Intensive observations of imprints of the Oyashio (subarctic) front on the atmosphere in April 2013
Abstract
Although previous modeling studies have indicated that effects of the sea surface temperature (SST) front of Oyashio are imprinted in the subarctic atmosphere, these results had not been corroborated by in situ observations, unlike along the Kuroshio Extension (KE) front. In April 2013, during a research cruise of R/V Hakuho-maru around the Oyashio front, a total of 103 radiosondes were launched to examine atmospheric responses to the front. Composite vertical atmospheric profiles showed that stability and humidity below 1000-m height differed between the south and north sides of the front. The low-level atmosphere was stable on the northern flank, but nearly neutral on the southern flank. In the atmosphere on the southern side, a sharp drop in the relative humidity at around 1000 m suggested that the mean cloud top was at that height. Cloud base heights measured by ceilometer showed a frequency peak at 50-100 m in the north, whereas clouds were distributed at higher altitudes in the south. Turbulent heat fluxes, momentum flux, and downward longwave radiation also showed statistically significant differences across the Oyashio front.
The research vessel zonally traversed a local SST minimum with a width of approximately 400 km, where the ocean mixed layer depth is known to reach a local maximum, and we observed a large horizontal air temperature gradient below 1000-m height that corresponded to an SLP anomaly of 1.2 hPa. This was comparable to that estimated across the KE front. Furthermore, we captured rare examples of a low-level atmospheric response to warm ocean streamers. The narrow streamers moistened the air and increased the amount of aerosol particles; they thus affected even downward longwave radiation. SST fields are particularly complicated in frontal areas, and actual SST differences within a few tens of kilometers can reach more than 10°C. Recently it has been recognized that meso-scale atmospheric responses to SST on a scale of several hundred kilometers can affect basin-scale atmospheric circulations. We also need to investigate how complicated SST distributions on a scale of less than 100 km affect atmospheric simulations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS32A..05K
- Keywords:
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- 3364 Synoptic-scale meteorology;
- ATMOSPHERIC PROCESSESDE: 4215 Climate and interannual variability;
- OCEANOGRAPHY: GENERALDE: 4263 Ocean predictability and prediction;
- OCEANOGRAPHY: GENERALDE: 4504 Air/sea interactions;
- OCEANOGRAPHY: PHYSICAL