Satellite data validation: a parametrization of the natural variability of atmospheric mixing ratios

High-resolution model data are used to estimate the statistically typical mixing ratio variabilities of trace species as a function of distance and time separation. These estimates can be used to explain the fact that some of the differences between observations made with different observing systems are due to the less-than-perfect co-location of the measurements. The variability function is approximated by a two-parameter regression function, and lookup tables of the natural variability values as a function of distance separation and time separation are provided. In addition, a reparametrization of the variability values as a function of latitudinal gradients is proposed, and the seasonal independence of the linear approximation of such a function is demonstrated

Tropospheric ozone retrieval by a combination of TROPOMI/S5P measurements with BASCOE assimilated data

We present a new tropospheric ozone dataset based on TROPOspheric Monitoring Instrument (TROPOMI)/Sentinel-5 Precursor (S5P) total ozone measurements combined with stratospheric ozone data from the Belgian Assimilation System for Chemical ObsErvations (BASCOE) constrained by assimilating ozone observations from the Microwave Limb Sounder (MLS). The BASCOE stratospheric data are interpolated to the S5P observations and subtracted from the TROPOMI total ozone data. The difference is equal to the tropospheric ozone residual column from the surface up to the tropopause. The tropospheric ozone columns are retrieved at the full spatial resolution of the TROPOMI sensor (5.5×3.5 km2) with daily global coverage. Compared to the Ozone Mapping and Profiler Suite Modern-Era Retrospective analysis for Research and Applications 2 (OMPS-MERRA-2) data, a global mean positive bias of 3.3 DU is found for the analysed period April 2018 to June 2020. A small negative bias of about −0.91 DU is observed in the tropics relative to the operational TROPOMI tropical tropospheric data based on the convective cloud differential (CCD) algorithm throughout the same period. The new tropospheric ozone data (S5P-BASCOE) are compared to a set of globally distributed ozonesonde data integrated up to the tropopause level. We found 2254 comparisons with cloud-free TROPOMI observations within 25 km of the stations. In the global mean, S5P-BASCOE deviates by 2.6 DU from the integrated ozonesondes. Depending on the latitude the S5P-BASCOE deviate from the sondes and between −4.8 and 7.9 DU, indicating a good agreement. However, some exceptional larger positive deviations up to 12 DU are found, especially in the northern polar regions (north of 70∘). The monthly mean tropospheric column and time series for selected areas showed the expected spatial and temporal pattern, such as the wave one structure in the tropics or the seasonal cycle, including a summer maximum, in the mid-latitudes.</p

Evaluation of the N2_2O Rate of Change to Understand the Stratospheric Brewer‐Dobson Circulation in a Chemistry‐Climate Model

The Brewer-Dobson Circulation (BDC) determines the distribution of long-lived tracers in the stratosphere; therefore, their changes can be used to diagnose changes in the BDC. We evaluate decadal (2005–2018) trends of nitrous oxide (N$_2$O) in two versions of the Whole Atmosphere Chemistry-Climate Model (WACCM) by comparing them with measurements from four Fourier transform infrared (FTIR) ground-based instruments, the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), and with a chemistry-transport model (CTM) driven by four different reanalyses. The limited sensitivity of the FTIR instruments can hide negative N$_2$O trends in the mid-stratosphere because of the large increase in the lowermost stratosphere. When applying ACE-FTS measurement sampling on model datasets, the reanalyses from the European Center for Medium Range Weather Forecast (ECMWF) compare best with ACE-FTS, but the N$_2$O trends are consistently exaggerated. The N$_2$O trends obtained with WACCM disagree with those obtained from ACE-FTS, but the new WACCM version performs better than the previous above the Southern Hemisphere in the stratosphere. Model sensitivity tests show that the decadal N$_2$O trends reflect changes in the stratospheric transport. We further investigate the N$_2$O Transformed Eulerian Mean (TEM) budget in WACCM and in the CTM simulation driven by the latest ECMWF reanalysis. The TEM analysis shows that enhanced advection affects the stratospheric N$_2$O trends in the Tropics. While no ideal observational dataset currently exists, this model study of N$_2$O trends still provides new insights about the BDC and its changes because of the contribution from relevant sensitivity tests and the TEM analysis

Tropospheric ozone column data records based on total columns from GOME, SCIAMACHY, GOME-2, OMI and TROPOMI using CCD algorithm or in combination with BASCOE/MLS

