The Weather Guys

We are not sure we can, but we have always wanted to do so! In the past, people rang bells or fired cannons to prevent lightning or cause rain — producing sound and fury but nothing in the way of success.

The scientific era of weather modification took hold in the 1940s and ’50s with the advent of cloud-seeding experiments. In cloud seeding, airplanes drop particles of dry ice or silver iodide into clouds with temperatures below freezing. These particles are very effective in generating ice particles, with the hope of increasing the amount of rainfall or snowfall.

However, progress in cloud seeding has been slow as the processes are poorly understood. Not only that, these experiments aren’t reproducible in the sense that we can never really know if a seeded cloud would not have precipitated on its own, without assistance.

Farmers have long sought a way to suppress hail. One hailstorm can destroy a year’s crops in a few minutes. Cloud seeding during the early stages of cumulonimbus development is thought to encourage a reduction in hail damage by keeping hailstone sizes small, but again, the results have been mixed.

Another active area of weather modification has been fog dispersal. Fog can shut down an airport for hours, causing delays with negative economic impact. Like clouds, fog can be seeded with materials that cause the water droplets in fog to turn into ice, which then precipitates out, dispersing the fog. While a practice at many airports worldwide, it is impractical to apply over large regions.

Humans have changed the atmosphere in many ways. These changes usually come about as unintended byproducts of modern civilization. So far, humans have been more effective at modifying weather and climate by mistake than by design.

The jet stream is a ribbon of high wind speeds near the top of the troposphere (about 6 miles above the surface of the Earth). The major jet streams flow west to east. The existence of fast winds moving from west to east was long suspected because of the movement of storms, cloud systems and volcanic debris high in the atmosphere.

Suspicions remained unconfirmed until World War II. During major U.S. air raids against Japan, the B-29 airplanes flew from east to west at altitudes of 10 kilometers, where they encountered a strong stream of westerly winds that slowed or even stopped the planes in mid-air. There were also balloon observations made in the early to mid-1920s by Wasaburo Ooishi, the first director of Japan’s upper-air observatory, that suggested these fast moving winds.

Today’s weather reports often discuss the position of the jet stream. The jet stream position is strongly tied to the southern edge of the dome of cold air centered on the North Pole. During the depths of winter, that cold dome expands considerably, extending nearly to the Gulf of Mexico. As the winter ends and spring approaches, the hemisphere begins to warm up and the cold dome shrinks dramatically. Its southern edge moves to central Canada by early summer.

The jet stream is associated with vigorous upward and downward vertical motions. The upward vertical motions are instrumental in producing thunderstorms. Thus, when the jet stream migrates northward as the weather warms in spring/summer, so does the greatest concentration of severe weather outbreaks. That season is heading our way, denoted by designating this week as Tornado and Severe Weather Awareness Week, with a drill day planned from 1 to 2 pm. on Thursday.