How is air pollution measured?

Posted on April 10, 2023 by WeatherGuys Editor

There are different sources of air pollution, including human-generated emissions from the burning of fossil fuel, as well as natural sources such as wildfires, volcanic eruptions and dust storms.

Particle pollution is referred to particulate matter (PM) and is made up of small, suspended solid or liquid particles. The amount and density of pollutants in the air are converted into an Air Quality Index (AQI). An AQI of less than 50 is considered safe, while unhealthy conditions have an AQI above 100. The chemical composition of the pollutant can also be a health concern.

Some air quality monitors use lasers to determine the density of particulate matter. Other methods include passing air through filters and then measuring the material collected on the filter.

The Environment Protection Agency has a nationwide network of monitoring sites to measure conditions of particulate matter. PM2.5 describes fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller. Analysis of observations demonstrate that the average PM2.5 concentration has been decreasing nationally, an indication that air quality is improving.

Last week NASA launched a new satellite instrument to monitor air pollution. The Tropospheric Emissions: Monitoring of Pollution, or TEMPO, was launched into geostationary orbit on Thursday. TEMPO is the first space-based instrument to monitor major air pollutants hourly and at high spatial resolution of 4 square miles.

Observations of such temporal and spatial detail enable research studies of rush hour pollution, the movement of pollution from forest fires, and even the impact of fertilizer application. The TEMPO measurements will join a global satellite constellation of observations that will track pollution around the globe.

This animation demonstrates the east to west scanning strategy of TEMPO’s hourly profile of air pollutants over North America using proxy NO2 data. (Credit: Robert Carp, SSEC)

Scientists at UW-Madison’s Space Science and Engineering Center are members of NASA’s TEMPO science team and will monitor the presence of air pollutants over North America and help improve air quality forecasts.

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, Weather Dangers

Comments Off on How is air pollution measured?

Is March weather susceptible to being unusual?

Posted on April 3, 2023 by WeatherGuys Editor

The adage about March weather coming “in like a lion, out like a lamb” was far off the mark for southern Wisconsin this year.

In Madison, it was not a particularly cold month as the average temperature was only 0.8 degrees below normal. However, we had the second-snowiest March ever — and snowiest since the record was set in 1959 — with 25.3 inches of accumulated snow. In addition, it snowed on 16 of the 31 days in the past month, so winter was unusually reluctant to loosen its grip.

Finally, on the last day of the month, though the temperature soared to 64 degrees — the first day at or above 60 since Nov. 10 — the state was visited by at least nine confirmed tornadoes.

Tornadoes in Green and Dane counties were EF1 tornadoes, with winds up to 100 mph. The others were EF0 tornadoes, with winds up to 80 mph. Some damage but no injuries were reported.

As we bid it adieu, we note that the month of March is distinguished by a couple of other meteorological oddities in our region. First, the greatest difference between the all-time warmest and all-time coldest temperatures for a calendar day in Madison is 88 and belongs to March 20 when in 2012 the high temperature was 81 degrees and in 1965 the low temperature was minus 7.

Along the same lines, if one compares the all-time warmest daily maximum temperature to the all-time coldest daily maximum temperature, the record difference is 72 on March 17 when the warmest high temperature was 80 in 2012 and the coldest high temperature was 8 in 1941.

These examples provide remarkable testimony to how variable the weather can be in southern Wisconsin around the time of the spring equinox. Here’s hoping for spring to finally make its presence known in April.

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, Meteorology, Seasons

Comments Off on Is March weather susceptible to being unusual?

How did Madison get a foot of snow on Saturday?

Posted on March 28, 2023 by WeatherGuys Editor

The 12.1 inches of snow that fell over Madison in the first nine hours of Saturday morning was surely a surprise to many residents while setting the all-time monthly record.

Forecasts made through the late afternoon on Friday, consistent with those made on Wednesday and Thursday, were suggesting that the heaviest band of snow would run southwestward from Racine/Kenosha back to northwestern Illinois and leave Madison with an inch or two.

GOES East Visible satellite imagery from March 25th paired with Day Cloud Phase distinction RGB imagery showing where the heaviest snow fell and a sharp cutoff where no snow occurred.

The forecast was in error not because the heavy snow band was not foreseen, but rather because the band ended up occurring farther northwestward than the computer forecast models had predicted.

