Do weather radars detect more than precipitation?

Posted on September 30, 2024 by WeatherGuys Editor
Scientists can distinguish rainy weather as seen to the west and north in graphic from flocks of birds because they appear as circles or blobs on radar screens. Most migratory birds take off from daytime resting and refueling habitats at sunset for their nightly journey. (Image credit: National Center for Atmospheric Research)

Yes. Radar, an acronym for RAdio Detection And Ranging, consists of a transmitter and a receiver. The transmitter emits radio wave pulses outward in a circular pattern.  Objects scatter these radio waves, sending some energy back to the transmitting point where it is detected by the radar’s receiver. The intensity of this received signal indicates the size and density of the suspended objects, such as precipitation. The time it takes for the radio wave to leave the radar and return indicates the distance.

Radar is designed to detect precipitation intensity and type, but it can detect living things as well. Flying insects in huge numbers can reflect enough energy back to a radar site to be detected. As an example, mayflies emerge in summer in enormous numbers around the Mississippi River between Wisconsin and Minnesota and are often detected by the weather radar in La Crosse, WI.

Some bird species gather at large communal roosting sites, particularly during their migration. The birds can be seen on radar as a flock takes off in the early morning. The flock appears on radar as an expanding, fading ring until they either fly above or below the radar beam and are no longer detected. Their signature often appears on radar during the morning departure, but not in the evening when they return. This is because atmospheric conditions affect the radar beam path. The beam is bent slightly downward in early morning due to a temperature inversion that often develops in the lower atmosphere. This departure in the path allows the radar to detect objects at lower altitudes more easily. During the evening, temperature inversions are weaker or non-existent and the beam bending doesn’t occur, inhibiting detection.

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

Category: Phenomena, Seasons

Comments Off on Do weather radars detect more than precipitation?

What is “The Old Farmer’s Almanac” forecast for winter?

Posted on September 23, 2024 by WeatherGuys Editor

“The Old Farmer’s Almanac” recently published its 2024-25 winter forecast. For the Upper Midwest region, it predicts winter will not be as cold as usual. The precipitation and snowfall forecast are for below average.

NOAA’s Seasonal Temperature Outlook for Dec-Jan-Feb 2024-2025, showing the effects of La Niña (Image credit: NOAA/Climate Prediction Center)

But don’t count on that forecast, as there is no proven skill. “The Old Farmer’s Almanac” does not share how it makes its forecast, so it cannot be judged scientifically. “The Old Farmer’s Almanac” also makes a weather forecast for specific time periods in a given season. Such detailed forecasts can be announced but are not trustworthy scientifically.

Seasonal weather forecasting is a science challenge. The National Oceanic and Atmospheric Administration’s Climate Prediction Center also makes seasonal forecasts. It explains the underlying principles of its forecast and provides validation of the forecasts publicly (see https://www.cpc.ncep.noaa.gov/products/predictions/long_range).

These modern day seasonal forecasts rely on known relationships between climate and some key forcing mechanisms, such as the El Niño. An El Niño is a periodic warming of the equatorial Pacific Ocean between South America and the international date line. This warming is a natural variation of the ocean and is used to predict departures from average conditions rather than to make specific weather forecasts. For example, a year with a strong El Niño leads to less snowfall than average in Wisconsin. These seasonal forecasts also take into account the climatic impacts of other global oscillations uncovered by the research of atmospheric scientists.

El Niño Southern Oscillation-neutral conditions are present, as equatorial sea surface temperatures are near to below average in the central and eastern Pacific Ocean. A La Niña watch is in effect, as La Niña is favored to emerge in September-November (71% chance) and is expected to persist through January-March 2025. Wisconsin winters tend to have more precipitation and near-average temperatures during a typical La Niña.

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

Category: Climate, History, Seasons

Comments Off on What is “The Old Farmer’s Almanac” forecast for winter?

Do oceans have heat waves?

Posted on September 16, 2024 by WeatherGuys Editor

As with the atmosphere, oceans can experience heat waves. The National Weather Service defines an atmospheric heat wave as a period of abnormally hot weather generally lasting more than two days. To be considered a heat wave, the temperatures must be outside the historical averages for a given area.

The magnitude of marine heatwaves (MHW) in the past 30 days is calculated using the daily high-resolution sea surface temperature (SST) dataset hosted at NOAA’s Physical Sciences Laboratory. (Image credit: NOAA/PSL)

Marine heat waves are defined as any time the ocean temperatures are warmer than 90% of the previous observations for the region at a given time of year. Marine heat waves can last for weeks, months and even years.

Marine heat wave conditions are monitored and forecast by NOAA. The National Data Buoy Center collects and disseminates quality-controlled marine observations. Global ocean surface temperatures are also monitored using satellite observations. In July 2024, 35% of the global ocean experienced marine heat waves.

