ENSO与青藏高原地表热力关系及所引起的下游效应
发布时间：2018-08-26 19:23
【摘要】：前期ENSO事件与青藏高原积雪异常都是影响我国夏季降水的重要因素,研究二者之间的相互联系,对我国气候预测、夏季降水预报及防灾减灾等工作具有积极、重要的意义。因此,本文依据雪深、雪水当量两套不同的高原积雪资料,结合85站高原地区的地表温度观测值、前期太平洋海温的扩展重建资料等,分析了近20年来ENSO事件对随后以积雪、地表温度要素为代表的高原地表热力状况的影响,及对应的大气环流异常和可能的物理过程,并通过数值试验进一步探讨了5-8月高原异常加热对同期大气环流的影响。研究工作主要分为以下几个部分:一、根据卫星反演的高原逐月雪深、雪水当量资料,对比分析了近20年ENSO与高原东、西部积雪的相关及持续性。研究结果如下:赤道东太平洋海温和高原东、西部雪深的相关存在明显的差异,高原西部雪深与前期11月130oW以东赤道太平洋海温的正相关可通过95%置信检验,并持续至4月,而高原东部在赤道东太平洋则一直没有对应的显著正相关区。高原东、西部雪水当量与前期11月赤道东太平洋海温相关系数的差异没有如此明显,尤其体现在4月高原东部对应在赤道东太平洋的显著正相关区可扩至160°W,但前期高原东部雪水当量与4月的自相关系数小于0.05显著性检验临界值0.46。大气环流分析结果显示,冬季厄尔尼诺成熟期至4月以前,200hPa副热带西风急流活动强盛,利于赤道东太平洋在对流层上层激发的Rossby波列沿急流传至高原上空,从而引起局地对流活动增强、雨雪增多,随着ENSO信号及作为波导的西风急流的减弱,波列趋于消失,ENSO引起的高原积雪异常也变得不显著。二、结合高原地区85站地表温度的观测值,对近20年ENSO与随后高原东部地表温度异常的相关做了进一步分析。结论如下:厄尔尼诺次年4、5月,高原东部地表温度显著偏暖,与前期Ni?o3指数的相关系数分别是0.46和0.52,通过了95%的置信检验水平,尤其5月对应在赤道东太平洋的显著正相关区甚至可伸至日界线附近。更长时间尺度上,5月高原东部75站平均地表温度与Ni?o3指数的相关系数为0.30,仍可通过0.05的显著性检验。偏暖年4-6月,高原上空200、500hPa位势高度和气温的距平都为正值,以4、5月份更为强大,偏冷年不完全相反。另外,El Ni?o次年3至4月,高原及邻近地区上空的大气环流发生明显的转换,200和500hPa层的位势高度距平由负值转为正值,500hPa气温距平也发生同样的变化,而春末高原东部地表温度的显著偏高,很可能与3月500hPa层位于里海以北的异常暖脊沿等高线向高原输送暖平流有关。La Ni?a次年未出现类似的转变。三、利用大气环流模式CAM3.1,对厄尔尼诺事件发生后高原地区的雪深、地表温度异常进行模拟分析,结果如下:1997/1998个例试验和实测海温试验均显示,CAM3.1模式无法再现出厄尔尼诺事件发生后高原地区冬、春季雪深的正异常现象,甚至与前期的统计诊断结果完全相反,但1997/1998个例试验能够较好地模拟出1、2月200hPa相对涡度的Rossby波列。而不同强度海温异常试验显示,随着厄尔尼诺事件的增强,高原地区的雪深异常仍以负值为主、且无对应的线性变化,而高原东部地表温度异常则在0附近振荡。四、利用区域气候模式,通过在青藏高原范围设置三种不同强度的大气异常加热率,讨论了5-8月青藏高原加热异常对同期大气环流的影响。结果表明:5月,以4K/day的速率加热高原大气12天后,500hPa位势高度异常在鄂霍次克海附近为正值区、我国东北及堪察加半岛以南为负值区,出现了疑似波列结构,但200hPa呈西正东负的二极分布。6月,这种波列结构更加明显,200hPa形成了完整的类Okhotsk-Japan(OKJ)波列型。但其他月份未见有类似的波列结构。7月,蒙古至鄂霍次克海及日本以东一带地区200和500hPa的负位势高度异常连成一片;8月,日本以东地区转为正值中心、鄂霍次克海附近仍维持负异常。而随着异常加热的增强,沿6月波列传播路径上的各点的位势高度异常振幅基本成比例增加。此外,射线追踪分析结果显示,5、6月份的波射线路径分布类似,模拟路径位于纬向波数为3和4对应的射线轨迹之间。
[Abstract]:Previous ENSO events and snow cover anomalies on the Qinghai-Tibet Plateau are both important factors affecting Summer Precipitation in China. Studying the relationship between them is of positive and important significance to China's climate prediction, summer precipitation prediction and disaster prevention and mitigation. The surface temperature observations in the plateau area and the data of the expansion and reconstruction of the Pacific SST in the previous 20 years are analyzed. The effects of ENSO events on the subsequent surface thermal conditions of the plateau, represented by snow cover and surface temperature elements, are discussed. The corresponding atmospheric circulation anomalies and possible physical processes are also discussed through numerical experiments. Based on the monthly snow depth and snow water equivalent data of the plateau retrieved by satellite, the correlation and persistence between ENSO and the snow cover in the East and west of the plateau in the past 20 years are compared and analyzed. The positive correlation between the snow depth in the western plateau and the SST in the eastern equatorial Pacific Ocean can be tested by 95% confidence test until April, while there is no significant positive correlation between the snow depth in the eastern plateau and the SST in the eastern equatorial Pacific Ocean. The difference of the coefficients is not so obvious. Especially, the significant positive correlation region corresponding to the eastern equatorial Pacific Ocean in April can be expanded to 160 degrees W, but the autocorrelation coefficient between the snow water equivalence in the eastern plateau and April is less than 0.46. The strong activity of the