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- Kolbe, Marlen, et al.
(author)
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Impact of Thermohaline Variability on Sea Level Changes in the Southern Ocean
- 2021
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In: Journal of Geophysical Research - Oceans. - 0148-0227 .- 2156-2202. ; 126:9
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Journal article (peer-reviewed)abstract
- The Southern Ocean is responsible for the majority of the global oceanic heat uptake that contributes to global sea level rise. At the same time, ocean temperatures do not change at the same rate in all regions and sea level variability is also affected by changes in salinity. This study investigates 10 years of steric height variability (2008–2017) in the Southern Ocean (30°S to 70°S) by analyzing temperature and salinity variations obtained from the GLORYS-031 model provided by the European Copernicus Marine Environment Monitoring Service. The thermohaline variability is decomposed into thermohaline modes using a functional Principal Component Analysis. Thermohaline modes provide a natural basis to decompose the joint temperature-salinity vertical profiles into a sum of vertical modes weighted by their respective principal components that can be related to steric height. Interannual steric height trends are found to differ significantly between subtropical and subpolar regions, simultaneously with a shift from a thermohaline stratification dominated by the first “thermal” mode in the north to the second ’saline’ mode in the South. The Polar Front appears as a natural boundary between the two regions, where steric height variations are minimized. Despite higher melt rates and atmospheric temperatures, steric height in Antarctic waters (0–2,000m) has dropped since 2008 due to higher salt content in the surface and upper intermediate layer and partially colder waters, while subtropical waters farther north have mostly risen due to increased heat storage.
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- Lai, Y., et al.
(author)
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Impacts of the westerlies on planetary boundary layer growth over a valley on the north side of the central Himalayas
- 2021
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In: Journal of Geophysical Research - Atmospheres. - 0148-0227 .- 2156-2202. ; 126:3
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Journal article (peer-reviewed)abstract
- This study focused on planetary boundary layer (PBL) growth in winter under the influence of the westerlies over the Rongbuk Valley on the north side of the central Himalayas. Two sunny November days in 2014 with different synoptic conditions in terms of large‐scale wind direction and speed were selected to investigate the ways in which large‐scale synoptic forcing affected the vertical structure of the PBL, atmospheric stability, surface wind field, and land surface energy fluxes. This was done by using radiosonde and in‐situ measurements, the European Centre for Medium‐Range Weather Forecasts ERA5 reanalysis data set, and a one‐dimensional model. The results revealed that the valley winds and PBL growth were strongly influenced by the variations of the westerlies, which prevail in this region during the winter. When the synoptic wind direction at the height of the mountain ridges was parallel to the axis of the valley and strong, the downward transmission of the westerlies to the valley floor (DTWTV) was strong, causing high near‐surface wind speeds and sensible heat flux values. These conditions, together with a deep residual layer, unstable atmosphere, and thermally driven local wind, produced an extremely deep PBL (9 km above sea level) in the early afternoon of November 23. When the synoptic wind direction at the ridge height intersected the axis of the valley and was weak, the DTWTV was weak, and the PBL became relatively low on November 28. These results demonstrate that the interaction between the topography and synoptic circulation plays a critical role in PBL growth.
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