Simulation study for ground-based Ku-band microwave observations of ozone and hydroxyl in the polar middle atmosphere

David A Newnham,Mark A Clilverd,Pekka T Verronen,Michael Kosch,Annika Seppälä

doi:10.5194/amt-12-1375-2019

Abstract

Abstract. The Ku-band microwave frequencies (10.70–14.25 GHz) overlap emissions from ozone (O3) at 11.072 GHz and hydroxyl radical (OH) at 13.441 GHz. These important chemical species in the polar middle atmosphere respond strongly to high-latitude geomagnetic activity associated with space weather. Atmospheric model calculations predict that energetic electron precipitation (EEP) driven by magnetospheric substorms produces large changes in polar mesospheric O3 and OH. The EEP typically peaks at geomagnetic latitudes of ∼65∘ and evolves rapidly with time longitudinally and over the geomagnetic latitude range 60–80∘. Previous atmospheric modelling studies have shown that during substorms OH abundance can increase by more than an order of magnitude at 64–84 km and mesospheric O3 losses can exceed 50 %. In this work, an atmospheric simulation and retrieval study has been performed to determine the requirements for passive microwave radiometers capable of measuring diurnal variations in O3 and OH profiles from high-latitude Northern Hemisphere and Antarctic locations to verify model predictions. We show that, for a 11.072 GHz radiometer making 6 h spectral measurements with 10 kHz frequency resolution and root-mean-square baseline noise of 1 mK, O3 could be profiled over 8×10-4–0.22 hPa (∼98–58 km) with 10–17 km height resolution and ∼1 ppmv uncertainty. For the equivalent 13.441 GHz measurements with vertical sensor polarisation, OH could be profiled over 3×10-3–0.29 hPa (∼90–56 km) with 10–17 km height resolution and ∼3 ppbv uncertainty. The proposed observations would be highly applicable to studies of EEP, atmospheric dynamics, planetary-scale circulation, chemical transport, and the representation of these processes in polar and global climate models. Such observations would provide a relatively low-cost alternative to increasingly sparse satellite measurements of the polar middle atmosphere, extending long-term data records and also providing “ground truth” calibration data.

Highlights

1.1 Background informationEnergetic particle precipitation (EPP) is an important mechanism in the polar middle and upper atmosphere, causing ionisation in the neutral atmosphere and producing odd nitrogen (NOx = NO + NO2) and odd hydrogen (HOx = OH + HO2) (Brasseur and Solomon, 2005; Mironova et al, 2015; Sinnhuber et al, 2012; Verronen and Lehmann, 2013)
The proof-of-concept simulations demonstrate that changes in O3 and OH abundance in the high-latitude or polar middle and upper atmosphere, associated with geomagnetic substorm and other electron precipitation (EEP) processes, could be profiled using www.atmos-meas-tech.net/12/1375/2019/
Ground-based passive microwave measurements in the Kuband 11–14 GHz region and optimal estimation method (OEM) retrieval. At these frequencies tropospheric attenuation is small and mesospheric emission signals are transmitted to the ground with low loss

Summary

Introduction

Energetic particle precipitation (EPP) is an important mechanism in the polar middle and upper atmosphere, causing ionisation in the neutral atmosphere and producing odd nitrogen (NOx = NO + NO2) and odd hydrogen (HOx = OH + HO2) (Brasseur and Solomon, 2005; Mironova et al, 2015; Sinnhuber et al, 2012; Verronen and Lehmann, 2013). Enhanced abundances of these chemical species lead to catalytic destruction of ozone (O3) (Jackman and McPeters, 2004), perturbing the radiative balance, dynamics, and largescale circulation patterns of the atmosphere. Energetic electron precipitation (EEP), with electron energies in the range 20–300 keV, increases ionization in the polar mesosphere at altitudes of 60–90 km (Newnham et al, 2018a; Turunen et al, 2009)

Methods

Results

Conclusion