Measurement capabilities of strato-mesospheric winds in the Arctic region

There is a need for inferring mid-stratosphere to mid-mesosphere wind profiles between approximately 25 and 75 km altitude as a consequence of the relatively poor characterization of the complex atmospheric dynamics at these altitudes by the existing monitoring techniques. A better knowledge of the wind field could help improve the quality of global circulation models for this region of the atmosphere. Our goal is to measure strato-mesospheric horizontal wind profiles over the Arctic region. To this objective, we are using data from continuous measurements recorded for ozone chemistry monitoring purposes that have been ongoing since 2002 and from dedicated wind measurements recorded since 2014. An accurate interpretation of the wind patterns could give us an insight into past and present wind dynamics in the Arctic. For the measurements, we are using the ground-based millimeter-wave radiometer KIMRA [Raffalski et al., 2002] with a spectral range between 195-233GHz, situated at the Swedish Institute of Space Physics, in Kiruna, Sweden. Within KIMRA’s spectral range, the thermal emission spectrum of a strong ozone line at 231.3GHz has been used for ozone monitoring, and it might also be the most suitable to use for inferring wind speeds. It has both a strong contribution compared to other, secondary gases identified in this frequency region, and it has an enhanced spectral signature compared to the baseline effects induced by the radiometer itself. By determining the difference between the observed (wind-affected) and the simulated reference spectra (without wind), we can characterize the Doppler shift of the line with the help of our retrieval system and subsequently infer the speeds of the winds that induced the shift. The wind profile retrievals are performed with the Qpack2 package [Eriksson et al., 2005] for inverting the set of observations using an optimal estimation retrieval approach (OEM). The OEM provides the best solution given the measurements and their errors and the a priori knowledge and its errors. The a priori knowledge that we consider has been estimated from ERA5 re-analysis data downloaded from the Copernicus Climate Data Store. In connection with Qpack2, we use the Atmospheric Radiative Transfer Simulator (ARTS-2) [Bühler et al., 2018] as a forward model. We test the retrieval capabilities of strato-mesospheric horizontal wind profiles and assess if the retrieval can be performed with sufficient accuracy. In addition, we intend to evaluate the technical capabilities of KIMRA regarding possible improvements to the instrument’s performance. Besides the implementation of new hardware, we will analyze how adjusting certain parameters that currently limit its spectral resolution affects the sensitivity of the measurements. Furthermore, we will aim to decrease the intrinsic noise of the radiometer and increase its stability over time.

How to cite: Kajtár, R. E., Milz, M., Raffalski, U., and Mendrok, J.: Measurement capabilities of strato-mesospheric winds in the Arctic region , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-187, https://doi.org/10.5194/egusphere-egu2020-187, 2019