Variation with Height and Latitude of Radiosonde Temperature Trends in North America, 1975–94

Abstract

Based on the 120-station North American radiosonde network, temperature trends for 100?50-mb (low stratosphere), 300?100-mb (tropopause), and 850?300-mb (troposphere) layers, and Earth?s surface, are evaluated for six 10° latitude bands extending from 20°?30°N to 70°?80°N for the 20-yr interval 1975?94. Confidence estimates are indicated by two standard errors of the least squares regression. In the average for the six latitude bands, the 100?50-mb annual temperature trend is ?0.5°C decade?1 and the 850?300-mb trend is 0.2°C decade?1. In spring at 70°?80°N, the 100?50-mb and 300?100-mb layers cool by almost 2°C decade?1. The 300?100-mb layer cools by 0.7°C decade?1 relative to the 850?300-mb layer at 70°?80°N, but the two layers have the same warming trend at 20°?30°N, indicating the transition from the 300?100-mb layer being mostly in the stratosphere in polar regions to mostly in the troposphere in the northern subtropics. The surface warms much more than the troposphere at 70°?80°N (showing that surface temperature trends are not representative of tropospheric trends in polar regions) and slightly more at 20°?30°N, but surface warming is less than tropospheric warming in the 40°?70°N belt. At the surface at the radiosonde sites the 1200 UTC (morning) temperature cools relative to the 0000 UTC (evening) temperature by 0.05°C per decade on average, but the 850?300-mb temperature trends at 0000 UTC and 1200 UTC are essentially the same. The 0.7°C decade?1 cooling of low stratosphere relative to troposphere increases to 0.9°C decade?1 when adjustment is made for the stratospheric warming and tropospheric cooling following El Chichon and Pinatubo eruptions. The temperature trends obtained from 11 North American radiosonde stations in a 63-station global network agree well with the trends based on the entire 120-station network, and the latter are fairly representative of zonally averaged trends based on the 63-station network and microwave sounding unit data. Comparison with Canadian ozonesonde data shows that, in the low stratosphere and high troposphere during 1975?94, a decrease in temperature of 1°C decade?1 was associated with a decrease in ozone of about 10% decade?1.