10:45 AM - 12:15 PM
[AAS10-P02] Influence of the tropics-extratropics boundary and sea surface temperature fronts on the latitude of the westerly jet stream
Keywords:tropics-extratropics boundary, sea surface temperature front, westerly jet stream
In the tropical and midlatitude atmospheres, large-scale dynamics are governed by different dominant physical processes. The tropics is governed by the weak temperature gradient system where temperature gradient is constrained to be moderate, whereas the midlatitude area is governed by the quasi-geostrophic system where the Coriolis force and pressure gradient force are nearly balanced. Presumably, in order for these two different governing equations to be simultaneously valid in large scales, the boundary between these two regions must be connected by phenomena with small spatial scales. Therefore, in this study, we investigate the atmospheric behavior at the tropics-extratropics boundary in the Northern Hemisphere.
The 5800 m height line at the 500 hPa level is defined as the tropics-extratropics boundary. This line serves as a proxy for the northern edge of the tropical region. Next, we focus on the strong wind axis of the westerly jet stream, which moves meridionally at mid-latitudes, because the jet stream can supply vortices with small spatial scales. Then, we examine the positional relationship between the jet stream and the tropical mid-latitude boundary.
By measuring the mean latitudinal distance between the jet stream and the boundary, it is shown that the jet stream flows near tropics-extratropics boundary in most seasons. However, only in seasons when a sea surface temperature (SST) front exists near the boundary, the westerly jet stream is trapped above the SST front and temporarily leaves tropics-extratropics boundary. In boreal spring and autumn, when the westerly jet stream is anchored by the SST front, the existence of mesoscale phenomena such as the Meiyu-Baiu front may be required to connect the tropical and midlatitude solutions in place of the westerly jet stream.
The 5800 m height line at the 500 hPa level is defined as the tropics-extratropics boundary. This line serves as a proxy for the northern edge of the tropical region. Next, we focus on the strong wind axis of the westerly jet stream, which moves meridionally at mid-latitudes, because the jet stream can supply vortices with small spatial scales. Then, we examine the positional relationship between the jet stream and the tropical mid-latitude boundary.
By measuring the mean latitudinal distance between the jet stream and the boundary, it is shown that the jet stream flows near tropics-extratropics boundary in most seasons. However, only in seasons when a sea surface temperature (SST) front exists near the boundary, the westerly jet stream is trapped above the SST front and temporarily leaves tropics-extratropics boundary. In boreal spring and autumn, when the westerly jet stream is anchored by the SST front, the existence of mesoscale phenomena such as the Meiyu-Baiu front may be required to connect the tropical and midlatitude solutions in place of the westerly jet stream.