subtropical westerly jet at 00hPa contributes to the rapid propagation of the Rossby wave train over the plateau over the eastern equatorial Pacific Ocean over the troposphere, which results in the enhancement of local convective activity and the increase of rain and snow. With the weakening of ENSO signal and westerly jet as a waveguide, the wave train tends to disappear and the snow anomaly over the plateau caused by ENSO becomes unavoidable. The results are as follows: In April and May of the following year, the surface temperature in the eastern part of the plateau was significantly warmer, and the correlation coefficients with the Ni? O 3 index were 0.46 and 0.52 respectively, which passed 95% confidence test. On a longer time scale, the correlation coefficient between the mean surface temperature at 75 stations in the eastern part of the plateau and the Ni?O 3 index is 0.30, which can still pass the significance test of 0.05. In addition, from March to April of the following year, the atmospheric circulation over the plateau and its adjacent areas changed significantly, the geopotential height anomaly in the 200 and 500 hPa layers changed from negative to positive, and the 500 hPa temperature anomaly changed similarly, while the surface temperature in the eastern part of the plateau at the end of spring was obvious. The anomalous warm ridge located north of the Caspian Sea in the 500 hPa layer in March is probably related to the conveyance of warm advection to the plateau along the contour line. La Ni? A did not undergo a similar change in the following year. 3. Using the atmospheric circulation model CAM 3.1, the snow depth and surface temperature anomalies in the plateau area after the El Nino event were simulated and analyzed. The results are as follows: 1997/1998. The CAM 3.1 model can not reproduce the positive anomaly of snow depth in winter and spring in the plateau area after the El Nino event, even contrary to the previous statistical diagnostic results. However, the Rossby wave train with relative vorticity of 200 hPa in January and February can be well simulated by the 1997/1998 model. The anomaly experiment shows that with the increase of El Nino event, the snow depth anomaly in the plateau area is still dominated by negative value, and there is no corresponding linear change, while the surface temperature anomaly in the eastern plateau oscillates around 0. Fourthly, by using the regional climate model, three different atmospheric anomalous heating rates are set up over the Qinghai-Tibet Plateau, and the 5-8 anomaly is discussed. The results show that the 500 hPa geopotential height anomaly is positive in the vicinity of the Okhotsk Sea and negative in the northeast of China and south of the Kamchatka Peninsula after 12 days of heating the plateau atmosphere at a rate of 4K/day in May. In June, this kind of wave train structure became more obvious, and a complete Okhotsk-Japan (OKJ) wave train-like structure was formed at 200 hPa. However, no similar wave train structure was found in other months. In July, the negative potential height of 200 and 500 hPa from Mongolia to the Okhotsk Sea and the area east of Japan was anomalously connected; in August, the area east of Japan turned into a positive value center and the Okhotsk Sea became a positive value center. Negative anomalies are maintained nearby, and the anomalous amplitudes of potential heights along the June wave train propagation path increase proportionally with the increase of anomalous heating.
