A Global Ozone Profile Climatology for Satellite Retrieval 1 Algorithms Based on Aura MLS Measurements and the 2 MERRA-2 GMI Simulation 3

. A new atmospheric ozone profile climatology has been constructed by combining 13 daytime ozone profiles from the Aura Microwave Limb Sounder (MLS) and Modern‐Era 14 Retrospective Analysis for Research Applications version 2 (MERRA2) Global Modeling 15 Initiative (GMI) model simulation (M2GMI). The MLS and M2GMI ozone profiles are merged 16 between 13 and 17 km (~159 and 88 hPa) with MLS used for stratospheric and GMI for 17 primarily tropospheric levels. The time record for profiles from MLS and GMI is August 2004- 18 December 2016. The derived seasonal climatology consists of monthly zonal-mean ozone 19 profiles in 5-degree latitude bands from 90 o S-90 o N covering altitudes (in Z* log-pressure 20 altitude) from zero to 80 km in 1 km increments. This climatology can be used as a priori 21 information in satellite ozone retrievals, in atmospheric radiative transfer studies, and as a 22 baseline to compare with other measured or model-simulated ozone. The MLS/GMI seasonal 23 climatology shows a number of improvements compared to previous ozone profile climatologies 24 based on MLS and ozonesonde measurements. These improvements are attributed mostly to 25 continuous daily global coverage of GMI tropospheric ozone compared to sparse regional 26 measurements from sondes. Only daytime measurements for MLS are used in the MLS/GMI 27 climatology compared to the previous MLS/sonde climatology that averaged MLS day and night 28 measurements together; the daytime-only measurements are important for applications involving the upper stratosphere and lower mesosphere where the ozone diurnal cycle is large. In addition 30 to the seasonal climatology, we also derive an additive climatology to account for inter-annual 31 variability in stratospheric zonal-mean ozone profiles which is based on a rotated empirical 32 orthogonal function (REOF) analysis of Aura MLS ozone profiles. This REOF climatology 33 starts in 1970 and captures most of the inter-annual variability in global stratospheric ozone 34 including Quasi-Biennial Oscillation (QBO) signatures.

The application of the MLS/GMI seasonal climatology by itself or together with the REOF inter-67 annual climatology as a priori enables more accurate profile and column ozone retrievals,  In the following sections we describe the data and GMI model output used in our analysis, 80 outline the methods used to construct the MLS/GMI seasonal climatology and REOF 81 climatology, and discuss the properties of the climatologies. We conclude with a summary of    four follow-up OMPS instrumental suites as a part of JPSS program (with JPSS-1/NOAA-20 126 already in operation) that will extend the SBUV-type ozone observations in the next two 127 decades. The SBUV instruments retrieve broad ozone profiles from measurements of 128 backscattered solar UV radiation which can be integrated to give total column ozone. All MOD 129 instrument measurements have been processed using the v8.6 retrieval algorithm as described by    Fig. 1). The largest differences were in the tropics where M2GMI was lower than sonde by up to 179 10-20% in low-mid troposphere, but in the tropical tropopause region M2GMI was higher than 180 sonde by 40-50%; the large percentage differences however can be due to relatively low mean    The MLS/GMI seasonal climatology product is derived for both volume mixing ratio (units 222 ppmv) and vertical column concentration (DU km -1 ); the latter has vertical and latitudinal 223 structure that is closely similar to that of ozone number density and ozone partial pressure. error covariance matrices included as a priori information in retrieval algorithms such as the 228 optimal estimation method of Rodgers (2000). We refer the reader to the Supplementary 229 Materials for further discussion and figures involving calculated standard deviations. Our motivation for using M2GMI simulation is that they provide better spatial and temporal        Figure 4 shows the difference between ML and MLS/GMI zonal-mean profile ozone by season, 317 plotted as Z* altitude versus latitude. Only Z * levels 0-30 km are included in Fig. 4 to highlight 318 differences in ozone profiles used for the troposphere and the low stratosphere merging region.

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Year-round positive differences in the tropics in Fig. 4 suggest that ML is always too large in the 320 13 low-mid troposphere compared to M2GMI due to absence of ML sonde measurements in the 321 Pacific region where tropospheric ozone is low (e.g., Fig. 2). At latitudes around ±35 o and 322 elsewhere in the low stratosphere merging region in Fig. 4 there are anomalous differences from 323 −0.5 up to +1.5 DU km -1 ; these sharp patterns are ascribed to sonde sampling issues for the ML 324 climatology. In the boundary layer throughout the NH extra-tropics during winter (i.e., upper 325 left panel in Fig. 4) the M2GMI ozone is higher than sondes by ~0.5 to 1 DU km -1 . These latter   Fig. 5 for 0-8 km (Fig. 5a) and 0-16 km (Fig. 5b). These line plots are determined from     The main challenge of EOF analysis is interpretation of derived EOFs and EOF time coefficients 387 and their attribution to specific geophysical processes. As described in the Supplementary 388 Materials, the construction of this REOF climatology required only total ozone and tropical 389 stratospheric zonal wind time series to explain most of stratospheric ozone profiles variability 390 (total EOF variance). We used MLS ozone anomalies expressed as ozone partial pressure for the 391 REOF analysis rather than ozone mixing ratio because it helped to attribute the REOF-1 time 392 coefficient directly to total ozone column measurements at all latitudes. The first REOF vector 393 with the MOD total ozone time series as a proxy explains about 50-70% of the inter-annual 394 ozone variability. Next, we derived a second REOF-2 that we attributed to the QBO and used  Aura time period whenever total column ozone and wind data are available.

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The REOF climatology was finally converted from the ozone partial pressures defined at 30 403 MLS levels to volume mixing ratio (ppmv) and partial ozone column (DU km -1 ) at the 1 km Z * 404 levels (defined in section 3.2) identical to the MLS/GMI climatology. The REOF climatological 405 values at levels below ~9 km and above ~48 km are very small in contributing to inter-annual 406 variability of ozone and are set to zero. Since the REOF climatology uses zonal wind and total 407 ozone time series that can have long-term trends, we applied a very low frequency (VLF) digital 408 low-pass filter to the final derived REOF climatology to remove long-term decadal variability.

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This was done to ensure that the climatology captures only inter-annual variability in monthly 410 zonal mean ozone anomaly profiles without inducing decadal trends if used as a prior in ozone 411 retrieval. The frequency response of the applied VLF digital filter (Stanford and Ziemke, 1993) 412 is exactly 0.0 (1.0) at zero (Nyquist) frequency with an amplitude of 0.5 at frequency 0.00333 413 month -1 ; the filter was also designed to have zero phase shift at all frequencies.  The long record of the REOF inter-annual ozone profile climatology has been compared with de-441 seasonalized ozone profile measurements from SAGE II and Aura MLS for 1984-2018 (Fig. 7).

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The top panel in Fig. 7a       University of Berlin from https://www.geo.fu-berlin.de/met/ag/strat/produkte/qbo/qbo.dat. The 524 seasonal and inter-annual climatology products derived from our study are available for the 525 general public using direct links from the NASA webpage https://avdc.gsfc.nasa.gov/.