Using Limited Time Periods as a Means to Evaluate Microwave Sounding Unit Derived Tropospheric Temperature Trend Methods

Abstract

Limited Time Period (LTP) running trends are used to evaluate Microwave Sounding Unit (MSU) derived tropospheric temperature trend methods in an attempt to alleviate documented considerable disagreements between tropospheric datasets so investigation into the atmospheric variability is able to move forward.Regression derived coefficients were used to combine lower stratosphere (LS) and mid-troposphere to lower stratosphere (MT) simulated MSU channels from RATPAC radiosonde data. This protocol is used to estimate tropospheric temperature trends and compared to actual RATPAC derived tropospheric temperature trends. It is found that the statistical LS/MT combination results in greater than 50% error over some LTP. These errors are found to exist when strong cooling in the stratosphere is coincident with periods when the level separating cooling from warming is above the tropopause.LTP trends are also created from various MSU difference time series between the University of Alabama in Huntsville (UAH) and Remote Sensing System (RSS) group's lower troposphere (LT) and MT channels. Results suggest the greatest discrepancies over time periods where NOAA-11 through NOAA-15 adjustments was applied to the raw LT data over land. Discrepancies are shown to be dominated by differences in diurnal correction methods due to orbital drift. Comparison of MSU data with radiosonde data indicate that RSS's method of determining diurnal effects is overestimating the correction in the LT channel. Diurnal correction signatures still exist in the RSS LT time series and are likely affecting the long term trend with a warm bias.These findings suggest atmospheric amplification is not happening in the atmosphere using globally averaged data over the MSU era. There is evidence however from the radiosonde data that shows greater warming in the ~300-500 hPa layer than at the surface during some LTP in the complete radiosonde database. This temporal change in temperature trends warrants further studies on this subject.This research suggests overall that the temporal changes in temperature trend profiles and their causes are extremely important in our understanding of atmospheric changes and are themselves, not well characterized.