What is the status of sea ice this year?

Posted on October 23, 2023 by WeatherGuys Editor

The surface waters of our polar oceans freeze seasonally, forming a layer of sea ice that varies in thickness from centimeters to meters. The era of polar orbiting satellites has enabled the monitoring of sea ice distribution for more than four decades.

Seasons are reversed between the Northern and Southern hemispheres, so the sea ice maximum and minimum occur at different times of the year. Generally speaking, around mid-September the extent of the sea ice at the south pole is reaching a maximum, while in the Arctic it is approaching a minimum in September as our Northern Hemisphere summer comes to an end.

Arctic sea ice extent for September 19 2023, was 4.23 million square kilometers (1.63 million square miles). The orange line shows the 1981 to 2010 average extent for that day.  (Image Credit: National Snow and Ice Data Center)

This year, the sea ice amount around Antarctica has fallen to a record low. Satellite observations indicate the sea ice extent around Antarctica peaked on Sept. 10. At that time, sea ice covered 6.55 million square miles, which is the lowest winter maximum since satellite records began in 1979. That’s about 386,000 square miles less ice than the previous winter low, set in 1986. The extent of the summer’s Antarctic sea ice also hit a record low in February, breaking the previous mark, set in 2022.

Arctic sea ice reached its minimum extent for this year on Sept. 19, covering 1.63 million square miles. This 2023 minimum extent is the sixth-lowest in the nearly 45-year satellite record. For reference, the combined surface area of the Great Lakes is 94,250 square miles.

The satellite data show a trend in sea ice extent over the Arctic that is decreasing annually at a rate of 4%, plus or minus 1%, per decade. The reduction of Arctic sea ice is rapid, as the northern polar region is warming four times faster than the global average. Over the Southern Hemisphere, satellite data shows no significant trend in sea ice extent. The climate change associated with global warming contributes to melt glaciers in Antarctica, which impacts sea ice extent around the continent.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: History, Seasons

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Is there a typical season for waterspouts?

Posted on October 16, 2023 by WeatherGuys Editor

A waterspout is a whirlwind that forms beneath a cumulus cloud over water. Before you see the waterspout, you may see a funnel-like cloud hanging from the cloud base. The Florida Keys, Gulf of Mexico, and Chesapeake Bay are common regions for waterspouts.

The Great Lakes also have waterspouts, though seasonally. August and September are the most common months for Great Lakes waterspouts to develop, with the full season considered to run from the end of July into October.

Life cycle of fair weather waterspouts (Image credit: NOAA/NWS Sullivan)

There are two types of waterspouts: fair weather waterspouts and tornadic waterspouts associated with severe thunderstorms. The fair weather variety of waterspout is more common than the tornadic and is the most common over the Great Lakes. A fair-weather waterspout is a whirlwind that forms beneath a cumulus cloud and over water and is generally not associated with thunderstorms. A fair weather waterspout develops on the surface of the water and moves upward.

Lake Michigan Waterspout offshore Racine, Wisconsin. Credit: Phil Moeller

Fair weather waterspouts form when cold air moves across warm water. They form when a large temperature difference between the warm water and the overriding cold air exists. Fair weather waterspouts develop in light wind conditions, so they tend to stay in one place or move slowly. They typically have weak circulations and winds, although the bigger spouts can produce wind gusts that can exceed 50 mph and can flip a small boat or damage a dock if they come ashore. Fortunately, these types of waterspouts move relatively slowly and are most often visible from a great distance over the flat expanse of lake waters, so there is ample time to get out of their way.

The International Centre for Waterspout Research is an international organization that monitors and studies waterspouts from all over the globe.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

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Atmospheric and Oceanic Sciences turns 75

Posted on October 9, 2023 by WeatherGuys Editor
The rooftop of the UW–Madison Atmospheric, Oceanic and Space Sciences building. (Photo credit; UW-Madison)

On Friday, the Department of Atmospheric and Oceanic Sciences at the University of Wisconsin-Madison celebrated its 75th anniversary.

When the department was founded in June 1948, the modern science of meteorology was arguably just a few years old, and even basic understanding of the nature of the mid-latitude cyclones that batter us from October to May was truly in its infant stages.

The scholarship within our department over this three-quarters of a century has made enormous contributions to our science and, in turn, to the protection of lives and property through improved forecasts of both tropical and mid-latitude cyclones.

Some of the highlights include the launching of the first weather satellites in the late 1950s and early 1960s. These tools now contribute a huge amount of data to global weather forecasting models, and the UW-Madison remains at the very forefront of the research efforts dedicated to remotely sensing the atmosphere and oceans of Earth.

