The Weather Guys

What is a ‘bomb cyclone’?

Posted on January 8, 2018 by WeatherGuys Editor

Vehicles move along a snow and ice covered Interstate 26, near Savannah, Ga., Wednesday, Jan. 3, 2018. A brutal winter storm dumped snow in Tallahassee, Fla., on Wednesday for the first time in nearly three decades before slogging up the Atlantic coast and smacking Southern cities such as Savannah and Charleston, South Carolina, with a rare blast of snow and ice. (Photo credit: Robert Ray, Associated Press)

The term “bomb cyclone” refers to the formation and rapid development of a mid-latitude cyclone. A mid-latitude cyclone is a large-scale, low-pressure system, characteristic of the middle latitudes, that has counter-clockwise flow around its center (in the Northern Hemisphere).

A primary measure of development in these storms is a drop in the atmospheric pressure at the center of the storm. Air near the ground is forced to move inward to the center of the circulation — this is known as convergence.

In the upper levels of the atmosphere above the center of a developing mid-latitude cyclone there is divergence, the opposite of convergence. If the divergence of air above is stronger than the convergence of air near the surface, the surface pressure will fall and the mid-latitude cyclone will intensify.

If the barometric pressure of a mid-latitude cyclone falls by at least 1 millibar per hour for 24 hours, the storm is referred to as a “bomb.” A millibar is a unit of pressure that measures the weight of the atmosphere above you. The average sea-level pressure is about 1,010 millibars, so in a bomb cyclone about 2.3 percent of the atmosphere above is removed and moved someplace else.

Meteorologists have used the term ‘bomb cyclone’ for at least 50 years.

They are not rare events, as on average there are about 40 events each year in the Northern Hemisphere. As with any weather event, the number of bomb cyclones varies from year to year.

The recent storm on the East Coast was a bomb cyclone. It is also referred to as a nor’easter – a mid-latitude cyclone that affects the northeastern United States and extreme eastern Canada.

Category: Phenomena, Seasons, Severe Weather

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Did climate change kill the dinosaurs?

Posted on December 18, 2017 by WeatherGuys Editor

Landsat image of the Sudbury Basin in Ontario,
the remnants of an asteroid impact that
occurred ~1.8 billion years ago. Credit: USGS.

Sixty-six million years ago, the age of the dinosaurs ended abruptly, coinciding with the extinction of about 75 percent of the total number of living species.

Evidence and climate modeling indicate that global wildfires resulted from a collision with a massive asteroid that could have lofted large amounts of soot into the atmosphere. The smoke would have plunged Earth into darkness for nearly two years, which would have shut down photosynthesis, drastically cooled the planet, and contributed to the mass extinctions as evidenced in the fossil record.

It is now an accepted scientific fact that objects from outer space can and do collide with planets. The collision of the Shoemaker-Levy comet with Jupiter in 1994 provided spectacular evidence that extraterrestrial objects can affect a planet’s atmosphere.

Depending on its exact location, a major asteroid impact on Earth and the debris ejected by the impact can cause extended darkness due to global fires, acid rain, ozone loss and even mile-high tsunamis.

In 1990, evidence was discovered of an impact with an asteroid that occurred about 66 million years ago near the Yucatán Peninsula. Named for a local village, the Chicxulub crater is a 112-mile-wide impact crater visible in gravity and magnetic field data. The crater size is consistent with a 6- to 12-mile-wide asteroid.

Remnants of the asteroid have been found in sediments worldwide, confirming its global influence. The Chicxulub impact was probably not a once-in-history event. There are indications in the fossil record of other extinction events that occur every 26 million years or so.

Scientists are coming to the realization that on very long time scales the history of Earth, including its climate, may be periodically upset by asteroid and comet impacts.

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.

Category: Climate, Phenomena

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How are the National Weather Service and Wisconsin connected?

Posted on November 27, 2017 by WeatherGuys Editor

The roots of our National Weather Service have a distinctive Wisconsin flavor. Professor Increase A. Lapham, a University of Wisconsin professor at the time of the founding of the university, was the first official Smithsonian Institution weather observer in Milwaukee and long argued for the establishment of a national weather observation network.

