CoAuthors

R. Steven Nerem (University of Colorado, United States); Gary Mitchum (USF College of Marine Science, United States)

The 24-year global mean sea level (GMSL) climate record made possible by the TOPEX and Jason-series of altimeter missions is an important indicator of climate change. It is being increasingly relied upon for determining evidence of changing rates in the climate system. Therefore, understanding the variability within the GMSL time series is important. Decomposing the record into a long-term and seasonal components leaves a signal with variability on different time scales, from seemingly random short fluctuations to interannual and possible decadal periods. The degradation of the point target response (PTR) on the TOPEX A altimeter and the subsequent switch to the redundant TOPEX B altimeter can be viewed as a new “mission,” albeit on the same spacecraft platform. But unlike the inter-mission phases between TOPEX/Poseidon and Jason-1 or Jason-1 and Jason-2 that allowed intercomparison and bias estimation to link the GMSL climate data record, the change in altimeters at the TOPEX A to B transition did not allow the two altimeters to be intercompared. This represents a potential discontinuity in the GMSL time series that have implications for estimating trends and accelerations and interpreting the climate record. Following renewed efforts to retrack and improve the TOPEX A and B altimeter records by Callahan [2016] and an investigation by Beckley et al. [2016] into the effect of “Cal-1” correction applied to TOPEX MGDR-B, we have reanalyzed our CU GMSL time series taking into account the results of Beckley et al. In this work, we give an update on the CU GMSL time series with the addition of Jason-3 and updated corrections, a recent comparison between all of the altimeters and the tide gauge network, and also summarize our initial efforts to improve the overall TOPEX record and better reconcile the transition from the TOPEX A to TOPEX B altimeter.

References
Beckley, B., Ray, R., Mitchum, G., & Hancock, D. (2016). On the “cal mode” correction to TOPEX altimetry and its effect on the global mean sea-level time series. Presented at the OSTST 2016, La Rochelle, France.

Callahan, P. (2016). Retracked TOPEX Climate Data Record. Presented at the OSTST 2016, La Rochelle, France.