Dear Tom,
Watching the daily temperatures from Baghdad, I wonder why, in the desert, it gets so warm during the day and so cool at night.
Bonnie Zon
Dear Bonnie,
A large range between the day’s high and low temperatures –the diurnal range–is a particularly noteworthy feature of desert climates, and it’s mainly the result of the thermodynamic characteristics of dry air.
Water vapor has a great capacity to hold heat energy–it has a high specific heat. That means when a given amount of heat energy is applied to (or removed from) dry air, its temperature will rise (or fall) more than humid air. When the air over a region is predominantly very dry, as it is in desert areas, the climate is relatively cloud-free, precipitation and vegetation are sparse and the soil is rocky or sandy. All those are conducive to large diurnal temperature ranges.
———-
Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.
Write to: ASK TOM WHY, 2501 Bradley Place, Chicago, IL 60618 or asktomwhy@wgntv.com (Mail volume precludes personal response.)
