Preprints
https://doi.org/10.5194/amt-2021-415
https://doi.org/10.5194/amt-2021-415

  11 Jan 2022

11 Jan 2022

Review status: this preprint is currently under review for the journal AMT.

Retrieval of the land-sea contrast of cloud liquid water path by applying a physical inversion algorithm to combined zenith and off-zenith ground-based microwave measurements

Vladimir Kostsov1, Dmitry Ionov1, and Anke Kniffka2 Vladimir Kostsov et al.
  • 1Department of Atmospheric Physics, Faculty of Physics, St. Petersburg State University, Russia
  • 2Zentrum für Medizin-Meteorologische Forschung, Deutscher Wetterdienst, Freiburg, Germany

Abstract. Combined zenith and off-zenith ground-based observations by modern microwave radiometers provide an opportunity to study horizontal inhomogeneities of the humidity field in the troposphere and of the cloud liquid water path (LWP) spatial distribution. However, practical applications are difficult and require thorough analysis of the information content of measurements, assessment of errors of data processing algorithm and the development of the quality control procedures. In this study we analyse the application of our LWP retrieval algorithm based on the inversion of the radiative transfer equation to the problem of detection of the LWP horizontal inhomogeneities by means of ground-based microwave observations in the vicinity of a coastline of a water object of medium size. The study is based on data acquired by the microwave radiometer RPG-HATPRO which is located in the suburbs of St.Petersburg, Russia, at 2.5 km distance from the coastline of the Neva Bay (the Gulf of Finland) and is operating in angular scanning mode in the vertical plane. The retrieval setup is organised in such a way that zenith and off-zenith measurements provide equal sensitivity to atmospheric parameters. The optimal elevation angles for off-zenith observations are selected. The possibility to detect LWP horizontal inhomogeneity, namely the LWP land-sea contrast, for different measurement geometries (elevation angles) and values of cloud base height is analysed. It is shown that ground-based microwave observations in the vicinity of a coastline can be a valuable tool for validation of the space-borne measurements of the LWP land-sea contrast if three principal requirements are met: (a) the multi-parameter physical inversion method is used for retrieving LWP; (b) rigorous bias correction and quality control procedures are applied to the retrieval results; (c) the information on the cloud base height is available. As a result of processing the microwave measurements at the observational site of St.Petersburg State University, the monthly-averaged values of the LWP land-sea difference have been obtained for summer months within the period 2013–2021. For 24 out of 25 months of high quality observations, the LWP land-sea monthly difference is positive (larger values over land and smaller values over water) and can reach 0.06–0.07 kg m−2. The estimations of the LWP land-sea contrast obtained from the ground-based microwave measurements at the observational site of St.Petersburg University are in very good agreement with the values of the LWP land-sea contrast obtained from the multi-year space-borne measurements by the SEVIRI instrument (Spinning Enhanced Visible and InfraRed Imager) in the region of the Neva Bay (the Gulf of Finland) in June and July. For August, the so-called “August anomaly” detected by space-borne observations is not confirmed by the ground-based measurements.

Vladimir Kostsov et al.

Status: open (until 16 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Vladimir Kostsov et al.

Vladimir Kostsov et al.

Viewed

Total article views: 124 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
102 17 5 124 3 3
  • HTML: 102
  • PDF: 17
  • XML: 5
  • Total: 124
  • BibTeX: 3
  • EndNote: 3
Views and downloads (calculated since 11 Jan 2022)
Cumulative views and downloads (calculated since 11 Jan 2022)

Viewed (geographical distribution)

Total article views: 112 (including HTML, PDF, and XML) Thereof 112 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 15 Jan 2022
Download
Short summary
Combined zenith and off-zenith ground-based observations by modern microwave radiometers provide an opportunity to study horizontal inhomogeneities of cloud cover. However, practical applications are difficult and require thorough analysis due to large variability of cloud parameters and specific observation geometry. We show principal requirements which should be met in order that the land-sea contrast of the cloud liquid water path could be successfully derived from microwave observations.