Improved data analysis methods for the millimetre-wave observation of strato-mesospheric ozone and winds over Northern Sweden

Sammanfattning: This thesis describes the work done to improve an ozone retrieval method. The newly implemented method aims to invert emission spectra measured with the millimetre-wave radiometers KIMRA and MIRA2 at the Swedish Institute of Space Physics (IRF) in Kiruna. In addition, the thesis presents the testing of wind retrieval capabilities that were performed in connection to the ozone retrieval method. Ozone monitoring stations are unequally distributed across latitudes despite the growing demand for measurements in remote regions, such as the Arctic. According to the Global Atmospheric Watch program, there are no registered ozone monitoring stations in Northern Sweden. Furthermore, the need for inferring mid-stratosphere to mid-mesosphere wind profiles is a consequence of the relatively poor characterization of the complex atmospheric dynamics at these altitudes by the existing monitoring techniques.  The ground-based monitoring station for trace gases at IRF is unique in Northern Scandinavia. It has the potential to investigate regional ozone distributions all-yearlong for altitudes between approximately 15 km and 55 km. KIMRA and MIRA2 are passive remote sensing instruments, and they operate in separate frequency ranges of the millimetre-wave spectral band. The radiometers were designed to continuously measure emission rates from trace gas molecules in different regions of the atmosphere. Being located in the Arctic gives the advantage of measuring ozone in the proximity of the polar vortex during the winter season.  The retrieval version presented in this thesis was developed to correct for the deviations encountered in the previous method used at IRF to infer vertical ozone profiles from measurements done with the two radiometers. Moreover, in recent years, the former method’s purpose has been shifted more towards carbon monoxide retrievals (in the case of KIMRA), which left room for upgrading and stabilizing the ozone retrievals. The advanced versions of the Atmospheric Radiative Transfer Simulator (ARTS) used as a forward model, and the embedded Optimal Estimation Method (OEM) have allowed for a more robust data analysis setup. Recent developments in ARTS have led to a rather versatile simulator with a robust numerical setup and a more straightforward control file management.  An analysis of prevailing conditions for middle atmospheric winds, together with preparations for retrievals of strato-mesospheric winds, are also discussed in this thesis. Among others, simulated retrievals and sensitivity studies based on synthetic spectra have been conducted to prepare for possible retrievals using the radiometers in Kiruna.