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Category Archives: Phenomena
What causes the Santa Ana winds?
Santa Ana winds are dry, warm, and gusty winds that blow from the interior of southern California toward the coast and offshore. They are a type of downslope wind, which is a wind directed down a slope produced by processes larger in scale than the slope.
Santa Ana winds can occur when the pressure gradient caused by a high-pressure region over the Rockies, in combination with friction, forces air from the mountainous West down the San Gabriel Mountains in southern California.
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Why are clouds relatively flat on the bottom?
Most clouds, especially those with flat bottoms, form in rising air. The air can be forced to rise due to convection, frontal lifting, or when air near the surface flows together from different directions. As a volume, or parcel, of air rises, it expands and cools. In addition, the relative humidity of the rising air increases. As the parcel approaches the point of saturation, water vapor condenses to form tiny water droplets or ice particles, creating a cloud. Saturation occurs at a distinct altitude, which varies depending on the temperature and humidity structure of the atmosphere. Below this condensation level clouds do not form.
Often low clouds, like stratus and cumulus, appear to have flat bases. These clouds form as air near the ground is rising. As the air rises, it expands as pressure decreases with altitude. This expansion results in a cooling, which causes the relative humidity in the rising parcel to increase. The temperature of the rising air approaches the dew point temperature. When it reaches the height where those two temperatures are equal, the relative humidity is 100% and a cloud forms. Meteorologists call this altitude the lifting condensation level. Continue reading
How does factory exhaust contribute to snowfall?
An article in the Wisconsin State Journal reported that on November 26, 2024, a factory near Menomonie, Wisconsin contributed to a narrow band of snow that extended for nearly 100 miles. This can occur only with certain atmospheric conditions. A … Continue reading
What is a meteorological bomb?
Storm systems that form in middle or high latitudes, in regions of large temperature contrast are called extratropical cyclones. This contrasts with tropical cyclones, such as hurricanes, which form in regions or relatively uniform temperatures.
Extratropical cyclones are surface low-pressure systems where the air at the surface flows counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. The winds around these centers of low-pressure spiral inward at the surface, forcing rising motions. The rising air can result in clouds and precipitation. The process of extratropical cyclone development and intensification is referred to as cyclogenesis. In North America there are favorable regions for cyclogenesis, including the eastern slopes of mountain ranges, the Atlantic Ocean off the Carolina Coast, and the Gulf of Mexico. The jet stream also influences cyclogenesis. Continue reading
Science-based policy is shrinking ozone hole
The Southern Hemispheric ozone hole usually begins to develop in mid- to late August, as the hemisphere emerges from its winter, and peaks in mid-October.
This year it first appeared closer to the end of August and by mid-September was 18.48 million square kilometers in size, smaller than in recent years, including both 2022 and 2023. Though this year’s slow start does not necessarily reflect a recovery of the ozone layer, it does support the notion that expert guidance has made a positive contribution to this vexing problem. Continue reading
