Papers in Meteorology and Geophysics

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   Zonal symmetric atmospheric motions are dominant in the tropical latitudes, suggesting that the meridional mass transport there depends largely on Hadley-type circulation. Simulated movements of air parcels were analyzed in low latitudes under ideal axially symmetric conditions to evaluate the contribution of this meridional circulation to interhemispheric exchanges.
   A three-dimensional atmospheric general circulation model was modified into an axially symmetric model. It demonstrated that a cross-equatorial mass exchange often takes place easily as air parcels reach a simulated inter tropical convergence zone (ITCZ).
   Unsteady components of atmospheric northward or southward motions are important for a cross-equatorial mass exchange, and meridional asymmetry of the Hadley circulation due to displacement of the ITCZ from the equator greatly influences the characteristics of a mass exchange, such as the amount of exchangeable air mass and the mass exchange time.
   The mass exchange time in simulated ideal Hadley circulations was estimated to be 0.1 to 0.2 yr. The model in this study is ideal axially symmetric, so this exchange time scale should not be applied directly to 3-D global models or the real world. However, it is very interesting and important that this time scale is much shorter than those obtained from conventional analyses of the observed distribution of minor constituents, and that the idealized Hadley circulation induced in the model tropics performs a more efficient interhemispheric exchange.

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An automatic method of determining the focal mechanism solution is proposed. This method includes picking initial motion polarity of P waves and judging reliability of the solution. The method of picking initial motion polarity of P waves is as follows. First, Bessel band-pass filter is applied. Then, by using an AR model, arrival time of P wave initial motion is detected and AR filter is applied. To determine a focal mechanism solution, a grid search method is used. For judging reliability of the solution, it is evaluated synthetically, for example, from stability of the solution and focal mechanism solutions of earthquakes which occurred about there. It is shown that about 70 percents of initial motion polarity picked by Japan Meteorological Agency (JMA) can be picked by applying this method. Moreover, the ratio of inconsistent polarities between those picked in this study and picked by JMA is less than 3.5 %. Judging from this, automatic picking of initial motion polarity works with sufficient accuracy. Furthermore, by applying this method, more than 2.8 times focal mechanism solutions obtained by JMA are determined with sufficient reliability. Occasionally, focal mechanism solutions of inland shallow earthquakes, which are less than 2.0 in magnitude, or of deep earthquakes, whose magnitude can not be calculated because of their smallness, can be determined with sufficient reliability. Applying this method, focal mechanism solutions can be effectively determined with sufficient reliability.

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