| Based on the daily reanalysis data of ECMWF (ERA-40) and global ice and sea surface temperature (GISST), detailed investigation is conducted on the spatio-temporal evolution of eastern storm tracks and its possible mechanism, the major conclusion is drawn are as follows:(1) As viewed from month to month, polycentric distribution, most typical with two or three centers whose possibility could reach to even94.7%high, is a common occurred phenomenon for the intensity maxima of the storm track, which is most often appeared in the spring season while least in the autumn and winter seasons, whereas polycentric distribution with four or more centers is most often appeared in the summer season.(2) If the storm track with the strongest center located to the east of160°W is defined as the eastern-pattern storm track, as composed to the eastern storm track which means the eastern part (160°W-120°W) of north Pacific storm track, then the eastern-pattern storm track, generally with33%chance, is most often appeared in the summer season, especially in July, while least in the winter season, especially in January and February.(3) As viewed from the vertical structure, the track intensity can be strongest over the eastern part of the north Pacific storm track, but not for the baroclinic transport of poleward and upward energy by the transient eddies.(4) The intensity of the eastern part of the north Pacific storm track throughout the troposphere shows an increase long-term trend in44years from1957to2001, which is prominent in summer but not in winter.(5) EOF result shows that it does exist some difference under different condition when the seasonal, regional and track type effects are taken into consideration, but a few unique feature is still revealed in the variation of the eastern part of the north Pacific storm track, e.g., wherein the major EOF modes are not always one-by-one corresponding to the counterparts over the entire north Pacific storm track. In the winter as an example, there are notable interannual variations of eastern storm track: the first mode depicts a meridional seesaw variation over the storm track whereas the second mode depicts the variation of the storm track against its climatological position, and the third mode depicts tri-polar oscillator.(6) The result of energy diagnosis analysis shows that on the basis of the climate average, the baroclinic conversion of eddy potential energy to the eddy kinetic energy is the main source of synopitic scale eddies in the eastern north Pacific storm track, whereas the effect of ageostrophic geopotential flux divergence is relatively not significant, and the barotropic dispersion of the time average kinetic energy conversion to eddy kinetic energy is the main dissipation.(7) Regression analysis shows that when eastern storm track shift southward (northward), in the same time, there exhibit an El Nino (La Nina) pattern in the sea surface temperature (SST) anomaly, a unusual low (high) over the tropic and North Pacific colder (warmer) sea surface, and a positive (negative) PNA teleconnection pattern in the middle troposphere; and when eastern storm track strengthen (weaken), in the same time, the SST of Kuroshio colder (warmer) than ordinary, over the colder (warmer) sea surface is unusual low (high), a positive (negative) WP teleconnection pattern appears in the middle troposphere; and when eastern storm track show the positive-negative-positive (negative-positive-negative) tri-polar oscillator, the SST nearby of Papua New Guinea warmer (colder), and SST nearby of Hawaii is colder (warmer), and in the middle troposphere is a similar positive (negative) PNA teleconnection. The time coefficients of modes have significant correlation with Aleutian Low index, PNA index, WP index, Nino3index and the Kuroshio Current index respectively, which demonstrate the existence of the relationship betwween the eastern storm track and atmosphere and SST abnormalies. |
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