A long-term tropospheric ozone time series has been generated for the tropical band (20°S to 20°N) based on convective cloud differential algorithm (CCD). Tropical tropospheric ozone columns were retrieved from several European sensors starting with observations by GOME in 1995 and including data from SCIAMACHY, OMI, GOME-2A and GOME-2B. It has now been extended by DLR with data from GOME-2C and TROPOMI and now encompasses 25 years. The tropospheric ozone retrieval for all data sets is based on the total columns retrieved with the GODFIT algorithm and associated cloud products. There are however some differences between the different tropospheric columns from the different sensors which have to be corrected for. For the CCD time series, we used SCIAMACHY data as reference and fitted an offset and a trend correction to the data of the other sensors. We estimated the trend based on the long-term time series. For the tropics an overall trend of +0.7 DU/decade was found in the data set until 2019, varying locally between -0.5 and 1.8 DU/decade. The second data record combines total ozone columns from TROPOMI with BASCOE stratospheric ozone profiles. BASCOE stratospheric ozone data is constrained by assimilated Aura MLS observation and it is provided with 3-hour time resolutions in NRT. We used the BASCOE NRT data set to calculate the stratospheric ozone columns for every day from April 2018 to December 2020 and subtracted it from the respective NRT total columns observed by TROPOMI. The TROPOMI NRT total ozone product was updated recently including a new surface albedo retrieval algorithm. An internal reanalysis of the NRT data was used to create a consistent tropospheric ozone data set. A comparison to ozone sondes showed a good agreement for most part of the world. For the GEMS validation the TROPOMI total ozone NRT algorithm is applied to selected the GEMS data. Also, the tropospheric ozone column might be retrieved based on the TROPOMI-BASCOE algorithm described above. Both the CCD and the TROPOMI-BASCOE tropospheric ozone data will be presented. Furthermore, first results for total and troposheric ozone columns of GEMS data using the TROPOMI algorithms might be shown

Evaluation of the N2O Rate of Change to Understand the Stratospheric Brewer‐Dobson Circulation in a Chemistry‐Climate Model

peer reviewedThe Brewer-Dobson Circulation (BDC) determines the distribution of long-lived tracers in the stratosphere; therefore, their changes can be used to diagnose changes in the BDC. We evaluate decadal (2005–2018) trends of nitrous oxide (N2O) in two versions of the Whole Atmosphere Chemistry-Climate Model (WACCM) by comparing them with measurements from four Fourier transform infrared (FTIR) ground-based instruments, the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS), and with a chemistry-transport model (CTM) driven by four different reanalyses. The limited sensitivity of the FTIR instruments can hide negative N2O trends in the mid-stratosphere because of the large increase in the lowermost stratosphere. When applying ACE-FTS measurement sampling on model datasets, the reanalyses from the European Center for Medium Range Weather Forecast (ECMWF) compare best with ACE-FTS, but the N2O trends are consistently exaggerated. The N2O trends obtained with WACCM disagree with those obtained from ACE-FTS, but the new WACCM version performs better than the previous above the Southern Hemisphere in the stratosphere. Model sensitivity tests show that the decadal N2O trends reflect changes in the stratospheric transport. We further investigate the N2O Transformed Eulerian Mean (TEM) budget in WACCM and in the CTM simulation driven by the latest ECMWF reanalysis. The TEM analysis shows that enhanced advection affects the stratospheric N2O trends in the Tropics. While no ideal observational dataset currently exists, this model study of N2O trends still provides new insights about the BDC and its changes because of the contribution from relevant sensitivity tests and the TEM analysis

Case Study Scenarios (CSS) 1 for OSSE of tropopause fold

&lt;p&gt;These are the simulated CAIRT ozone profiles for the period 15/Nov/2021-1/Feb/2022 using, in the following order:&lt;/p&gt;&lt;ul&gt;&lt;li&gt;CAMS hlqd control run simulation as reference ozone field&lt;/li&gt;&lt;li&gt;sim_CAIRT_grid.py to generate CAIRT retrieval grid (i.e. the geolocation of the CAIRT profiles)&lt;/li&gt;&lt;li&gt;BASCOE_MAO to interpolate CAMS hlqd 3-hourly output at CAIRT geolocation&lt;/li&gt;&lt;li&gt;FL2S to perturb CAMS@CAIRT ozone according to CAIRT expected performences (using the AK, the systematic and the random error) and add error bar to the ozone profiles.&lt;/li&gt;&lt;/ul&gt;&lt;p&gt;These are the ozone profiles assimilated by BASCOE for the Observing System Simulation Experiment (OSSE) discussed in CAIRT Report for Assessment (RfA).&lt;/p&gt