Observations of stratospheric and mesospheric O3 with a millimeter-wave radiometer at Rikubetsu, Japan

Hirofumi Ohyama,Akira Mizuno,Hideo Ogawa,Tomoo Nagahama,Hideaki Nakane

doi:10.1186/s40623-016-0406-4

Abstract

We have been measuring brightness temperature spectra of the atmospheric ozone (O3) emission at 110.83 GHz with a millimeter-wave radiometer (MWR) located at Rikubetsu, Japan, since November 1999. Tropospheric opacities, which were also measured with the MWR and were used to take into account attenuation of the O3 signal from the stratosphere and mesosphere, were corrected using the tropospheric opacity calculated from radiosonde data. Temporal variations of the measured spectral intensity of O3, likely due to degradations of the superconductor–insulator–superconductor receiver and of the vessel for cold calibration load, were also corrected using scaling factors derived from ozonesonde data up to an average height of 35 km and Microwave Limb Sounder (MLS) monthly mean climatology above the sonde height. The vertical profiles of the O3 mixing ratio in the altitude range from 24 to 56 km were retrieved from the spectra with the optimal estimation approach. The retrieval errors from uncertainties in the scaling factor, the corrected tropospheric opacity, and atmospheric temperature, as well as those from spectral noise, were evaluated, and we found that the main retrieval errors resulted from uncertainties in the scaling factor and tropospheric opacity. The retrieved O3 profiles were compared with those from the Solar Backscatter Ultraviolet (SBUV/2), the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER), and the MLS instruments onboard satellites. The retrieved O3 mixing ratios at individual levels agreed with the MLS version 3.3 or 3.4 data with an average difference better than ±5 % and a standard deviation of 4–9 %. Additionally, the retrieved O3 profiles were in reasonable agreement with the SABER version 2.0 O3 profiles and the SBUV/2 version 8.6 O3 profiles, in line with the validation results of their satellite data in the earlier literature.

Highlights

Stratospheric ozone (O3) plays an important role in protecting life on the Earth from solar ultraviolet radiation
In the analysis of the longer time series data, we find that tropospheric opacity measured with the millimeter-wave radiometer (MWR) as well as the brightness temperature of the O3 emission spectrum varied with an unnatural trend
Data screening In order to select the data that were not affected by thick cloud, we set the following condition: Nave has to be equal to Ntotal, where Nave is the number of spectra employed for calculating the hourly averaged spectrum based on the criteria described in the previous section and Ntotal is the total number of spectra measured within 1 h

Summary

Introduction

Stratospheric ozone (O3) plays an important role in protecting life on the Earth from solar ultraviolet radiation. Ohyama et al Earth, Planets and Space (2016) 68:34 constituents distributed from the middle stratosphere to the lower mesosphere, irrespective of day or night with a high temporal resolution of ~1 h, because it records an emission spectrum caused by the rotational transition of the atmospheric constituents. Such ground-based MWR measurements have been carried out at more than a dozen sites in the past decades (e.g., Daae et al 2014; Fiorucci et al 2013; Palm et al 2010; Parrish et al 2014; Schneider et al 2003; Studer et al 2012). The instrument has been tuned to the frequency of 110.836 GHz to observe the 61,5–60,6 transition of O3. Nagahama et al (2007) reported O3 observation at Rikubetsu with this instrument during the period from November 1999 to June 2002

Methods

Results

Conclusion