With the election of President Ulysses S. Grant in November 1868, Lapham and Rep. Halbert Paine, the U.S. congressman from Milwaukee, thought the time was right to pursue this goal. Grant had developed a keen sense of the influence of weather on military operations through his experiences in the Civil War.

On Feb. 2, 1870, Paine introduced a Joint Congressional Resolution that tasked the Secretary of War “… to provide for taking meteorological observations at the military stations in the interior of the continent and at other points in the States and Territories … and for giving notice on the northern [Great] lakes … of the approach and force of storms.”

Congress passed the resolution with little hesitation and a week later, on Feb. 9, 1870, President Grant signed it into law – effectively establishing the first iteration of the National Weather Service (then called the U.S. Army Signal Service). Operation of the Signal Service began Nov. 1, 1870, and one week later, Lapham issued the first high wind warning for the Great Lakes from Chicago. The forecast was accurate and was credited with saving considerable property and protecting lives.

The Wisconsin connection to the National Weather Service continues to this day, as the current director of the NWS is a UW-Madison graduate, Dr. Louis Uccellini.

NWS Director Louis Uccellini awards ‘Storm-Ready’ plaque to UW-Madison Chancellor Becky Blank in 2015. Photo credit: Bill Bellon

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.

Category: Meteorology

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What’s happening with the ozone hole?

Posted on November 6, 2017 by WeatherGuys Editor

The ozone hole is a region where there is severe depletion of the layer of ozone — a form of oxygen — in the upper atmosphere that protects life on Earth by blocking the sun’s ultraviolet rays. (Photo credit: NASA)

Encouraging news arrived this week regarding the size of the Southern Hemisphere ozone hole. NASA reported that this year’s ozone hole (which peaked on Sept. 11 at 7.6 million square kilometers) was the smallest since 1988, just years after the problem was first identified.

Though a number of factors contribute to the annual size of the ozone hole, it is beyond doubt that the leading factor is the reduction of chlorofluorocarbons (CFCs), industrial chemicals long used for refrigeration among other things.

Just a few years after the ozone hole was detected via satellite, the industrialized nations of the world, meeting in Montreal in 1987, adopted what is known as the Montreal Protocol. That international agreement, based upon the consensus scientific understanding of the problem, placed prudent restrictions on the use of CFCs. The result of this scientifically informed policy-making has been a gradual but systematic healing of the ozone hole.

This should serve as a leading example of the power of scientific analysis and understanding to shape important environmental policy. The world is facing a slower burning crisis as a result of human-induced changes to the atmosphere that have, in turn, begun to change the climate.

There is no lack of scientific consensus of the roots of this problem nor any shortage of science-based prescriptions of seeking its remedy. The time has long passed for our society to seriously debate, and then begin to take, the bold actions necessary to meet this crisis. Our scientific and industrial infrastructure is more than sufficient to meet this pressing challenge — we have successfully done so before.

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.

Category: Climate, Phenomena

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Is there a net loss of water from the upper atmosphere?

Posted on October 16, 2017 by WeatherGuys Editor

Yes, but very little loss occurs.

GOES-16 satellite image of water vapor in Earth’s Atmosphere.

Our planet, along with all planets that have an atmosphere, lose gases to outer space.

The escape velocity is the minimum speed needed for an object to escape from the gravitational influence of Earth. The escape velocity is a function of how close the object is to Earth’s surface and the molecule’s mass.

Different processes drive this escape, and they operate at different time scales. One loss process is through molecular kinetic energy.

Temperature is a measure of the average kinetic energy of a gas. The collisions between molecules in that gas cause the velocities of individual molecules to gain and lose kinetic energy.

The kinetic energy and mass of a molecule determine its velocity. The more massive the molecule of a gas is, the lower the average velocity of molecules of that gas at a given temperature.

Therefore at the same temperature, it is less likely that heavier gases will reach escape velocity than lighter gases. Hydrogen will escape from an atmosphere more easily than carbon dioxide, which has more mass.

If the planet has a high mass, like Jupiter, the escape velocity is greater, and fewer particles will escape. Given Earth’s temperature and mass, our atmosphere does not lose a significant proportion of its atmosphere through molecules reaching escape velocities.

Stripping of the atmosphere by a solar wind is a process that can strip an atmosphere of its gases. Earth’s magnetic field helps to protect us from large losses by this process.