Assessment of upper tropospheric and stratospheric water vapor and ozone in reanalyses as part of S-RIP

Abstract

Abstract. Reanalysis data sets are widely used to understand atmospheric processes and past variability, and are often used to stand in as "observations" for comparisons with climate model output. Because of the central role of water vapor (WV) and ozone (O 3 ) in climate change, it is important to understand how accurately and consistently these species are represented in existing global reanalyses. In this paper, we present the results of WV and O 3 intercomparisons that have been performed as part of the SPARC (Stratospheretroposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The comparisons cover a range of timescales and evaluate both inter-reanalysis and observation-reanalysis differences. We also provide a systematic documentation of the treatment of WV and O 3 in current reanalyses to aid future research and guide the interpretation of differences amongst reanalysis fields.The assimilation of total column ozone (TCO) observations in newer reanalyses results in realistic representations of TCO in reanalyses except when data coverage is lacking, such as during polar night. The vertical distribution of ozone is also relatively well represented in the stratosphere in reanalyses, particularly given the relatively weak constraints on ozone vertical structure provided by most assimilated observations and the simplistic representations of ozone photochemical processes in most of the reanalysis forecast models. However, significant biases in the vertical distribution of ozone are found in the upper troposphere and lower stratosphere in all reanalyses.Published by Copernicus Publications on behalf of the European Geosciences Union. S. M. Davis et al.: Reanalysis UTLS water vapor and ozone assessmentIn contrast to O 3 , reanalysis estimates of stratospheric WV are not directly constrained by assimilated data. Observations of atmospheric humidity are typically used only in the troposphere, below a specified vertical level at or near the tropopause. The fidelity of reanalysis stratospheric WV products is therefore mainly dependent on the reanalyses' representation of the physical drivers that influence stratospheric WV, such as temperatures in the tropical tropopause layer, methane oxidation, and the stratospheric overturning circulation. The lack of assimilated observations and known deficiencies in the representation of stratospheric transport in reanalyses result in much poorer agreement amongst observational and reanalysis estimates of stratospheric WV. Hence, stratospheric WV products from the current generation of reanalyses should generally not be used in scientific studies.

An intercomparison of tropospheric ozone reanalysis products from CAMS, CAMS interim, TCR-1, and TCR-2

“…It is coupled to the atmospheric general circulation model MIROC-AGCM version 4 (Watanabe et al, 2011). The simulated meteorological fields were nudged toward the 6-hourly ERA-Interim (Dee et al, 2011) to reproduce past meteorological fields.…”

Recent Decline in Extratropical Lower Stratospheric Ozone Attributed to Circulation Changes

“…The MERRA-2 ozone products are described and evaluated in Wargan et al (2017), McCarty et al (2016), and Davis et al (2017). MERRA-2 assimilates partial column ozone from a series of SBUV instruments between 1980 and September 2004.…”

Toward a Reanalysis of Stratospheric Ozone for Trend Studies: Assimilation of the Aura Microwave Limb Sounder and Ozone Mapping and Profiler Suite Limb Profiler Data

“…These results highlight the ability of limb ozone assimilation to represent the ozone responses to the QBO correctly, as previously demonstrated for MLS (Coy et al, ). This is in contrast to a number of reanalyses that assimilate layer ozone from nadir Solar Backscatter UltraViolet radiometers (SBUV) but not limb observations, for example, MERRA‐2 prior to 2004: due to large vertical smoothing errors inherent in ozone data derived from nadir observations (Kramarova et al, ) the downward phase propagation of the ozone QBO signal in these reanalyses is often poorly represented (Davis et al, , their Figure ; Coy et al, ).…”