freezing rain, making ice more of a problem for humans.

http://www.meted.ucar.edu/broadcastmet/climate/print.htm#page_2.0.0

Evidence of Climate Change

Snow and ice reflect the sunrays back to the atmosphere. Without snow and ice, more water can evaporate into the atmosphere where it acts as a greenhouse gas. The ground will then absorb more heat. Snow and ice are melting at rates unseen for thousands of years, and this has profound climate consequences.

Spring snow cover has decreased since 1922 at an average rate of about two percent per decade in the Northern Hemisphere, including a steep five percent drop during the 1980s. River and lake ice don't last as long as they used to either. As permafrost melts in the vast northern tundra, trees locals colorfully call drunken trees are falling over and buildings are crumbling as the ground disintegrates beneath them.

Glaciers have been shrinking across the globe with a few exceptions. In Glacier National Park, for example, there were 150 glaciers in 1850. Today, there are 26. In Switzerland, the Tortin Glacier, which supported a local ski area, shrank so much that the Swiss put a city-block sized insulating sheet over the glacier's edge to slow its retreat. Sea ice is becoming smaller and smaller too especially in the Northern Hemisphere. Satellites have seen average Arctic sea ice shrink by 2.7 percent per decade from 1978 to 2006, with faster melting in summer. In summer 2007, the Northwest Passage north of Canada became navigable for the first time as the polar cap melted to its lowest level on record. 30 years faster than IPCC scientists had predicted. 2008's melt was second only to 2007. 

http://www.meted.ucar.edu/broadcastmet/climate/print.htm#page_2.0.0

Sandstorms

A sandstorm is a very strong windstorm that carries clouds of sand or dust, especially in the desert, and greatly reduces visibility. Sandstorms are also known as dust storms. This wind is usually caused by convections currents, which are created by intense heating of the ground, and is usually strong enough to move entire sand dunes. Air is unstable when heated and the instability in the air will cause the mixture of higher winds in the troposphere with winds in the lower atmosphere, producing strong surface winds. Sandstorms can interfere with travel and sometimes black out entire roads. They can be seen as solid walls of sand that are up to 5,000 high. Sandstorms usually arrive without warning and advance in the form of big wall of dust and debris.

In the United States, sandstorms are very rare due to the lack of large deserts, the development of proper agricultural techniques, and common cloud cover, which will block out some of the sun’s heat. Over grazing and excessive use of water resources can also cause sandstorms. Most sandstorms occur in spring and during the daytime. The last recorded devastating sandstorm in American history was the Dust Bowl which caused a depression.

A way to protect ourselves from sandstorms is to wear goggles and suits. People can also install special air filters in their cars to prevent sand from getting into the engine. Sandstorms do not only have the potential to damage possessive items we own but does also has the potential to harm humans. Sand particles will clog air passages and cause the person who breathes them in to choke. Dust particles may cause an allergic reaction. Sand and dust have also been known to be capable of carrying infectious diseases.



http://library.thinkquest.org/03oct/01027/sandstorm.html

Rainbows

A rainbow is a circular arc of concentric colored bands, caused by a combination of refraction and reflection of sunlight by raindrops. (Refraction is the bending of light as it passes from one transparent medium into another transparent medium.) Sunlight striking a shaft of falling raindrops is refracted twice and internally reflected by each drop of rain. A solar ray is refracted as it enters a raindrop. Then, the ray is reflected by the inside back of the drop before being refracted again as it exits the drop. Each person sees his or her own rainbow.

Because of reflection, a rainbow appears to an observer who has his or her back to the Sun and is facing a distant rain shower. A rainbow never forms when the sky is completely cloud covered. The Sun must be shining. For the reason of geometric considerations, the Sun can be no higher than 42 degrees above the local horizon in order for someone on the ground to see a rainbow. If the solar altitude is greater than 42 degrees, then the returning solar rays are not directed towards Earth’s surface. A rainbow is more likely during a morning or evening shower than a shower at noon. At middle latitudes, weather systems usually progress from west to east so that appearance of a rainbow to the east in the early evening usually signals improving weather. Rain showers are moving away toward the east and clearing skies are approaching from the west, where the Sun is setting. A morning rainbow to the west signals approaching rain.

When raindrop refraction disperses sunlight into its component colors, it forms the concentric bands of color of a primary rainbow. From outer to innermost band, the colors are red, orange, yellow, green, blue, and violet. In some occasions, a secondary rainbow appears about 8 degrees above the primary rainbow. Double reflection within raindrops produces the secondary rainbow with the order of colors reversed.

http://www.photocentric.net/rainbow_physics.htm



Features of a Hurricane

A hurricane is more than a point on weather map, and its path is more than a line. A hurricane has several futures. The main features of a hurricane are the rainbands on its outer edges, the eye, and the eye wall. Air spirals in toward the center in a counter clockwise direction and out the top in a clockwise pattern. In the center of the storm, airs sinks and forms a cloud free eye.

