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The daily patterns and activity of Intertropical Convergence Zone(ITCZ) in the Western-Central Pacific Ocean are analyzed using NOAA interpolated Outgoing Longwave Radiation dataset during the period from 1979 to 2008, and the relationships between ITCZ patterns and Arctic Oscillation(AO) is investigated in this paper. In accordance with the central activity region the daily ITCZ can be divided into six patterns—north, south, equator, double, full and weak pattern, respectively. The statistic result shows that the north(accounting for 30.98% of the total observations), south(31.11%) and weak(24.05%) ITCZ patterns are the most active daily patterns within a 30-year period, while the other three ITCZ patterns occur infrequently. Results show that the February-April AO index has a significant positive(negative) correlation with the frequency of the north(weak) ITCZ pattern from March-May to August-October, with the strongest correlation in April-June(March-May). At the same time, the lower tropospheric atmosphere circulation(850-hPa wind field) and SST anomalies corresponding to the AO change significantly in the tropical Pacific. When AO is in the positive phase, there is an anomalous westerly from the equator to 15°N and warmer SST in the critical north ITCZ active region, while there is an anomalous easterly and insignificant change of SST from the equator to 15°S. The wind and SST anomalies share the same characteristics of the equatorial asymmetry and thus enlarge the gradient between the south and north of equator, which would help reinforce convection in the north of equator and result in more frequent occurrence of the northern type of ITCZ. 相似文献
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1—3月北极涛动对北半球热带太平洋和大西洋对流活动的可能影响 总被引：1，自引：0，他引：1
利用1979—2008年日分辨率的向外长波辐射资料以及NCEP再分析资料,去除ENSO影响后,分析了1—3月北极涛动对热带太平洋和热带大西洋对流活动及降水的可能影响。结果表明北极涛动偏强(弱)时,热带太平洋和大西洋对流活动显著偏强(弱)。北半球热带大洋冬季平均向外长波辐射与北极涛动指数的相关系数存在两个显著负相关区:一个位于中太平洋区,大致包括13°—20°N、160°E—170°W;另外一个位于热带大西洋,显著区覆盖的范围大体包括5°—20°N、15°—70°W。这些区域的降水量也表现出显著的正相关。向外长波辐射、强对流面积指数、强对流强度指数、平均降水量等指标与北极涛动指数的相关均以冬季同期最高,随时间滞后相关迅速减弱。与此对应的对流层低层大气环流也有显著变化,850hPa风场的变化表现为热带太平洋有异常的气旋性环流,气旋中心区与显著强对流和降水异常区一致。而热带大西洋有显著的经向环流辐合和风切变,与异常对流和降水区吻合。海洋模式的模拟结果表明,与北极涛动有关联的海温分布,很大程度上与大气强迫有关,说明热带1—3月降水和对流活动与海温的关联较弱。北极涛动与热带太平洋、大西洋对流和降水活动之间主要是通过大气环流的变动产生联系的。 相似文献
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针对所摄路面影像,本文提出了基于梯度方向的车道线提取方法。车道线上边缘点的梯度方向大体与本车道线垂直,据此我们可以将车道线上的边缘点从所有边缘点中分离出来,再将这些点拟合,得到车道线。实验结果表明,本文方法具有很好的鲁棒性,对复杂路面的车道线提取效果较好。 相似文献
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2—4月北极涛动对中西太平洋ITCZ活动的可能影响 总被引：1，自引：0，他引：1
利用1979—2008年逐日向外长波辐射(OLR)资料以及北极涛动(AO)指数,从日尺度上分析了中西太平洋上赤道辐合带(ITCZ)的类型及活跃程度,并研究其与AO的关系。结果表明:在日尺度上ITCZ存在不同的强对流中心,依据中心位置可以划分为北、南、赤道、双、全和弱等六种型态,其中北、南和弱型ITCZ在日尺度上频次最高,分别占总天数的30.98%、31.11%和24.05%,而赤道、双和全型ITCZ出现频次较少。AO与西北太平洋ITCZ活动的相关分析表明,2—4月AO指数与北型ITCZ频次存在显著正相关,相关系数达到0.49,而与弱型ITCZ频次存在显著负相关,相关系数为-0.42。当AO处于正(负)位相时,从同期至8—10月北型ITCZ活跃程度偏强(弱),而弱型ITCZ偏弱(强),在滞后1～2个月时相关达到最高。此外低层环流场以及SST也存在显著变化。当AO为正位相时,中西太平洋上赤道至15 °N范围内存在异常西风气流,SST异常偏暖。这也加大了南北向SST梯度,导致赤道以北辐合加强,对流活跃,北型ITCZ频次增多。这表明AO可能是通过风场和SST来影响北型ITCZ的活动,这种海气相互作用产生的影响具有较长的持续性。 相似文献
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中国南方冬季异常低温和降水事件 总被引：6，自引：1，他引：5
