Tag Archives: explainer

How Droughts Work

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The drought of 2012 has gone from bad to worse this summer as relentlessly hot and dry conditions continue to dominate the central United States.

Once drought takes hold of a region, it tends to feed on itself in a vicious cycle. To start, high temperatures increase evaporation rates causing the soil to dry out.  Without plentiful rain to replace the moisture, the sun’s energy heats the ground and the air even further.  The parched ground is then unable to support healthy vegetation that would release moisture into the air through transpiration.  Humidity levels then drop and the air becomes even less able to produce rain, making the affected area even drier.

To break this cycle, a drought stricken region needs more than a few spotty showers. It requires drenching rains on a regular basis.  Alas, these are not in the forecast for America’s desiccated heartland.

Image Credit: Agriculture Emergency Report

Drought Economics

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The widespread drought of 2012 is now considered the worst that the United States has seen in more than fifty years. The nation’s agricultural heartland has been particularly hard hit, and losses there are forecast to have a ripple effect throughout the economy.

According to the U.S. Department of Agriculture, 1,297 counties in 29 states have been designated as natural disaster areas. With grazing lands going barren and staple crops like corn and soybeans wilting in the ground, potential farm yields are plummeting. Following the laws of supply and demand, consumers all across the country will soon be paying higher prices for food.

The cost of many other goods is also expected to rise, as corn is used in a wide variety of products.  It is a key ingredient in items like livestock-feed, ethanol, and anything that contains corn syrup.

Devastating and costly, this drought is likely to intensify as hot and dry conditions continue to dominate the weather in the mid-west.  While not on the same scale as the Dust Bowl of the Great Depression, many analysts expect this year’s drought to rank as a billion dollar natural disaster.

Corn crop withers in drought stricken field.

Image Credit: BuffaloNews

Aphelion

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The Earth will reach its aphelion today at 11 P.M. Eastern Daylight Time.  This is the point in the planet’s elliptical orbit where it is farthest from the Sun.

Today, the Earth is about 152 million kilometers away from its nearest star.  That is approximately 5 million kilometers further than during the perihelion in early January. The exact date of the aphelion differs from year to year, but it’s usually in early July.

The planet’s distance from the Sun does not cause the seasons, but it does influence their length.  As a function of gravity, the closer the planet is to the Sun, the faster it moves. So, at the aphelion, the Earth will move more slowly along its orbital path than at any other time of the year. As a result, summer is elongated by a few days in the northern hemisphere.

The word, aphelion, is Greek for “away from sun”.

Image Credit: astronomy.edu.au

Severe Weather: Watches and Warnings

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Severe weather can happen anytime of the year, given the proper conditions.  This past weekend, for example, unstable air and wind shear combined to send tornadoes roaring through America’s heartland.

Any meteorological event that can cause property damage and loss of life is categorized as severe. It can come in a variety of forms, depending on location and season.  High winds, strong thunderstorms, tornadoes, wildfires, dust storms, hurricanes, floods, and blizzards are all examples of severe weather that occurs in the United States.

When any severe weather event is in the forecast, it is important to understand the difference between the various alerts issued by the National Weather Service.  They include advisories, watches, and warnings.  All should be taken seriously.

  • Advisory:  An “advisory” is issued when significant, but not severe, weather conditions are likely to occur. Residents should exercise caution.
  • Watch:  A “watch” is issued when dangerous weather conditions are possible over the next several hours.  They generally cover a large geographic area.  Residents should be prepared to take action.
  • Warning:  A “warning” is issued when dangerous weather is imminent or already occurring.  They cover a smaller, more specific geographic area.  Residents should take action immediately.

The Enhanced Fujita Scale for Rating Tornadoes

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Tornadoes are nature’s most violent storms.  They damage or destroy everything in their path, including weather equipment.  Therefore, in order to gauge the strength of a tornado, experts use the Enhanced Fujita Scale.  It infers wind speeds from the damage left in the wake of a storm.

Dr. Ted Fujita, a severe weather research scientist at the University of Chicago, developed the original Fujita scale in 1971. The National Weather Service used it from 1973 until 2007, when they adopted the Enhanced Fujita scale. A commission of meteorologists and structural engineers formulated the new model.  It maintains the original scale’s six categories, but refines their wind speeds to reflect differences in construction quality and improved damage survey techniques.

The different categories, EF-0 through EF-5 represent increasing wind speeds and escalating degrees of damage.

Chart Data: NOAA

Perihelion

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Today, the Earth will reach its Perihelion at 8 P.M. Eastern Standard Time.  This is the point in the planet’s orbit where it comes closest to the Sun.

This annual event is due to the elliptical shape of the Earth’s orbit and the off-centered position of the Sun inside that path.  The exact date of the Perihelion differs from year to year, but it’s usually in early January…winter in the northern hemisphere.  We will be furthest from the Sun at the Aphelion in July.

The planet’s distance from the Sun does not cause the seasons, but it does influence their length.  As a function of gravity, the closer the planet is to the Sun, the faster it moves. Today, the Earth is about 146 million kilometers away from the Sun.  That is approximately 5 million kilometers closer than in early July.  This change in distance allows the planet to speed up by about one-kilometer/second.  As a result, winter in the northern hemisphere is about five days shorter than summer.  The opposite is true in the southern hemisphere.

The word, perihelion, is Greek for “near sun”.

The perihelion position of Earth's orbit.

Image Credit: Academy Artworks

Flag Trees

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Objects that indicate the direction of the wind are known as weather vanes.  Not all, however, are man made.

Flag trees, for example, are living weather vanes.  They show the direction of the prevailing wind in a particular location.  On mountain ridges, where trees are constantly exposed to strong winds, the windward facing branches of a tree are often stunted or killed. On the leeward side, the trunk shelters the branches.  This allows them to grow to normal size.  As a result, the tree is sculpted to the shape of the wind and resembles a flag waving in a breeze.

These deformed trees are common features in the windswept sub-alpine landscape, but are not limited to that terrain.  Flag trees can also be seen in the tropics, where the strong, sustained trade winds contort trees in a similar fashion near the equator.

Flag Trees

Photo Credit: jmu.edu

Global Warming v. Climate Change

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We often hear the terms “Global Warming” and “Climate Change” used interchangeably to describe our current environmental conditions.  They are, however, slightly different in scope.

Global warming refers to the rising average temperatures of the atmosphere and oceans across the entire planet.  Scientists report that the Earth’s average surface temperature increased 1.4°F in the last century.  The largest increases have been noted over the past 30 years.

Climate Change refers to the diverse impacts that these increasing temperatures are causing around the globe.  As the additional heat trapped in our atmosphere is circulated around the planet, established weather patterns are being altered.  Different regions, therefore, are being affected in different ways.  Some are getting wetter and others dryer. Many areas are also seeing an increase in the frequency and intensity of extreme weather events.  In addition, coastal regions are being impacted by rising sea levels.

While the Earth’s climate has changed numerous times throughout its long history, the change happening now is occurring very quickly and the vast majority (97%) of experts agree that human activities are the main cause. Regardless of what we call it, Global Climate Change is a subject of great concern that affects us all.