The hurricane’s center is known as the eye. It is relatively calm and has a clear area usually 20-40 miles across but sometimes as small as 5 miles or as large as 60 miles. When in the midst of a hurricane strong winds and rain can suddenly stop and the sky clears when the eye comes over a region. Then as soon as the eye moves out of that region rain and wind begins again but from the opposite direction.

The dense wall of thunderstorms surrounding the eye is the eyewall. The circle of thunderstorms around the calm eye has the strongest winds within the storm. Changes in the structure of the eye and eyewall can cause changes in the wind speed which is an indicator of the storm’s intensity. The eye can grow or shrink in size and could double or concentric eyewalls can also form. Concentric walls usually occur in major hurricanes. Concentric walls tend to weaken the storm but they strengthen again when a single eyewall is in place.

A hurricane’s outer rainbands can extend a few hundred miles from the center. These dense bands of thunderstorms range in width from a few miles to tens of miles. Typical hurricanes are about three hundred miles wide. A hurricane rainband is the location where a tornado usually occurs at.

http://www.meted.ucar.edu/hurrican/chp/print_2.htm



What Is a Hurricane?

A hurricane is an intense, rotating oceanic weather system that possesses maximum sustained winds exceeding 74 mph. In North America, we call this storm a hurricane. In other parts of the world, a hurricane is known by other names. In the Western North Pacific they are known as a typhoon and in the Indian Ocean and the Western South Pacific as a tropical cyclone. It forms over tropical oceanic regions. Hurricanes are generally smaller storms in mid-latitudes, typically about 500 km in diameter. In the Northern Hemisphere, the air spins inward and in a counterclockwise direction. Hurricanes depend on six conditions to form.

1.       A pre-existing disturbance providing some initial spin and flow into the system.

2.       Warm ocean temperatures (at least 80 degrees Fahrenheit) to a depth of about 150 ft.

3.       Relatively light winds that do not change much in direction and speed up through the atmosphere.

4.       A location at least 300 miles from the equator. Tropical cyclones require some of the spin provided by the Coriolis Effect.

5.       An atmosphere that cools enough with height to allow thunderstorms to develop.

6.       An atmosphere that is moist enough to fuel the thunderstorm.

Tropical cyclones are classified into four types, based on their wind speeds. These are the terms commonly used by forecasters:

·         Tropical Depression: Maximum sustained winds of 38 mph or 33 knots

·         Tropical Storm: Maximum sustained winds of 39-73 mph (34-63 kt)

·         Hurricane: Maximum sustained winds of 74 mph (64 kt) higher

·         Major Hurricane: Maximum sustained winds of 111 mph (96 kt) or higher

Hurricanes are categorized according to the strength of their winds using the Saffir-Simpson Hurricane Wind Scale.  A Category 1 storm has the lowest winds speeds, while a Category 5 hurricane has the strongest.

·         Category 1: Winds of 74-95 mph; Very dangerous winds will produce some damage

·         Category 2: Winds of 96-110 mph; Extremely dangerous winds will cause extensive damage

·         Category 3: Winds of 111-130 mph; Devastating damage will occur

·         Category 4: Winds of 131-155 mph; Catastrophic damage will occur

·         Category 5: Winds of 155+ mph; Catastrophic damage will occur

http://www.comet.ucar.edu/nsflab/web/hurricane/312.htm

Hurricane Rita

On September 18, 2005, less than a month later after Katrina had devastated the central Gulf Region, Hurricane Rita formed from a tropical depression that had formed the same day near the Turks and Caicos Islands. The storm increased intensity over the next two days, becoming category 1 on the 20^th. Later that afternoon, Rita grew to a category 2 as it passed near the Florida Keys and South Florida. It caused sustained tropical storm force winds on Key West with gusts of up to 76 mph.

Rapidly intensifying, Hurricane Rita tracked westward into the Gulf of Mexico. By the afternoon of the 21^st, Rita reached category 5 strength on the Saffir-Simpson scale, with winds of 165 mph. It became the second hurricane of the season to reach category 5 and first time in record that two hurricanes reached category 5 strength in the Gulf of Mexico in the same season.

Rita continued to intensify and reached wind speeds of 175 mph and the minimum central pressure of the storm reached to 897 mb. It became the third lowest on record for the Atlantic Basin, after Hurricane Gilbert (888 mb) and 1935 Labor Day Hurricane (892 mb).

During the afternoon of the 22^nd, Rita started to weaken due to an eye wall replacement cycle and perhaps some influence of slightly cooler sea surface temperatures. Hurricane Rita’s intensity dropped to a surface wind speed of 145 mph and continued to gradually weaken over the next 36 hours prior to landfall. Rita tracked west northwest on the 23^rd and made landfall at the Texas Louisiana border early on the 24^th at a category 3. Hurricane force winds were sustained more than 150 miles inland.

http://www.ncdc.noaa.gov/special-reports/rita.html