This content is not published

Characterisation of particulates in the upper troposphere/lower stratosphere

Thu, 12/09/2021 - 09:43
Start Date: 
End Date: 
Programme Reference: 
Forschungszentrum Jülich

The Process Exploration through Measurement of infrared and millimetre-wave Emitted Radiation (PREMIER) instrument was proposed to ESA within the framework of the 7th Earth Explorer Call. The instrument was designed to quantify dynamic, radiative, and chemical processes in the upper troposphere and lower stratosphere (UTLS) that control the global atmospheric composition. During the PREMIER study phase clouds and aerosol were not considered as retrieval targets, but recent research results indicated that the infrared limb sounding instrument (IRLS) part or PREMIER has a high, but to some extend unexplored, potential of measuring particles in the UTLS. Within this study four tasks were defined to 1) identify the scientific and operational objectives, 2) generate representative test cases, 3) investigate the IRLS sensitivity towards cloud and aerosol and the spatial detection capabilities, and 4) investigate the IRLS microphysical retrieval capabilities.
In the Task Note 1 the technical key specifications of PREMIER IRLS are presented and the current state of understanding and measurements for UTLS ice clouds, aerosol and polar stratospheric clouds (PSCs) are summarized. Scientific and operational objectives for measuring cirrus, aerosol, and PSCs are elaborated individually. In Task Note 2 representative test cases that were used to study the IRLS aerosol and cloud measurement capabilities are presented and the corres- ponding radiance spectra were simulated for the IRLS chemistry (IRLS-CM) and dynamics mode (IRLS-DM), and the Michelson Interferometer for Passive Atmo- spheric Sounding (MIPAS). The Representative test cases comprise simulations for sulfate aerosol, volcanic ash, ice clouds, ultra thin ice clouds, and PSCs. In Task Note 3 the spatial detection capabilities of IRLS were investigated and the detection sensitivity range was derived based on simulated spectra. The results were compared to MIPAS simulations and the detection schemes were verified using MIPAS measurements. It was found that IRLS spatial detection is significantly better than for MIPAS, and compared to other space-based limb sounding aerosol measurements the spatial sampling, the global, and temporal coverage are bet- ter. Concerning the detection sensitivity IRLS can fill a sensitivity gap between UV/VIS limb and IR nadir measurements. The lower detection limit is clearly smaller than the detection maximum of SAGE II and the upper detection limit is above the lower detection limit of IR nadir measurements. In Task Note 4 studies focusing on the classification of aerosol, ice clouds, and PSCs and the retrieval of microphysical properties with IRLS are presented. It was found that similar to IR nadir measurements ash can be separated from ice clouds. Moreover the IRLS is also sensitive to sulfate aerosol and PSC that were also found to be classifiable with IRLS. Microphysical retrieval to derive ice water content, particle concentration, extinction, and particle size were developed and show microphysical information can be derived for optically thin limb direction ice clouds, PSCs, and aerosol.
The results of this study show that IRLS aerosol and cloud measurements can provide additional information on particles in the UTLS, such as thin cirrus, aerosol, and PSCs that are not detectable for the wealth of present and future atmospheric sounding instruments.

Application Domain: 
Generic Technologies