March 31, 2009
Good Air Quality across U.S.; Meteorology Minute on Synoptic Patterns; Central American Burning Season Gets Underway
Air quality is mostly Code Green (Good) across the nation today, as shown by the loop of PM2.5 AQI values (below); ozone levels are all in the Code Green range today as well.
Today’s meteorology minute is brought to you by synoptic patterns, specifically extratropical cyclones (not to be confused with tropical cyclones, which are hurricanes or typhoons). An extratropical cyclone is a big low pressure system that occurs over land in the mid-latitudes; they generally travel from west to east across the continental U.S. and often produce large amounts of precipitation (snowstorms) and extreme weather events (tornadoes, thunderstorms). The life cycle of a typical extratropical cyclone follows a predictable pattern, called the Norwegian Cyclone Model, after the Norwegian meteorologists Vilhelm and Jacob Bjerknes, who first described cyclogenesis in the early 1900s. This pattern-like quality of weather systems is particularly evident today, looking at the MODIS Terra true color image of the eastern U.S., overlaid with the current AQI values and synoptic analysis (below). Extratropical cyclones display a very distinctive structure that is evident in satellite imagery. The satellite image and synoptic pattern today are almost exactly the same as last Tuesday (take a look at my post from March 24). They are so similar that when I pulled up today’s satellite image, I thought I had opened last week’s image by mistake. An occluded low pressure center is located over the Northern Plains, with the associated cold front running north-to-south along the center of the country. There is even a characteristic “dry slot” between the occluded front and the low pressure center. And just like last week, high pressure is anchored over eastern Virginia, bringing clear skies and good air quality to the Mid-Atlantic. Weather and air quality forecasters rely on synoptic patterns, which lead to predictable weather/air quality outcomes that aid in forecasting (e.g., clear skies, low dew points, cooler conditions, good air quality following a cold front; thunderstorms ahead of a cold front; high dew points, warm conditions, and often poor air quality in the warm sector of the system). Today’s extratropical cyclone is a major spring snow storm that is causing blizzard conditions across the Dakotas and into Minnesota, which is not good news for the folks trying to deal with flooding of the Red River and other waterways in the region.
The big air quality story today is in Central America, as the spring agricultural burning season is getting underway. Today’s NOAA Hazard Mapping System (HMS) Fire and Smoke product (below) shows the many fires across Central America and the Caribbean.
True color images for Central America are slow in coming into today, but particulates due to smoke from the fires are evident in AOD imagery. Today’s MODIS Terra AOD image for the U.S. from IDEA (below on left) indicates elevated AOD in the Gulf of Mexico, southern Texas, and northern Mexico from the agricultural fires. The 14:45 UTC GASP image for Central America, courtesy of Hai Zhang, Shobha Kondragunta and NOAA NESDIS (below on right), shows high AOD readings over the Yucatan peninsula and southern Gulf of Mexico associated with the fires. Although these smoke plumes are not impacting air quality in Texas or the Gulf Coast states today, they likely will in the days ahead as the smoke plumes spread into the U.S.; we will monitor the plumes on the Blog and keep you updated.
 |  |