Understanding ENSO

Improve your understanding of the El Niño and La Niña and their impacts on our climate and weather with BoM's new Understanding ENSO video
This video explains what El Niño–Southern Oscillation (ENSO) is, how the cycle works including the science behind the phases, and the potential impacts on Australia’s climate and weather.

Essentials of Meteorology

Essentials of Meteorology - An Invitation to the Atmosphere

C. Donald Ahrens

I taught an online class this semester on meteorology, and this was the textbook I was given. I always hold my breath a bit concerning textbooks, because I've taught chemistry, physics, cell biology, and meteorology...and my background includes two degrees in neuroscience. I never stop reading. As a deaf person who doesn't listen to music, go to movies, or watch television much, reading is my source of relaxation as well as involved in my work. I tend towards either nonfiction or classical literature lately, and much of my reading involves science and specifically weather. Global warming is such a hot topic now, and I've wanted to stay on top of this also because of my interest and ethical work as concerns deaf people in catastrophic occurences.

Anyway, this was definitely one of the better textbooks. My students didn't start having problems until the fifth and sixth chapters, which were way too technical on air pressure and wind for an online course and for students who were taking this class with no prior physics. Since physics is deeply involved in weather science, it would have been much easier to teach those chapters in a classroom, though I am now exploring avenues to teach these very things online.

I felt that the author of this textbook was speaking to the students this time instead of writing to his peer group (which is how many textbook and journal articles write today). The information is interesting, and thorough, and the textbook can definitely be adapted to younger classes or beginning science classrooms. It would just take some time to adapt it better and unfortunately, the university I taught at just changed their online program which everyone was required to learn at the same time they were expected to also do classwork. I also had to cut down the amount to be learned because it was an eight week course, instead of a semester course. That also complicated things...but I thought on the whole this was a good book, and I am continuing to read the rest of it for my own personal understanding.

(Karen L. Sadler - Pittsburgh, PA)

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Doppler radar can detect more than just weather

Doppler weather radar has become ubiquitous in today’s American culture as people seek to stay updated on weather conditions from home, from their cell phone, and while on the road. But on calm weather days, meteorologists have time to examine some of their tools and instruments with a different eye.

While doppler weather radar is traditionally used to detect water and ice droplets in the sky - otherwise known as clouds and precipitation - weather radar has also been shown to detect birds, buildings, vehicular traffic, airplanes, and even the smoke from the collapsing World Trade Center towers and the disintegration of the Space Shuttle following the 2003 Shuttle Columbia disaster.

Speeding Traffic?

Take, for instance, the case of the National Weather Service doppler radar located just outside of Chicago, Illinois. On August 12, 2008 the local doppler radar was able to detect traffic flowing on Interstates 55 and 57. When a low-altitude layer of warm air developed over the region, the radar beam was refracted lower to the ground than normal. The result was the radar beam being bounced off of vehicles along the area interstates. (Click each image for a larger view).

What sets doppler radar apart from first-generation traditional radar tools is that doppler radar can detect velocities; that is, it can detect the speed at which droplets are moving toward or away from the radar site. Not only does the radar detect the presence of the vehicles, but also their velocities. When the radar is switched into velocity mode, the display shows red and green shades - green representing movement toward the radar and red representing movement away from the radar site:

When keyed to the green and red shades represented in the image above, the radar indicates some traffic was flowing as fast as 115 knots (130mph). The National Weather Service, however, states that this may simply be “noise” - false radar returns - rather than someone actually driving that fast.

Bats

When bats congregate in large swarms, their volume can reflect the radar signal in sufficient strength to be detected by the radar tower, as shown in this image (which also displays a supercell thunderstorm) from the Storm Prediction Center, taken over Texas in 2006:

The National Weather Service has archived a loop of radar images of the above even displaying a supercell thunderstorm swallowing a swarm of bats.

Birds and Migrations

The National Weather Service out of Green Bay, Wisconsin captured an amazing set of images displaying a large group of birds leaving from Green Island on the morning of August 10th, 2006:

Research is being done on how radar may actually be useful in tracking certain migratory species over large distances: Radar technology - A tool for detecting migratory aerofauna.

Space Shuttle Columbia Disintegration

In February of 2003, the Space Shuttle Columbia disintegrated on re-entry as it attempted to land in Cape Canaveral, Florida. As the shuttle broke apart in the upper atmosphere, weather radar towers in the southern states detected the debris streaming through the atmosphere late that morning, as shown in this image from the Shreveport, LA National Weather Service office on the morning of February 1st, 2003:

The National Weather Service has compiled an in-depth archive of the Shuttle Columbia Diaster.

