I.V. Serykh, D.M. Sonechkin, V.I. Byshev, V.G. Neiman, Yu.A. Romanov
Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Nakhimovskii prospekt, 36
In this paper, we investigate the structure of geopotential height anomalies in the troposphere and lower stratosphere arising in the course Global Atmospheric Oscillation (GAO), previously detected in near-surface temperature and sea-level pressure fields.
The statistically significant differences between the opposite phases of GAO in the temperature field at the level of 1000 hPa are quite similar to those that were revealed earlier in the field of the near-surface temperature. The region of the largest temperature differences (from 1°C and up to more than 2°C) is visible in the east and in the center of the equatorial zone of the Pacific Ocean, i.e. in the canonical region of El Niño. Differences in the geopotential height field at the level of 1000 hPa form an X-shaped structure, the branches of which extend to the high latitudes of the Pacific and Atlantic Oceans and close over Eurasia and the south of the Indian Ocean. Besides, they cover a vast area above the tropics of the Indian and Atlantic oceans, Africa, the archipelago of Indonesia, Australia and the adjacent area of the Pacific Ocean within ±30° latitude.
For the level of 800 hPa, the spatial structure of the field of the average geopotential height difference remains, in general, similar to that characteristic of the level of 1000 hPa. However, the center of the X-shaped structure at this level is already beginning to collapse. On the other hand, the values of the geopotential height difference and the corresponding probability values in the east of the Indian Ocean and over area of Indonesia are slightly increasing. Values of differences in the equatorial Atlantic, northern Canada and the southeast Pacific are also increasing somewhat.
For a 500 hPa level, the global structure of the mean difference field is almost zonal. In the entire tropical belt, the average geopotential height difference exceeds 10 geopotential meters, and the values of its probabilities exceed 99%. Outside the tropical belt in the north and south of the Pacific Ocean, there are very large values of geopotential height differences (up to 30 m modulo) with a high level of statistical significance (more than 99%). The branches of the X-shaped structure, elongated to the north and south of the Atlantic are also visible, though not completely statistically significant. However, the centers of positive mean differences, corresponding to anticyclones in the south of the Pacific Ocean, in Alaska and in Canada, became even more powerful and statistically significant. Thus, the effect of the location of oceans and continents on the spatial structure of GAO is affected. Apparently, this is due to the fact that the atmospheric polar tide caused by the Chandler wobble of the poles of the Earth and the luni-solar nutation almost unobstructedly bends around the Earth, experiencing only a small topographic effect from the continents.
The zonal structure of the field of the average geopotential height difference for the 100 hPa level is even more pronounced than for the 500 hPa level. In the tropical belt, geopotential height differences exceed 30 m. All other centers of significant differences in geopotential height have become stronger in modulus. However, due to the much greater variability of the geopotential height field itself for the level of 100 hPa compared with the field for the 500 hPa level, the values of the corresponding probabilities have somewhat decreased, although the high statistical significance of some hotbeds of the highest values of the geopotential height difference in high latitudes has been preserved.
Thus, it is established that the structure of geopotential height anomalies inherent in GAO captures the entire troposphere and the lower stratosphere (up to 30 hPa). Note that with the height it becomes more zonal. At the same time, the revealed high statistical significance of these anomalies can serve as a formal evidence of their reality.
Keywords: El Niño – Southern Oscillation, Global atmospheric oscillation, geopotential heights, free
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