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Bomb Cyclones | Earth Wise

December 2, 2021 By EarthWise Leave a Comment

It seems like we are hearing about new weather phenomena pretty frequently these days. One name that has popped up lately is “bomb cyclones.” Bomb cyclones, it turns out, are storms that undergo “bombogenesis.” What that means is a low-pressure area (in other words, a storm) that undergoes rapid strengthening and can be described as a weather bomb, or popularly, a bomb cyclone.

These things usually take place over remote tropical ocean areas but a really intense one struck the Pacific Northwest on October 24th. The storm off the coast of Washington, with a barometric pressure reading equivalent to a category 4 hurricane, was the second extreme low-pressure storm in the North Pacific in a single week. Both storms involved pressure drops of more than 24 millibars in 24 hours, making them bomb cyclones.

These storms brought high winds and extreme precipitation that doused wildfires and provided some relief to the extreme drought in Central and Northern California. Along with these positive effects, however, the storms also caused power outages, flooding, landslides, and mud and debris that washed out roads.

The October 24-25 event brought 16.55 inches of rain to Mount Tamalpais in Marin County, California in a 48-hour period. Sacramento got 5.44 inches of rain, breaking a 140-year-old record. And the city had just broken another extreme weather record for the longest dry spell in history.

The storms directed streams of moisture from north of Hawaii toward the West Coast in long, narrow bands of moisture known as atmospheric rivers. We are learning about all sorts of unfamiliar weather phenomena as extreme weather events become increasingly common.

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Extratropical Cyclones Drench West Coast

Photo, posted January 4, 2018, courtesy of NOAA/CIRA via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Dust From The Sahara | Earth Wise

July 9, 2020 By EarthWise Leave a Comment

A vast cloud of dust from the Sahara Desert blanketed the Caribbean in late June before drifting across the southeastern U.S. The phenomenon is nothing new; only the magnitude of the occurrence this time around was unusual. According to experts, this is the most significant Sahara dust event in 50 years.

The Sahara Desert is the major source on Earth of mineral dust, with some 60-200 million tons of it per year being lifted into the atmosphere. Convection currents over hot desert areas lift the dust to very high altitudes. From there, it can be transported worldwide by winds. The dust, combined with the extremely hot, dry air of the Sahara Desert often forms an atmospheric layer called the Saharan Air Layer, which can have significant effects on tropical weather by interfering with the development of hurricanes. The Saharan Air Layer typically moves across the North Atlantic every three to five days from late spring to early fall, peaking in the middle of the summer. It can occupy a layer as much as two miles thick in the atmosphere.

The dust plume this summer was highly visible from space, covering thousands of miles of the Atlantic Ocean and the Caribbean Sea.

A common effect of Sahara dust is that normally blue skies can acquire a milky haze, but beyond that can lead to spectacular sunsets. But apart from the visual spectacle, the dust can aggravate the conditions of people with asthma, respiratory illnesses, and allergies. On the positive side, as long as the dust is around, it is much less likely that tropical storms and hurricanes will form.

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Sahara dust blankets Caribbean, air quality hazardous

Photo, posted June 22, 2020, courtesy of Sagar Rana via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Predicting Lightning Strikes

November 19, 2019 By EarthWise Leave a Comment

Lightning is one of the most unpredictable phenomena in nature. Approximately 100 lightning bolts strike earth’s surface every second, and each lightning bolt can contain up to one billion volts of electricity. Lightning regularly kills both people and animals and sets homes and forests on fire. It’s also been known to ground airplanes.

Researchers at EPFL – a research institute and university in Switzerland – have developed a novel way to predict where and when lightning will strike. The system relies on a combination of standard data from weather stations and artificial intelligence to predict lightning strikes to the nearest 10 to 30 minutes and within a radius of less than 20 miles. The simple and inexpensive system was outlined in a research paper recently published in Climate and Atmospheric Science, a Nature partner journal.

According to researchers, the current systems for predicting lightning strikes are slow, expensive, and complex, relying on external data acquired by satellite and radar. The new inexpensive system from EPFL uses real time data that can be obtained from any weather station, meaning it can cover remote regions that are out of radar and satellite range and where communication networks are lacking. The quick predictions from the system allow alerts to be issued before a storm has even formed.

The system uses a machine-learning algorithm that’s been trained to recognize conditions that lead to lightning. The researchers took into account atmospheric pressure, air temperature, relative humidity, and wind speed, among other things. After training the algorithm, the system was able to predict lightning strikes accurately nearly 80% of the time.

This system is a simple way to predict a complex phenomenon.

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