September 11th Attacks

Following the collapse of the World Trade Center towers in New York City as a result of the terrorist attacks of September 11th, 2001, the New York City radar detected the plume of smoke slowly rising over New York City that morning (click image for larger view):

Sunrises and Sunsets

Whenever the sun gets low in the sky - at sunrise or sunset - its electromagnetic energy can wreck havoc with a doppler radar receiver. When the energy is received by the radar site, the algorithms often display this energy as a “spike” on radar. The images below are from the Twin cities radar site in Chanhassen, Minnesota. Interestingly, the spike changes position with the seasons. Click each image for a larger view:

Winter: When the sun sets South of due West in the winter, the “sunset spike” indicates as much:

Summer: When the sun sets North of due West:

Finally, when the sun rises and sets due East and West, respectively, the radar spike reflects that direction as well - an event that occurs twice each year - the first day of spring and the first day of fall:

Spring and Fall:

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More Information:

• To view your local doppler radar image, visit the National Weather Service Radar page.
• If you have more interesting radar images to share, please post in the comments.

La Niña Draws to a Close

The 2008-2009 La Niña has drawn to a close and the Climate Prediction Center has officially called an end to the continued monitoring of this year’s event.

The 2008-2009 La Niña has drawn to a close. Image indicates sea surface water temperatures (top) and the departure from the average sea surface temperature (bottom). La Niña is indicative of cooler than normal (blue). The lack of a significant temperature anomaly in the equatorial Pacific indicates to scientists that this year's La Niña has come to an end. Image Source: NOAA

La Niña (Spanish for “the little girl”) is the term used to describe the period when the sea surface temperatures of the equatorial Pacific ocean are cooler than normal. This region of the ocean tends to waiver between periods that are warmer than average (referred to as “El Niño”) and warmer than average - La Niña . In between these extremes are relatively neutral periods where sea surface temperatures are within a degree or two of average. It is this neutral period that the Climate Prediction Center is indicating is now imminent.The end of the current La Niña indicates that the Pacific Northwest may begin to dry out and the south may return to near-normal rainfall patterns.La Niña tends to bring nearly opposite effects of El Niño to the United States — wetter than normal conditions across the Pacific Northwest and dryer and warmer than normal conditions across much of the southern tier. The impacts of El Niño and La Niña at these latitudes are most clearly seen in wintertime. In the continental U.S., during El Niño years, temperatures in the winter are warmer than normal in the North Central States, and cooler than normal in the Southeast and the Southwest. During a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest.It is unknown precisely when El Niño will return.

New Wind Farm Causing Problems for Doppler Radar

A relatively new wind energy farm in central Wisconsin has created a newly-discovered, puzzling side effect: interference with the local National Weather Service doppler radar.The Butler Ridge wind farm was constructed in February of this year and contains a total of 36 wind turbines, each standing about 300 feet above ground level. These windmills were build on a ridge line that is about 1100 feet above sea level, placing the turbines in an optimal location to benefit from the highest wind speeds in the region. Coincidentally, the location is in the sight of the local doppler radar tower in Sullivan, WI that is approximately 30 miles south of the wind farm.
Doppler radar functions to detect atmospheric phenomena by sending out an electromagnetic signal and simultaneously “listening” for the signal to return if it is bounced off of an object. Many objects will reflect the radar beam, most notably rain droplets, ice crystals, and snowflakes. But as we reported earlier this year, doppler radar can also detect bats, birds, aircraft, surface traffic, and even tragedies like 9/11 and the Columbia disaster. They are even believed to have the potential to alter the weather.In the case of the Butler Ridge wind farm, the radar beam is being reflected by the large blades on the spinning turbines. This electromagnetic energy is then reflected back to the radar dome and the radar detects the object. The turbine blades then appear on the radar image. This seemingly innocuous interference could have significant ramifications in the upcoming severe weather season though.

Doppler radar is arguably one of the most critical tools at the disposal of the National Weather Service when they look to provide timely watches and warnings of severe thunderstorms and tornadoes. By examining the output of doppler radars, meteorologists are able to detect and forecast thunderstorms that may become severe and where they may track. But if the radar image is masked by interference such as the wind turbines, it is feared that severe weather watches and warnings may be less robust.The National Weather Service Radar Operations Center has enlisted the help of the wind energy industry to try to alleviate these problems in the future by locating the wind farms in places that would not interfere with such radar signals. They have published anextensive analysis of the problem. The map below displays the locations (in red) of the doppler radar sites that may be impacted. The yellow regions are those in which the radar beam travels close enough to the ground that it could be impacted by windmills constructed in those regions.
Meteorologists may be able to write software code that is able to filter out this interference, but such work can be costly and time-consuming. The primary concern is that filtering the data to remove such interference may also increase the risk of filtering out true radar echoes - those of actual storms that must be detected for public safety.With the mushrooming popularity of wind energy around the country, this problem is one that is sure to warrant further study and creative mitigation attempts.

This map displays the locations of all National Weather Service radar locations (red) and the regions in which the radar beam is low enough to the ground that it may be impacted by windmills (yellow). Credit: NOAA