Important New Paper ” Using Limited Time Period Trends as a Means to Determine Attribution of Discrepancies in Microwave Sounding Unit Derived Tropospheric Temperature Time” By R. M. Randall and B. M. Herman

There has been considerable discussion on the use of microwave sounding unit (MSU) data to assess multi-decadal tropspheric temperature trends (e.g. see CCSP, 2006). An important new paper is in press in the Journal of Geophysical Research which adds new insight into this issue including a comparison of the analyses from two of the leading groups that analyze multi-decadal tropospheric temperature trends from the MSU data [i.e. University of Alabama at Huntsville (UAH) and Remote Sensing Systems (RSS)]

The paper is

Randall, R. M., and B. M. Herman (2007), Using Limited Time Period Trends as a Means to Determine Attribution of Discrepancies in Microwave Sounding Unit Derived Tropospheric Temperature Time Series, J. Geophys. Res., doi:10.1029/2007JD008864, in press

with the abstract

“Limited Time Period (LTP) running trends are created from various Microwave Sounding Unit (MSU) difference time series between the University of Alabama in Huntsville (UAH) and Remote Sensing System (RSS) group’s lower troposphere (LT) and mid troposphere to lower stratosphere (MT) channels. This is accomplished in an effort to determine the causes of the greatest discrepancies between the two data sets.Results indicate the greatest discrepancies were over time periods where NOAA-11 through NOAA-15 adjustments were applied to the raw LT data over land. Discrepancies in the LT channel are shown to be dominated by differences in diurnal correction methods due to orbital drift; however, discrepancies from target parameter differences are also present.Comparison of MSU data with the a reduce RATPAC radiosonde dataset indicates that RSS’s method (use of climate model) of determining diurnal effects is likely 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. Our findings enhance the importance of understanding temporal changes in the atmospheric temperature trend profile and their implications on current climate studies.”

One of the important results of this study is that

“Figure 5 shows that 10-year trends center on the mid-1994’s through 10 year trends centered on the mid-1995’s indicates the RSS−Sonde trends are significantly different from zero where the Sonde−UAH trends are not. In addition, for 10-year trends centered on late-1999 through 10- years trend centered on early 2000 the RSS−Sonde trends are significantly different from zero where Sonde−UAH are marginally not. Another key feature in the RSS−Sonde series is the rapid departure in trend magnitude from trends centered on 1995 through trends centered on late-1999 where the Sonde−UAH magnitude in trends is nearly constant. These features are consistent with the diurnal correction signatures previously discussed. These findings the RSS method for creating the diurnal correction (use of a climate model) is cause for discrepancies between RSS and UAH databases in the LT channel.”

“We compared the MSU data to the radiosonde data and found that the RSS−Sonde is significantly different from zero while Sonde−UAH is not during time periods that are consistent with overcorrected diurnal corrections dominating the LT channel. We used “good��? radiosonde data [Randel and Wu, 2006] in order to minimize negative trend biases in stratospheric and upper tropospheric radiosonde data. Corrected diurnal signatures were shown to still exist in the RSS LT time series. The longer 10-year LTP trends were additionally shown to have a positive bias, thus the present corrected diurnal signatures are likely affecting the long term trend with a warm bias. RSS’s method is likely overestimating the diurnal correction in the LT channel, it follows that the same process is invoking a discrepancy in the diurnal correction in the MT channel. An initial overestimation of the diurnal correction may be small enough to either be masked or dominated by the target factors in the MT channel, but further research is necessary to isolate which correction method is dominant, if any.”

While both UAH and RSS are outstanding research groups, with respect to the assessment of multi-decadal tropospheric temperature trends, the independent comparison reported in Randall and Herman indicates that the trend values of the UAH group are more accurate.

Comments Off on Important New Paper ” Using Limited Time Period Trends as a Means to Determine Attribution of Discrepancies in Microwave Sounding Unit Derived Tropospheric Temperature Time” By R. M. Randall and B. M. Herman

Filed under Climate Change Metrics

Comments are closed.