Geographical distribution of the vertical temperature profile trends derived from radiosonde observations

Long-term changes in the horizontal and vertical temperature profiles are an important component in the detection and attribution of climate change. Major efforts have been made to estimate the variations in the global-mean temperature at the earth surface and the lower to mid-troposphere using three sources of measurements: surface observations, satellite observations and radiosonde observations. Radiosondes have a distinct advantage over the other two in the vertical temperature profile change detection due to their high vertical resolution. Although there is agreement on the cooling trend of the stratosphere, the geographical distribution of the tropospheric trends is less well known. Using quality-controlled monthly mean radiosondes observations from the 50-year NCEP reanalysis archives, the vertical temperature profile trends from 1979-99 have been computed and classified into four categories: those displaying more warming in the lower troposphere than the upper troposphere (type LT), nearly constant warming trend throughout the troposphere (type CW), more warming at the upper troposphere than the lower troposphere (type UT), and mostly little change throughout the troposphere (type ZT). The geographical distribution of these four types of vertical profile trends is then examined. There are many stations of type LT in the high latitudes of the NH, and by contrast, relatively more stations of type UT in the high latitudes of the SH. In the Eurasian continent, most stations show more warming in lower troposphere than aloft (type LT), whereas type CW dominates over North America. In the tropics, where the density of rawinsondes is low, all four types are found, indicating that the average trend over the whole tropical area is not well defined from radiosonedes due to the spatial sampling problem.