GALWAY, IRELAND- Irish weather researchers report a number of new observations on the nature of the little understood phenomenon of drizzle.

Professor Gerard Jennings of University College Galway, Ireland, has been studying drizzle for the past year in one of the dampest places in a very wet country, Mace Head on the Atlantic coast of Ireland. This is one of the westernmost spots in all of Europe.

Dr. Jennings chose an ideal place to study the phenomenon of drizzle, that fine, soft rain where you don't know whether it's raining or the moisture is just hanging in the air. The west coast of Ireland gets its air (and rain) freshened by a 3,000 mile journey across the Atlantic Ocean and is therefore virtually pollution-free.

Working at the University College Galway Atmospheric Research Center at Mace Head, Dr. Jennings and a colleague used specially coated slides to take imprints of drizzle drops. From these imprints they were able to calculate the size and water content of the droplets. They found that drizzle drops contain about 0.02 grams of water per cubic meter, about a tenth of the level found in a cloud. Furthermore they found that the average drizzle drop is about 0.2mm in diameter, whereas the average raindrop is ten times that size.

"The drops are so light, much smaller than ordinary rain, that they just say in suspension in the air. There isn't enough water to trigger the standard rain gauge, so it's quite difficult to measure," noted Dr. Jennings.

The creation of drizzle is a complex process. It is influenced by temperature and humidity and whether there are specks of dust for the water to condense on. Upward drafts of air also affect drop size because this causes the drops to collide and coalesce, he noted.

"The next step in the study will be to analyze the chemistry of drizzle to see if it is washing pollutants out of the air. We get acid rain, so we think there may also be acid drizzle," he said.

The drizzle studies should contribute to the understanding of various meteorological processes. The techniques developed in these studies should also be useful for studies of irrigation and water spraying.

SOURCE: Internet-eireann.

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