The results show that a warm high ridge at the middle level and transformed surface cold high over the plain provide a good background condition ; a cooling process produced by net surface radiation fluxes is the trigger and strengthening mechanism for the fog event ; the subsidence flow at the middle and low tropospheric levels is favorable for the setting - up and maintenance of stable stratification at the boundary layer and weak wind condition at the ground layer over the fog region ; the transportation of weak warm advection at lower levels and weak lift motion at the boundary layer play a very important role to the long maintenance of the fog event ; the intrusion of north wind accompanied by cold advection is a main dynamic factor of the fog dissipation 結(jié)果表明:在中高層暖性高壓脊及地面變性冷高壓穩(wěn)定維持的大尺度背景條件下,地表凈輻射引起的近地層冷卻是大霧過(guò)程的觸發(fā)和加強(qiáng)機(jī)制;中低空下沉氣流的存在有助于近地層的弱風(fēng)條件和穩(wěn)定層結(jié)的建立;低層暖平流的輸入和邊界層的淺層抬升是大霧長(zhǎng)時(shí)間持續(xù)的原因;伴隨冷空氣南下的偏北大風(fēng)是驅(qū)使大霧消散的動(dòng)力因子。
There are two parts in this paper : firstly , a set of single doppler velocity models are presented for typical ambient windfields that include those of being uniform horizontally , macroscale convergence and divergence , which overlap warm and cold advection . which are marked by different signatures in the single doppler velocity field . the models proposed can help users identify useful information from the dopple velocity patterns 本論文包括兩個(gè)部分:第一篇通過(guò)對(duì)典型風(fēng)場(chǎng)的單多普勒天氣雷達(dá)徑向速度圖象進(jìn)行模擬,典型風(fēng)場(chǎng)包括水平均勻一致的風(fēng)場(chǎng)、非均勻水平風(fēng)場(chǎng)的大尺度運(yùn)動(dòng)的輻合輻散風(fēng)場(chǎng)以及大尺度運(yùn)動(dòng)的輻合輻散風(fēng)場(chǎng)與冷暖平流的迭加等。