How does carbon dioxide affect global warming?

Posted on May 14, 2014 by WeatherGuys Editor

Since 1958, a continuous measurement of the carbon dioxide content of the atmosphere has been made at Mauna Loa Observatory in Hawaii. These observations were initiated by Charles Keeling, who died in 2005, and have been maintained by his son Ralph ever since.

Sunshine is a manifestation of solar radiation and when it is absorbed by the surface of the Earth, the surface heats up and emits a different kind of radiation, known as infrared radiation. Carbon dioxide is a special chemical in that it is transparent to solar radiation and yet it absorbs infrared radiation. Thus, the presence of carbon dioxode in our atmosphere allows sunshine to penetrate to the surface but inhibits the emission of infrared radiation to space.

The consequence of the absorption of infrared radiation by carbon dioxide in the atmosphere is that Earth is much warmer than it has any right to expect based upon its distance from the Sun. In fact, Earth’s average surface temperature is 59 degrees Fahrenheit when it would be 0 if carbon dioxide and other such greenhouse gases (like water vapor and methane) did not exist in our atmosphere.

When Keeling began his measurements in 1958, the atmosphere contained 315 carbon dioxide molecules for every million molecules of gaseous atmosphere. April 2014 was the first month in 56 years in which the monthly average carbon dioxide fraction topped 400 molecules per million (it was 401.33).

The continual increase in this carbon dioxide fraction is considered to be the main contributor to the global temperature increase known as global warming. Such values are a first in human history and likely represent the highest carbon dioxide fraction in our atmosphere in at least the last 800,000 years. It is high time that we had a sober, data-driven discussion about the hazards presented by this dangerous trend. Analytical, skeptical science has to be central to this discussion.

Category: Climate, Meteorology

Comments Off on How does carbon dioxide affect global warming?

Ask the Weather Guys: Like it or not, numerical technique vastly improved forecasting

Posted on May 6, 2014 by WeatherGuys Editor

Pretty good forecast last week, wasn’t it?

Though last week’s persistent cloudiness and intermittent rain was almost surely met with derision by all, it is hard to imagine that many people were surprised by it, as the forecasts very accurately painted the gloomy picture several days in advance.

This advance warning was provided by the National Weather Service through the triumph of numerical weather prediction (NWP). Tuesday May 6th is the 59th anniversary of the issuance of the first NWP forecast in world history.

That forecast was issued in 1955 by the Joint Numerical Weather Prediction Unit headed by Jule Charney, a theoretical meteorologist from MIT, and John von Neumann, a computer scientist from Princeton. It was a dismal failure. In fact, a number of noted atmospheric scientists who had, to that point, offered only polite support for the development of NWP, were quick to use this initial failure as proof of the intractable nature of the challenge of numerically forecasting the weather.

The skeptics were on the wrong side of an amazing history. By 1965, the accuracy of a one-day forecast was substantially improved.

Today, we enjoy the fruits of the persistence of the pioneers who never wavered in their confidence that NWP was a worthy endeavor.

Last week’s persistent clouds and rain, forecast several days in advance, are just the latest example of the remarkable success of NWP. It may not be an exaggeration to claim that NWP is among the most underrated scientific advancements of the second half of the 20th century.

Category: Meteorology

Comments Off on Ask the Weather Guys: Like it or not, numerical technique vastly improved forecasting

Are the jet stream and tornadoes related?

Posted on April 28, 2014 by WeatherGuys Editor

Wintertime weather is driven largely by the parade of upper-level weather systems carried rapidly eastward by the high level winds known as the jet stream.

The jet stream is a ribbon of high-speed wind (located at nearly 6 miles above the surface) that is related to the strength, and location, of the pole-to-equator temperature contrast.

As we all know too well after this past winter, cold polar air can spill as far south as Mexico during our winter. This drags the jet stream as far south as southern Texas during the depth of winter.

