For the first time, vertical water vapour profiles were measured in the Central Arctic North of 85°N during the MOSAiC campaign (Multidisciplinary drifting Observatory for the Study of Arctic Climate). Continuous measurements of the Raman lidar PollyXT are used to retrieve high-resolved vertical profiles of the water vapour mixing ratio (WVMR) during the polar night. The collected data are calibrated and evaluated by use of selected clear-sky profiles between 25 October 2019 and 29 February 2020.
Three different calibration methods are applied using reference data from radiosonde launches or microwave radiometer (MWR) measurements, respectively. The calibration with the least error results from a linear fit between collocated radiosonde and lidar measurements and delivers a final calibration constant of 15.96 ± 0.37 g/kg for the period from 25 Oct 2019 to 29 Feb 2020.
The calibrated WVMR profiles are analysed regarding the vertical distribution of water vapour in the Arctic, its impact on the downward thermal-infrared radiation (DTIR) at the surface, and its relation to the Arctic Oscillation (AO) index as a measure for the general atmospheric circulation.
The Arctic atmosphere is very dry during the winter time with WVMR values below 2 g/kg. The vertical water vapour distribution is strongly related to the temperature profile. Layers with higher WVMR values are often capped by temperature inversions. Layers with higher integrated water vapour values (IWV) are located either close to the surface (coupled) or in an elevated layer (decoupled), related to local or advective processes, respectively.
The impact of the vertical distributed water vapour on the clear-sky DTIR at the surface was investigated by evaluating the evolution of the air mass at the measurement location over several hours for seven clear-sky cases. The relation between the measured DTIR at the surface and the lidar IWV shows a linear correlation for each case, but with a shift in the radiation values depending on the temperature of the vertical distributed water vapour. The impact of the IWV on the DTIR is determined to be 9.33 − 15.03 W/kg from the example cases. Beside, a linear correlation is found between the temperature of the vertical distributed water vapour and the radiation temperature of the sky, which is derived from the Stefan-Boltzmann’s Law. Both results depict the high impact of the atmospheric water vapour profile on the surface energy budget during clear-sky winter conditions.
The influence of the atmospheric circulation on the vertical water vapour distribution in the Arctic is investigated by use of the AO index. While very stable conditions with a weak exchange with lower latitudes are expected during the positive phase of the AO, a stronger meridional transport is related to the negative phase of the AO. The evaluation of 71 randomly selected clear-sky profiles shows differences in the amount and the vertical structure of each WVMR profile between the two phases. Higher WVMR values and layers with higher IWV are observed during the negative AO phase. Nonetheless, a high variability between dry and humid cases is seen during all phases of the AO due to synoptic events. Two main sources for water vapour in the Eastern Central Arctic are identified independent of the AO. These are cyclones on the one hand and the occurrence of a main wind direction from the seas north of Siberia namely Laptev, Kara and Barents Sea on the other hand.
In summary, the thesis discusses different calibration methods for the derivation of WVMR profiles from Raman lidar measurements in its first part. In the second part, the thesis gives an overview over the vertical water vapour distribution in the Central Arctic winter and its complex relation to temperature profiles, radiation measurements at the surface and the atmospheric circulation.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:84548 |
| Date | 04 April 2023 |
| Creators | Seidel, Clara |
| Contributors | Universität Leipzig, Leibniz-Institut für Troposphärenforschung |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:masterThesis, info:eu-repo/semantics/masterThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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