MSU Tropospheric Temperatures: Dataset Construction and Radiosonde Comparisons

Two deep-layer tropospheric temperature products, one for the lower troposphere (T 2LT ) and one for the midtroposphere (T 2 , which includes some stratospheric emissions), are based on the observations of channel 2 of the microwave sounding unit on National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites. Revisions to version C of these datasets have been explicitly applied to account for the effects of orbit decay (loss of satellite altitude) and orbit drift (east-west movement). Orbit decay introduces an artificial cooling in T 2LT , while the effects of orbit drift introduce artificial warming in both T 2LT and T 2 . The key issues for orbit drift are 1) accounting for the diurnal cycle and 2) the adjustment needed to correct for spurious effects related to the temperature of the instrument. In addition, new calibration coefficients for NOAA-12 have been applied. The net global effect of these revisions (version D) is small, having little impact on the year-to-year anomalies. The change in global trends from C to D for 1979-98 for T 2LT is an increase from 0.03 to 0.06 K decade 1 , and a decrease for T 2 from 0.08 to 0.04 K decade 1 .