As we enter the middle of spring, the southern latitudes of our country begin to warm up rapidly and our attention turns to the return of severe weather season.

Though severe weather includes more than just tornadoes, these storms are the season’s highest-profile events. But the climatology of tornadoes varies depending on geography.

We are already past the tornado frequency maximum over the Gulf Coast states (Louisiana, Alabama and Mississippi) that occurs in mid- to late March. From April to May, the tornado frequency maximum occurs over the Southern Plains states of Oklahoma, Texas and Kansas. By June through August, it moves to the Great Lakes states and High Plains.

This northward migration of tornadoes reflects the northward migration of the jet stream. Since the jet stream is tied to the southern edge of the cold air centered on the Pole, as the seasons change from late winter to late summer, the polar cold air retreats to the north dragging the jet stream, and the tornado season, with it.

Category: Seasons, Severe Weather

Comments Off on Are the jet stream and tornadoes related?

How long were Madison lakes frozen this year?

Posted on April 21, 2014 by WeatherGuys Editor

Lakes Mendota, Monona and Wingra opened during the second week of April.

Lake Mendota officially froze Dec. 16 and opened April 12, for an ice season  of 117 days, which is 12 days longer than the median duration.

Despite the persistent and sometimes brutal cold we experienced this winter  in southern Wisconsin, the 117-day ice season pales in comparison to the record  for Mendota, set in 1880-81, of 161 days. That’s nearly a month and a half  longer than this year’s ice season.

Lake Monona froze Dec. 10 and opened April 10 for a season of 121 days,  exceeding the median duration by 17 days.

Lake Wingra froze Nov. 27 and opened April 9 for a season of 133 days, also  17 days longer than the median.

Interestingly, the largest lake, Mendota, took only three more days to open  than did the smallest lake, Wingra.

Because there is so much more water in Lake Mendota compared to Lake Wingra,  the big lake froze 19 days later than the small lake. This testifies to the  substantially larger amount of heat energy that must be removed from the larger  Lake Mendota before it can finally freeze.

This energy is deposited in the overlying atmosphere where it can be used to  make the lakeshore temperatures warmer than those at locations far from the  lake. Such heat lost from the lake in late autumn, since it was originally  deposited in the lake by sunlight during summer and fall, represents a delay in  the transfer of energy from the summer-autumn sun to the wintertime air.

Category: Climate, Seasons

Comments Off on How long were Madison lakes frozen this year?

Why does the moon look red during a lunar eclipse?

Posted on April 14, 2014 by WeatherGuys Editor

Why does the moon look red during a lunar eclipse?

In a total lunar eclipse the sun, earth and moon line up and the Earth casts its shadow on the moon.

The moon is always a full moon during a total lunar eclipse and it never goes completely dark. It appears reddish for the same reason that sunsets and sunrises often have a red tint.

The Earth’s shadow has two parts: the umbra and the penumbra. A small amount of the sun’s energy directly shines within the penumbra.

None of the sun’s rays shine directly in the umbra part of the shadow, so it is the darkest part of the shadow. A total lunar eclipse occurs when the moon travels through Earth’s umbra.

The umbra is not pitch black because of the Earth’s atmosphere. Sunlight is scattered, or redirected, in all directions by the Earth’s atmosphere into the penumbra and umbra.

As light passes through the atmosphere, the blue colors are scattered out of the path. Red and orange light passes through the atmosphere and is scattered into the shadow zone. If our planet had no atmosphere, then the moon would be completely dark during a total lunar eclipse.

A total lunar eclipse will occur Monday-Tuesday across the United States and Canada. If it is cloudy or you miss seeing this total lunar eclipse, three more total lunar eclipses will be viewable from our area on Oct. 8 of this year, and next year on April 4 and Sept. 29.

The last total lunar eclipse viewable from our area was in December 2011, so this many over the next year is a bit unusual.

 

Category: Uncategorized

Comments Off on Why does the moon look red during a lunar eclipse?