SUBMITTED TO WEATHER AND FORECASTING
This paper describes two well developed barrier jets that formed in the northeastern Gulf of Alaska, near the town of Yakutat. During the cooler months of the year barrier jets are a common occurrence in Yakutat as warm moist air from the south and southwest is blocked by the very steep terrain of t...
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| Format: | Text |
| Language: | English |
| Published: |
2000
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.525.7297 http://pafc.arh.noaa.gov/papers/yak_jets.pdf |
| Summary: | This paper describes two well developed barrier jets that formed in the northeastern Gulf of Alaska, near the town of Yakutat. During the cooler months of the year barrier jets are a common occurrence in Yakutat as warm moist air from the south and southwest is blocked by the very steep terrain of the St. Elias Range. One of the important results of this study is that the typical Yakutat barrier jet develops when warm mid-level tropospheric air moves over the St. Elias Range. This warm air produces very high values of static stability at mountain crest levels. In addition, there is little evidence of the formation of a dome of cold air on the windward side of the St. Elias Range during barrier jet episodes. This could be due to 1) the low resolution of the surface observations in the region, or 2) it may indicate that additional processes are operative in cases where the terrain is extremely steep. If the latter is true, than blocking upstream of the St. Elias Range may occur because of dynamic processes. Strong summit-level cross-barrier flow could generate upstream propagating gravity waves, which would in turn decelerate low-level onshore flow. As a consequence, a region of high pressure would be produced over the windward slopes, which may create a barrier-parallel wind jet if the synoptic and meso-scale pressure gradients are large enough. During the onset and dissipation of barrier jets it is common for the surface winds at Yakutat airport to remain light, while between 300 m and 1500 m the winds are on the order of 15-25 m s-1. In addition, pressure differences between Yakutat and other coastal stations give a rough indication of strong barrier jet winds, but are not in general highly correlated with surface wind speeds at Yakutat. As a result of this study, a simple conceptual model of the life cycle of Gulf of Alaska barrier jets is presented. |
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