This paper analyzed the anomalous low-temperature events and the anomalous rain-abundant events in January since 1951 and winter since 1880 for southern China.The anomalous events are defined using ±1σ thresholds.Twelve cold Januaries are identified where temperature anomaly below-1σ,and ten wet Januaries are identified where precipitation anomaly above +1σ.Among these events there are three patterns of cold-wet Januaries,namely 1969,1993 and 2008.The NCEP/NCAR reanalysis data are used to check the atmospheric circulation changes in association with the anomalous temperature and precipitation events.The results show that the strong Siberian High(SBH),East Asian trough(EAT) and East Asian jet stream(EAJS) are favorable conditions for low-temperature in southern China.While the anomalous southerly flow at 850 hPa,the weak EAT at 500 hPa,the strong Middle East jet stream(MEJS) and the weaker EAJS are found to accompany a wetter southern China.The cold-wet winters in southern China,such as...更多 January of 2008,are mainly related to a stronger SBH,and the circulation in the middle to upper troposphere is precipitation-favorable.In wet winters,the water vapor below 500 hPa is mainly transported by the anomalous southwesterly flow and the anomalous southern flow over the Indo-China Peninsula and the South China Sea area.The correlation coefficients of MEJS,EAMW(East Asian meridional wind) and EU(Eurasian pattern) to southern China precipitation in January are +0.65,-0.59 and-0.48 respectively,and the correlations for high-pass filtered data are +0.63,-0.55 and-0.44 respectively,the significant level is all at 99%.MEJS,EAMW and EU together can explain 49.4% variance in January precipitation.Explained variance for January and winter temperature by SBH,EU,WP(west Pacific pattern) and AO(Arctic Oscillation) are 47.2% and 51.5%,respectively.There is more precipitation in southern China during El Nio winters,and less precipitation during La Nia winters.And there is no clear evidence that the occurrence of anomalous temperature events in winter over southern China is closely linked to ENSO events. 相似文献
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多种东亚冬季风指数及其与中国东部气候关系的比较 总被引：2，自引：0，他引：2
利用NCEP/NCAR再分析资料及气温和降水观测资料,对比分析了12种不同定义的东亚冬季风(EAWM)指数及其与中国东部冬季温度和降水的关系。结果显示:多数EAWM指数具有较好的一致性,同时也存在差异,体现了不同定义的指数反映东亚冬季风整体性和局部性特征的侧重点有所不同。有10个EAWM指数均反映出近60年东亚冬季风呈减弱趋势,尤其是近30年最为明显,平均减弱速率达-0.25σ/10a,各指数均有强烈的年际变率和年代际波动。有10个(8个)EAWM指数与我国东部冬季温度(降水)第1模态呈显著负相关;其中西伯利亚高压指数对冬季温度年际变率方差解释率最高(53.3%),而对降水年际变率方差解释率最高的是对流层中高层东亚经向风指数(50.4%)。此外,不同EAWM指数与温度和降水的对应关系在El Niňo状态、La Niňa状态有不同的变化,表明在利用单个EAWM指数监测冬季气候时,要考虑到各个指数在ENSO不同状态下具有的差异性参考意义。 相似文献
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遥感数字图像直方图的标准化常用于不同时相相邻遥感图像的拼接和进行土地利用变化监测的预处理,还可以消除不同成像条件对图像分析的影响,部分纠正由于太阳/传感器位置或大气影响造成的相邻图像的辐射误差,从而达到相同成像条件的效果。由于常用的基于数值统计学的直方图的标准化方法不能达到理想效果,该文提出了基于无变化像素进行图像标准化的方法,通过多光谱图像差异直方图及每一波段黑灰白像素的相关系数计算,自动选择无变化像素,进而进行直方图的标准化。将该方法应用于2期TM图像遥感数据,明显减小了成像条件差异,提高了数字图像标准化的有效性。 相似文献
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中国东部夏季云量与日气温统计关系 总被引：1，自引：0，他引：1
利用中国东部1980-2009年130个测站夏季逐日气象资料,定量分析无雨日条件下云量与气温统计关系,从辐射角度解释成因。结果表明:日最高气温、日平均气温大多随着云量增多而显著下降,这主要是由于云量增加会导致到达地面的太阳总辐射和地表净辐射显著减少。日最低气温在北方随着云量增多而显著上升;在南方则随着总云量、低中云量增多而显著下降,但与高云量的关系不明确。出现这种现象的原因无法完全从云量影响辐射的角度进行解释。气温日较差随着云量增多而显著减小,并且北方减小的幅度大于南方。 相似文献
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