Total Ozone Analysis Using OMPS and CrIS

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This algorithm is a new generation of the current operational TOAST. It replaces data from the sensors, used to compose the TOAST (SBUV/2 and HIRS) with the most newly developed sensors: OMPS NP and CrIS. This leads to improve the product accuracy and provide continuity of TOAST contributions to the ozone researchers and other users.

This new algorithm has been developed as the legacy of the TOAST. Instead of estimating the UTLS ozone by HIRS provided total amount retrieval, a full troposphere and lower stratosphere (FTLS) ozone has been accurately derived based on the fine height resolution profile retrieved from CrIS hyper-spectral observation. The mid-to-upper stratosphere (MSUS) ozone has been analyzed using the new generation ozone profiler OMPS NP to replace the SBUV/2.

Following information has been provided by Jianguo Niu (STAR): OMPS NP, like the heritage SBUV/2 instruments, is a nadir-viewing double grating optical instrument. But instead of scanning through wavelengths with a single photomultiplier as its detector, OMPS employs a CCD detector at the grating focal plan to record full spectrum. Its wavelength range covers from 250 to 310 nm every 0.42 nm with 1.1 nm FWHM spectral resolution [Dittman, 2002]. The NOAA version-6 Interface Data Processing system (IDPS) algorithm [Bhartia et al., 2996] is used in OMPS NP retrieval. A set of 12 wavelengths (at approximately 252, 274, 283, 288, 292, 298, 302, 306, 313, 318, 331 and 340 nm) are used to estimate the ozone amounts in 12 Umkehr layers and the total column ozone. The 313, 318, 331, and 340 nm channel measurements are obtained from the OMPS Nadir Mapper (OMPS NM) [Flynn 2013]. The pressures at the lower boundaries of the 12 Umkehr layers are at: [1013, 253, 127, 63.3, 31.7, 15.8, 7.93, 3.96, 1.98, 0.99, 0.50, 0.25] hPa. The OMPS NP provides the approximately 14 orbits/day of observations (i.e. 1100 granules/day), but with its nadir-only viewing characteristics, it provides profile retrievals for 12 Umkehr layers (or 21-layer for the Version-8 algorithm) along the orbital track without a cross-track dimension to the observations.

The CrIS instrument on S-NPP [Han, Y. 2013] is a major step forward in the U.S. operational IR sounding capability previously provided by the HIRS instruments of the TIROS-N TOVS series. CrIS obtains good daily spatial coverage by using a cross-track scan mirror to cover a 2200-km wide swath with 30 earth-scene fields-of-regard (FOR). Each FOR consists of 9 fields-of-views (FOVs), aggregated into a 3x3 array of 14 km diameter spots in the nadir. CrIS is a plane mirror Michelson interferometer Fourier transform spectrometer, providing a spectral resolution of 0.625 cm-1 at the long-wave IR (LWIR) band from 650 to 1095 cm-1 which includes the ozone absorption band around 1040 cm-1. One CrIS EDR granule contains four cross-track swaths of 120 observations (i.e. 2700 granules/day); the same orbits per day number as OMPS NP provides full global coverage. Unlike the HIRS retrieval product used in the current TOAST, CrIS retrieves not only ozone total amount but also a 100-layer ozone profile. This significant instrument improvement provides us more accurate ozone information within UTLS than that former TOAST HIRS provides.

The basic consideration of TOAST products is to utilize the properties of IR measurements’ sensitivity to the ozone distribution in the lower atmosphere, and of UV measurements’ sensitivity to the ozone distribution in the upper atmosphere. The total amounts of ozone are a combination of the FTLS ozone and the MSUS ozone retrieved from CrIS IR observations, and from OMPS NP UV observations, respectively.

To combine the two sensors, the profile pressure scale of CrIS need to be converted into the OMPS NP scale, then a series of coordinate transformation need to be conducted from geographic into stereographic coordinate before carrying out the objective analysis. The objective analysis in this study is to improve an initially assumed global ozone distribution (the first guess) by incorporating the currently available satellite measurements. At last, this analyzed global ozone data are transformed back to the original geographic coordinate with resolution of 1 by 1 degree.

The Ozone team continually monitors the performance of the various SBUV/2, OMPS and CrIS instruments and will vary the combination used in the distributed TOAST product to provide the best quality product.