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Using A-Train Polar Stratospheric Cloud Information to Validate Polar Stratospheric Reanalysis Temperatures

Stratospheric polar processes, such as the potential for ozone loss via heterogeneous chemical reactions, depend critically on temperature. We have assessed the temperature biases of several modern meteorological reanalysis datasets.

Six years of unprecedented near simultaneous A-Train measurements by CALIPSO / CALIOP and Aura MLS were used to classify polar stratospheric cloud (PSC) types and determine the ambient water vapor and nitric acid. This information enabled the calculation of two independent reference atmospheric temperature datasets from the theoretical thermodynamic equilibrium existence conditions of PSCs composed of liquid supercooled ternary solutions (L) and water ice (I). Biases in reanalysis temperature datasets produced by several meteorological data centers were estimated by comparisons to the PSC reference temperatures and to COSMIC GPS temperatures (C).

Polar temperatures from modern meteorological reanalyses are in much better agreement than were their counterparts from previous decades. Increased confidence in the accuracy of polar reanalysis temperatures provides tighter constraints on model parameterizations of microphysics/chemistry used to represent polar chemical processing.

summary of the mean temperature bias ranges
Temperature bias ranges of the reanalyses relative to the polar stratospheric liquid cloud (L) and ice cloud (I) temperature references, calculated from equilibrium thermodynamics (see text opposite), and COSMIC GPS (C) temperatures, for Antarctic and Arctic winters 2008- 2013, poleward of 60°, and for pressures 68 hPa to 21 hPa.

Technical Description of Figure:
The figure shows a summary of the mean temperature bias ranges of the reanalyses relative to the liquid (L: -1.6 to -0.3 K) and ice (I: -0.9 to +0.1 K) equilibrium references and COSMIC GPS (C: -0.5 to +0.2 K) in the Antarctic and Arctic.

Scientific significance, societal relevance, and relationships to future missions:
Stratospheric ozone depletion has been a central theme of atmospheric science since the discovery of the Antarctic ozone hole. Formation of polar stratospheric cloud particles and the heterogeneous chemistry which takes place on their surfaces are threshold processes that depend critically on temperature. Temperature biases in older meteorological reanalyses often rendered them unsuitable for accurate modeling of the interannual variability of PSC formation, and the subsequent denitrification, chlorine activation and chemical ozone loss. We have shown that the temperatures from modern meteorological reanalyses are in much better agreement, and therefore provide tighter constraints on the extent to which any resulting deficiencies in modeled chlorine activation and/or modeled ozone losses can be ascribed to temperature biases. This research was carried out as part of the SPARC Reanalysis Intercomparison Project (S-RIP).

Data Sources:
MLS/Aura Level 2 Temperature V004, MLS Science Team,
MLS/Aura Level 2 Nitric Acid (HNO3) Mixing Ratio V004, MLS Science Team,
MLS/Aura Level 2 Water Vapor (H2O) Mixing Ratio V004, MLS Science Team,
MERRA inst6_3d_ana_Nv: 3D Analyzed State, Meteorology Instantaneous 6-hourly V5.2.0, Global Modeling and Assimilation Office (GMAO),
MERRA-2 inst3_3d_asm_Nv: 3d, 3-Hourly, Instantaneous, Model-Level, Assimilation, Assimilated Meteorological Fields V5.12.4, Global Modeling and Assimilation Office (GMAO),
NCEP Climate Forecast System Reanalysis (CFSR) 6-hourly Products, National Centers for Environmental Prediction
ERA-Interim Project, European Centre for Medium-Range Weather Forecasts,
Japanese 55-year Reanalysis, Daily 3-Hourly and 6-Hourly Data, Japan Meteorological Agency ,
CALIPSO/CALIOP Level 1B, Lidar Profile Data, versions 3.01, 3.02 and 3.30, CALIPSO Science Team
CALIPSO/CALIOP Level 2, Polar Stratospheric Cloud Data, version 1.00, CALIPSO Science Team,

References: Lambert, A. and Santee, M. L.: Accuracy and precision of polar lower stratospheric temperatures from reanalyses evaluated from A-Train CALIOP and MLS, COSMIC GPS RO, and the equilibrium thermodynamics of supercooled ternary solutions and ice clouds, Atmos. Chem. Phys., 18, 1945-1975,, 2018.