79-- Early online release-- Chapter 3 : Overview of Temperature and Winds

Two of the most basic parameters generated from a reanalysis are temperature and winds. Temperatures in the reanalyses are derived from conventional (surface and balloon), aircraft, and satellite observations. Winds are observed by conventional systems, cloud tracked, and derived from height fields, which are in turn derived from the vertical temperature structure. In this chapter we evaluate as part of the SPARC Reanalysis Intercomparison Project (S-RIP) the temperature and wind structure of all the recent and past reanalyses. This evaluation is mainly among the reanalyses themselves, but comparisons against independent observations, such as HIRDLS, MLS, COSMIC, ozonesonde, and rocketsonde temperatures are also presented. This evaluation uses monthly mean and 2.5° zonal mean data sets and spans the satellite era from 1979 – 2014. There is very good agreement in temperature seasonally and latitudinally among the more recent reanalyses (CFSR/CFSv2, MERRA, ERA-Interim, JRA-55, and MERRA-2) between the surface and 10 hPa. At lower pressures there is increased variance among these reanalyses that changes with season and latitude. This variance also changes during the time span of these reanalyses with greater variance during the TOVS period (1979 – 1998) and less variance afterward in the ATOVS period (1999 – 2014). There is a distinct change in the temperature structure in the middle and upper stratosphere during this transition from TOVS to ATOVS systems. Consult Chapter 2 Section 2.4. 3.2 (Observational Data/Satellite Data) for more information about the TOVS and ATOVS suite of instruments and usage by the various reanalyses. Zonal winds for the entire period have lower variance among the reanalyses than the temperatures and this lower variance extends to lower pressures than the temperatures. The temperatures and winds throughout the stratosphere in the older reanayses (NCEP-NCAR R1, NCEP-DOE R2, ERA-40, and JRA-25) show significant differences from a Reanalysis Ensemble Mean for the same time periods than in the more recent reanalyses, both during the TOVS and ATOVS periods. The transition of temperatures from the TOVS to ATOVS periods continues to be an issue even for the more recent reanalyses. All reanalyses to date have issues analysing the quasi-biennial oscillation (QBO) winds. Comparisons with Singapore QBO winds show disagreement in the amplitude of the westerly and easterly anomalies. The disagreement with Singapore winds improves with the transition from TOVS to ATOVS observations. Aura HIRDLS and Aura MLS temperatures have similar bias characteristics when compared with a reanalysis ensemble mean (MERRA, ERA-Interim, and JRA-55). There is good agreement among the NOAA TLS, SSU1, and SSU2 Climate Data Records and layer mean temperatures from the more recent reanalyses. Caution is advised when using reanalysis temperatures for trend detection and anomalies from a long climatology period as the quality and character of reanalyses have changed over time. Sean Davis Chemical Sciences Laboratory, National Oceanic and Atmospheric Administration USA Daniel Mitchell University of Bristol United Kingdom Corwin Wright University of Bath United Kingdom Craig Long National Oceanic and Atmospheric Administration