The world’s oceans are heating up. Processes like marine heat waves and El Niño/La Niña make it a challenge to untangle the causes of warming anomalies for a specific year or region. However, analysis of the ocean temperature over decades shows the warming trends result from the observed increases in atmospheric carbon dioxide, just like the observed warming trend in atmospheric temperatures.

Warmer waters influence atmospheric weather patterns, such as tropical storms. There are also impacts on marine ecosystems.

An unprecedented marine heat wave dominated the northeastern Pacific from 2013 to 2016. Called “the Blob” because of the large expanse of unusually high temperatures, it upended ecosystems across a huge swath of the Pacific Ocean. The warm temperatures attracted subtropical species rarely seen off the West Coast of the U.S. The krill that humpback whales typically feed on grew scarce, and they switched to feeding on high concentrations of anchovy. The higher temperatures fueled a record bloom of toxic algae that shut down West Coast crabbing from November 2015 through March 2016.

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

Category: Climate, History, Seasons

Comments Off on Do oceans have heat waves?

Is the Sun Playing a Role in the Earth’s Global Warming?

Posted on September 9, 2024 by WeatherGuys Editor

The sun helps maintain Earth’s climate to be warm enough for us to survive. Even subtle changes in Earth’s orbit around the sun have led to and ended past ice ages. This relationship between Earth’s climate and its orbit around the Sun is well known.

The Solar & Heliospheric Observatory (SOHO), is a project of international collaboration between ESA and NASA to study the Sun from its deep core to the outer corona and the solar wind. (Photo credit: NASA/SOHO)

The sun’s activity and appearance goes through cycles, with one solar cycle taking 11 years to complete. The current cycle began at the end of 2019 and will reach peak levels of activity in 2025. During a solar cycle, the amount of solar radiation reaching Earth varies.  These changes have a variety of effects on Earth’s atmosphere, including auroras.

The amount of solar energy Earth receives follows the sun’s natural 11-year cycle of small ups and downs with no net increase since the 1950s. During this same time period, our global temperature has increased over 0.8 degrees C. This warming of Earth over the last few decades is too rapid to be caused by the observed solar activity.

Greenhouse gases in the atmosphere raise the surface temperature through absorption of radiation at wavelengths Earth emits to space. These gases play a crucial role in Earth’s climate by affecting our energy budget. They warm the planet. The three most abundant greenhouse gases in Earth’s atmosphere are: water vapor, carbon dioxide, and methane.

Humans have been altering weather and climate on local and regional scales for centuries. One of those impacts is through activities that increase the concentrations of greenhouse gases. Since the beginning of the Industrial Revolution, human activities have increased atmospheric carbon dioxide amounts by over 50% and methane levels by 150%. These rates of increase align with the observed trends in global warming.

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

Category: Climate, History

Comments Off on Is the Sun Playing a Role in the Earth’s Global Warming?

How can the Upper Midwest get such high dew points every year?

Posted on September 3, 2024 by WeatherGuys Editor

The dew point temperature is a measure of the amount of water vapor in the atmosphere and is also a good way to tell how uncomfortable you might feel on a hot day. Hot days and high water vapor contents are a serious health risk for some. Also, high water vapor content is a key fuel for severe thunderstorms.

There are three primary sources of water vapor that address this question: advection of water vapor largely from the Gulf of Mexico, evaporation over the Great Lakes, and transpiration from corn fields. The contribution from the Great Lakes in summer is minimal in comparison to the other factors, except maybe near the shorelines.

The process of evapotranspiration. Corn tends to release more vapor because it is a taller plant and tends to use more water than most crops. (Image credit: USDA)

Southerly winds help bring warmer temperatures to the Upper Midwest but they also transport moisture from the Gulf of Mexico. This leads to higher dew points over Wisconsin and the Midwest. Studies have demonstrated that summertime precipitation in the Midwest is strongly correlated with the strength of this Great Plains low-level jet stream, which transports relatively warm, moist air northward from the Gulf of Mexico.

Transpiration is the release of water vapor from plant leaves. Transpiration has three main steps: the plant’s roots uptake water from the soil, the water moves through plant tissues, and the leaves release water vapor into the air through their stomata. During summer months, maturing cornfields become a huge source of water vapor to the atmosphere. Studies suggest a single acre of corn can transpire 3,000 to 4,000 gallons of water per day. On calm days, an analysis of dew points over the Midwest can identify the location of the Corn Belt. This transpiration by corn is sometimes referred to as “corn sweat.”

Together, these factors can result in summer dew points in the low to middle 70Fs for the Upper Midwest.

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

Category: Climate, Phenomena, Seasons

Comments Off on How can the Upper Midwest get such high dew points every year?