Abstract
We have performed an analysis of reprocessed GPS/MET data spanning 1995–1997 generated by CDAAC in 2007. CDAAC developed modified dual-frequency processing methods for the encrypted data (AS-on) during 1995–1997. We compared the CDAAC data set to the MERRA-2 reanalysis, separately for AS-on and AS-off, focusing on the altitude range 10–30 km. MERRA-2 did not assimilate GPS/MET data in the period 1995–1997. To gain insight into the CDAAC data set, we developed a single-frequency data set for GPS/MET, which is unaffected by the presence of encryption. We find excellent agreement between the more limited single frequency data set and the CDAAC data set: the bias between these two data sets is consistently less than 0.25 % in refractivity, whether or not AS is on. Given the different techniques applied between the CDAAC and JPL data sets, agreement suggests that the CDAAC AS-on processing and the single frequency processing are not biased in an aggregate sense greater than 0.25 % in refractivity, which corresponds approximately to a temperature bias less than 0.5 K. Since the profiles contained in the new single frequency data set are not a subset of the CDAAC profiles, the combination of the CDAAC data set, consisting of 9,579 profiles, and the new single-frequency data set, consisting of 4,729 profiles, yields a total number of 11,531 unique profiles from combining the JPL and CDAAC data sets. All numbers are after quality control has been applied by the respective processing activities.
Highlights
There is currently intense interest in Earth science observations that are useful for measuring decadal scale changes to the 35 climate (Wielicki et al, 2013)
We compared the COSMIC Data Analysis and Archive Center (CDAAC) data set to the MERRA-2 reanalysis, separately for AS-on and AS-off, focusing on the altitude range 10-30 km
To gain insight into the CDAAC data set, we developed a single-frequency data set for GPS/MET, which is unaffected by the presence of encryption
Summary
There is currently intense interest in Earth science observations that are useful for measuring decadal scale changes to the 35 climate (Wielicki et al, 2013) When considering such observations from orbiting platforms, measurement accuracy needs to be characterized over time scales that exceed the lifetime of any single mission (Gleisner et al, 2020). A significant challenge in observing decadal-scale climate change is that geophysical variables display significant variation on time scales shorter 45 than tens of years. Such “natural variability” is potentially the most significant factor hindering the interpretation of observations relevant to climate change (Leroy et al, 2008; Santer et al, 2017). It is widely recognized that the longer a time series is, the more valuable it is for observing climate change (Leroy et al, 2008; Wielicki et al, 2013)
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