Developments in the computer models that make such forecasts also has a strong Wisconsin pedigree. The recently retired director of the National Weather Service got all three of his degrees from UW-Madison. The Space Science and Engineering Center, or SSEC, originally developed as an outgrowth of the department, has been at the heart of improved forecasts of tropical weather systems, fire detection and severe storms research for decades.

Clearer understanding of both tropical and extra-tropical weather systems, the global oceans and their interactions with sea ice, the complex climate system and many other important, fundamental issues in the atmospheric and oceanic sciences are being generated every day in our dynamic and diverse department. We are grateful to the citizens of the state of Wisconsin for their support of our endeavors, and those of all of our colleagues at our great University of Wisconsin-Madison.

On, Wisconsin!

Steve Ackerman and Jonathan Martin, professors in the UWMadison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec. wisc.edu or jemarti1@wisc.edu.

Category: History, Meteorology

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Higher overnight lows led to warm September

Posted on October 2, 2023 by WeatherGuys Editor

As we enter the month of October and the traditional end of the warm season, it’s interesting to note that the average temperature last month, through Sept. 28, was 4.0 degrees above normal in Madison.

Monthly climate observations for September 2023 showing deviation from normal. (Image credit: NOAA/NWS Sullivan office)

That is by far the biggest deviation among traditional warm-season months — June, July, August and September. All were warmer than average this year: June was 0.8 degrees, July just 0.5 degree and August only 1.2 degree above the respective norm.

If we break down the September temperature departure into contributions made by increased daytime highs and those made by higher overnight lows, the story gets even more interesting — and more telling. Through Sept. 28, the daily maximum temperatures have averaged 2.7 degrees Fahrenheit above normal, while the overnight lows have been 5.5 degrees warmer than average. Thus, warmer overnight lows last month have contributed about two-thirds of the total temperature anomaly.

Underlying the spike in overnight lows is the fact that the air is systematically a bit more humid as the global temperature increases, and water vapor is a very efficient greenhouse gas. Consequently, if there is more water vapor in the air, it is harder for the surface of the planet to lose energy to space overnight.

Change in overnight lows (°F)
Credit: WICCI

Our lowest daily temperatures have been a bit higher as a result.

This physics is not limited to the warm season — it applies generally.

The bias toward overnight temperature increases as the emblem of climate change is yet another way that the current slow warming of the planet nurtures a level of public skepticism that is out of proportion to the urgency of the threat.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Climate, History, Seasons

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Are day and night of equal hours on the equinox?

Posted on September 25, 2023 by WeatherGuys Editor
The two solstices happen in June (20 or 21) and December (21 or 22). These are the days when the Sun’s path in the sky is the farthest north or south from the Equator. A hemisphere’s winter solstice is the shortest day of the year and its summer solstice the year’s longest. In the Northern Hemisphere the June solstice marks the start of summer: this is when the North Pole is tilted closest to the Sun, and the Sun’s rays are directly overhead at the Tropic of Cancer. The December solstice marks the start of winter: at this point the South Pole is tilted closest to the Sun, and the Sun’s rays are directly overhead at the Tropic of Capricorn. (In the Southern Hemisphere the seasons are reversed.) (Image credit: Britannica)

This year, the autumnal equinox occurred on Saturday, Sept. 23, at 1:50 a.m. Central Time. During the equinox, the sun shines directly on the equator as its position moves from one hemisphere to the other. The word “equinox” is derived from the Latin word “aequus,” which means “equal,” and “nox,” which is the Latin word for “night.” During the 24 hours of the equinox, there are about 12 hours of day and 12 hours of night.

You may hear that daylight and nighttime are of equal length on the equinox. But during the equinox at our midlatitude location, there are approximately eight more minutes of daylight for two reasons: the sun’s shape and atmospheric refraction.

Sunrise time is most frequently defined as when the leading edge of the sun first touches the eastern horizon. Sunset occurs when the sun’s trailing edge touches the western horizon. This provides an extra 2½ to 3 minutes of daylight at our latitude.

In addition, our atmosphere acts like a lens, bending the light from the sun. When the sun is near the horizon, this refraction of the sunbeams has the effect of making the sun appear about a half a degree from its true position. When the sun appears to be on the horizon, it is actually just below the horizon geometrically. Atmospheric refraction advances the time of sunrise and delays the sunset, adding approximately six minutes of daylight. So, we have more daylight than night at the equinox.

The fall equinox marks the midpoint between the summer and winter solstices, and our daylight hours will continue to decrease as we approach the shortest day of the year, with about nine hours of daylight on Dec. 21. Our temperatures will also be getting colder.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.

Category: Meteorology, Seasons

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