Infrared limb-emission observations of the upper troposphere, lower stratosphere with high spatial resolution

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere - New Frontiers (CRISTA-NF) instrument has successfully taken part in the African Monsoon Multidisciplinary Analyses - Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere (AMMA-SCOUT-O3) measurement campaign in July and August 2006. Deployed on the high-altitude aircraft M55-Geophysica radiance measurements in the mid infrared are taken between about 5 and 21 km altitude with a vertical and horizontal sampling of up to 250 m and 15 km, respectively. The Juelich Rapid Spectral Simulation Code (JURASSIC) was used to retrieve the composition of the atmosphere from the radiance in the spectral range between about 776 to 868 cm$^{−1}$. A new retrieval setup and improvements of the forward model used for the retrieval allowed to obtain temperature, altitude and the volume mixing ratios of water vapor (H$_{2}$O ), ozone (O$_{3}$), nitric acid (HNO$_{3}$), peroxyacetyl nitrate (PAN), carbon tetrachloride (CCl$_{4}$) as well as aerosol extinction and a radiometric offset. Intercomparisons between CRISTA-NF data and in situ measurements from the Fast in situ Stratospheric Hygrometer (FISH) and the Fast Ozone Analyzer (FOZAN), respectively, show a good agreement. The retrieved variables are available on a grid with 500 m vertical spacing with a vertical resolution of about 500 m to 3 km below the flight altitude. Hence, information about different atmospheric trace gases and temperature are available in the upper troposphere, lower stratosphere (UTLS) region with a higher spacial resolution than today’s satellites and a better coverage than in situ measurements can provide. The simultaneous observation of trace gases mainly originating from the troposphere (like H$_{2}$O and PAN) and from the stratosphere (like O$_{3}$ and HNO$_{3}$ ), respectively, allows to determine the origin of air masses and detect mixing. The results for the test flight on 29 of July 2006 are discussed in detail. This flight started in Verona and went to the south of Italy and back, crossing twice over the subtropical jet. The CRISTA-NF observations over Italy and the Mediterranean Sea indicated that a tropopause fold was located on the northern side of the jet. Tracertracer correlation between O$_{3}$ and PAN showed the presence of mixed tropospheric and lowermost stratospheric air at this fold and around the lapsrate tropopause north of it. The structures seen in connection with this tropopause fold in the O$_{3}$ mixing ratios of CRISTA-NF were reproduced by a Chemical Lagrangian Model of the Stratosphere (CLaMS) simulation but were not found in such detail in ECMWF analysis data. These results emphasize that CRISTA-NF provides and excellent tool to observe and analyze mesoscale processes in the UTLS