the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Sep 2024
SORAS, A ground-based 110 GHz microwave radiometer for measuring the stratospheric ozone vertical profile in Seoul
Abstract. A ground-based 110 GHz radiometer was designed to measure the stratospheric ozone vertical profile by observing the 110.836 GHz ozone emission spectrum and the instrument has been operational at Sookmyung Women’s University (37.54° N, 126.97° E) in Seoul, Korea. In this paper, we detail the instrumental design, calibration procedures, correction methods, and the retrieved ozone vertical profile. The instrument is a heterodyne total power radiometer. It down-converts the observed 110.836 GHz ozone frequency to 0.609 GHz, with a frequency resolution of 61 kHz and a bandwidth of 800 MHz. The spectral intensity is digitized using a fast Fourier transform spectrometer. For hot-cold calibration, we use microwave absorbers at room temperature and liquid nitrogen as calibration targets. Tropospheric opacity is corrected using the continuous tipping curve calibration. The measured opacities were compared with simulated values from the Korea Local Analysis and Prediction System (KLAPS) data. Additionally, since 2016, the stratospheric ozone profiles over Seoul have been demonstrated for the vertical range of 100 hPa – 0.3 hPa (16 km–70 km) with validation performed by comparing them to the ozone profiles from the MLS on AURA satellite.
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RC1: 'Comment on amt-2024-108', Anonymous Referee #2, 24 Sep 2024
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This manuscript describes a microwave radiometer that has been measuring ozone profiles from Seoul since 2016. The authors do a nice job addressing details of the measurements that are extremely important in obtaining accurate retrievals (e.g. tropospheric opacity and pointing). Understanding such details is important for any group attempting to make such measurements. I thank the authors for addressing my concerns in the initial review.
Figure 8, line 287, and conclusion – Are the tropospheric opacities shown in Figure 8 for KLAPS and SORAS calculated at precisely the same time? It is not clear whether the higher summer opacity of the KLAPS results come from periods when SORAS opacity measurements are not possible because of the high opacity. In the conclusion the authors say that the O3 bias relative to MLS is different during the summer than during other seasons, but in order to establish this a clear plot showing the difference in tropospheric opacity biases is needed.
Paragraph starting on line 382 and conclusion - While the authors are correct in attributing a portion of the observed negative bias to the use of an AC240 spectrometer, this is not thought to cause an altitude dependence in the bias. Just as for the instrument presented here, the Sauvegeat study does show an altitude dependence in the bias between that ground-based instrument and MLS. But, as for the instrument discussed in the Sauvegeat study, the altitude dependence of that bias is only weakly, if at all, caused by the AC240 (their Table II, last column). This should be noted in the text.
Lines 305 and 409 – What velocity does a 55 kHz doppler shift imply? Is this physically realistic? Is the 55 kHz smaller than the expected error of the local oscillators used in the instrument?
Line 343 – ‘bacause’ should be ‘because’Citation: https://doi.org/10.5194/amt-2024-108-RC1
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