This error underscores how hard it is to pinpoint the location of heavy precipitation bands in winter storms, especially rather weak winter storms like the one that hit on Saturday morning.

Even such weak storms have circulations that impact millions of square kilometers, while the precipitation bands impact only a small fraction of that area. In this case, the important structures and dynamics that conspired to produce the snow were well represented in the computer forecasts, but their location was different than the forecasted location for reasons that can be determined only in an after-the-fact investigation of the event.

Though much of the stunning progress in forecasting that has occurred in the past half century has been a result of relentless advances in theory, observational capabilities and the expanding power of computers, an often overlooked ingredient is the grueling detective work that ensues in the aftermath of such forecast errors. Meteorologists undertake “case studies” of such incidents to determine what physical factors were responsible for the weather as it actually occurred and also to better understand how and why the computer models went astray.

This difficult but necessary work informs the future development of these forecast models with the hope of minimizing future forecast errors. Thus, though such incidents as our Saturday snow might inspire the cynical view that weather forecasting is not a scientific endeavor, the exact opposite is actually true.

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

Comments Off on How did Madison get a foot of snow on Saturday?

What is the spring equinox?

Posted on March 20, 2023 by WeatherGuys Editor

The spring equinox marks the beginning of the spring season in the Northern Hemisphere. Also called the vernal equinox, it is the time of year when the sun rises due east and sets due west, no matter where you live. Earth’s axis of spin is tilted at an angle of 23.5 degrees from its orbital plane and always points to the North Star. The orientation of Earth’s axis with respect to the sun changes throughout the year and is the fundamental cause of our seasons.

On the equinoxes, the axis is not pointed at or away from the sun. This results in all areas on Earth experiencing 12 hours of direct sunlight. On the equinox and at the equator, the sun appears directly overhead at noon.

Satellite view of Earth on March 20th 2023, Spring Equinox in the Northern Hemisphere.

The equinoxes occur when the sun’s rays strike the equator at noon at an angle of 90 degrees. During the spring and fall equinoxes, the sun is above the horizon for all locations on Earth for 12 hours. During the vernal equinox, the sun is moving from south to north as it crosses above the equator.

For a long time, people have marked the changing of seasons and the sun’s track across our skies. Stonehenge was constructed in a way that marks its relation to the Sun’s position in the sky and in different seasons. At Machu Picchu, stones mark the four cardinal directions so that exactly at noon on the equinox, no shadow is cast. In Chaco Canyon, the ancestral Puebloan people carved spiral designs into rock that track the seasons.

The sun crosses the equator today at 4:24 p.m. Central Daylight Time, a good time to go outside and celebrate the event.

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

Comments Off on What is the spring equinox?

How are storm warnings defined?

Posted on March 13, 2023 by WeatherGuys Editor

Weather watches and warnings are issued by the National Weather Service under specific weather conditions.

A watch means that you should be aware that a weather hazard may develop in your area. A warning message is when the hazard is developing in your area.

When a warning occurs, you should take immediate action as suggested by the NWS. Warnings are based on observations of hazardous weather and are thus often issued for smaller areas. An advisory is a less urgent statement issued to raise awareness of a coming weather event that may cause some inconvenience.

As for winter storms, the NWS defines the following:

  • Winter storm watch: A watch means that severe winter conditions, such as heavy snow or ice, may affect your area, but where, when and how much snow are still uncertain. A watch is intended to provide enough lead time for you to prepare and thus is issued 12 to 36 hours before the predicted event.
  • Winter storm warning: The NWS issues a warning when there is a forecast of a significant winter weather event including snow, ice, sleet, or blowing snow, or a combination of these hazards that exceed locally defined criteria.
  • Winter weather advisories inform you that winter weather conditions are expected to cause significant inconveniences that may be hazardous. If caution is exercised, advisory situations should not become life-threatening.
  • Blizzard warnings: These let you know that snow and strong winds will combine to produce a blinding snow (near zero visibility), deep drifts and life-threatening wind chill.
Weather Guy Steve Ackerman (3rd from right) attended the UW-Madison StormReady ceremony in 2015. UW Chancellor Becky Blank is holding the StormReady sign with NWS Director Louis Uccellini. The designation of the University was a collaborative effort by UW Emergency Management, Campus Police, CIMSS, SSEC, AOS, and the NWS.

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: Severe Weather, Weather Dangers

Comments Off on How are storm warnings defined?