【学位授予单位】：中国气象科学研究院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P732;P461.2
本文编号：2205916
[Abstract]:Previous ENSO events and snow cover anomalies on the Qinghai-Tibet Plateau are both important factors affecting Summer Precipitation in China. Studying the relationship between them is of positive and important significance to China's climate prediction, summer precipitation prediction and disaster prevention and mitigation. The surface temperature observations in the plateau area and the data of the expansion and reconstruction of the Pacific SST in the previous 20 years are analyzed. The effects of ENSO events on the subsequent surface thermal conditions of the plateau, represented by snow cover and surface temperature elements, are discussed. The corresponding atmospheric circulation anomalies and possible physical processes are also discussed through numerical experiments. Based on the monthly snow depth and snow water equivalent data of the plateau retrieved by satellite, the correlation and persistence between ENSO and the snow cover in the East and west of the plateau in the past 20 years are compared and analyzed. The positive correlation between the snow depth in the western plateau and the SST in the eastern equatorial Pacific Ocean can be tested by 95% confidence test until April, while there is no significant positive correlation between the snow depth in the eastern plateau and the SST in the eastern equatorial Pacific Ocean. The difference of the coefficients is not so obvious. Especially, the significant positive correlation region corresponding to the eastern equatorial Pacific Ocean in April can be expanded to 160 degrees W, but the autocorrelation coefficient between the snow water equivalence in the eastern plateau and April is less than 0.46. The strong activity of the subtropical westerly jet at 00hPa contributes to the rapid propagation of the Rossby wave train over the plateau over the eastern equatorial Pacific Ocean over the troposphere, which results in the enhancement of local convective activity and the increase of rain and snow. With the weakening of ENSO signal and westerly jet as a waveguide, the wave train tends to disappear and the snow anomaly over the plateau caused by ENSO becomes unavoidable. The results are as follows: In April and May of the following year, the surface temperature in the eastern part of the plateau was significantly warmer, and the correlation coefficients with the Ni? O 3 index were 0.46 and 0.52 respectively, which passed 95% confidence test. On a longer time scale, the correlation coefficient between the mean surface temperature at 75 stations in the eastern part of the plateau and the Ni?O 3 index is 0.30, which can still pass the significance test of 0.05. In addition, from March to April of the following year, the atmospheric circulation over the plateau and its adjacent areas changed significantly, the geopotential height anomaly in the 200 and 500 hPa layers changed from negative to positive, and the 500 hPa temperature anomaly changed similarly, while the surface temperature in the eastern part of the plateau at the end of spring was obvious. The anomalous warm ridge located north of the Caspian Sea in the 500 hPa layer in March is probably related to the conveyance of warm advection to the plateau along the contour line. La Ni? A did not undergo a similar change in the following year. 3. Using the atmospheric circulation model CAM 3.1, the snow depth and surface temperature anomalies in the plateau area after the El Nino event were simulated and analyzed. The results are as follows: 1997/1998. The CAM 3.1 model can not reproduce the positive anomaly of snow depth in winter and spring in the plateau area after the El Nino event, even contrary to the previous statistical diagnostic results. However, the Rossby wave train with relative vorticity of 200 hPa in January and February can be well simulated by the 1997/1998 model. The anomaly experiment shows that with the increase of El Nino event, the snow depth anomaly in the plateau area is still dominated by negative value, and there is no corresponding linear change, while the surface temperature anomaly in the eastern plateau oscillates around 0. Fourthly, by using the regional climate model, three different atmospheric anomalous heating rates are set up over the Qinghai-Tibet Plateau, and the 5-8 anomaly is discussed. The results show that the 500 hPa geopotential height anomaly is positive in the vicinity of the Okhotsk Sea and negative in the northeast of China and south of the Kamchatka Peninsula after 12 days of heating the plateau atmosphere at a rate of 4K/day in May. In June, this kind of wave train structure became more obvious, and a complete Okhotsk-Japan (OKJ) wave train-like structure was formed at 200 hPa. However, no similar wave train structure was found in other months. In July, the negative potential height of 200 and 500 hPa from Mongolia to the Okhotsk Sea and the area east of Japan was anomalously connected; in August, the area east of Japan turned into a positive value center and the Okhotsk Sea became a positive value center. Negative anomalies are maintained nearby, and the anomalous amplitudes of potential heights along the June wave train propagation path increase proportionally with the increase of anomalous heating.
【学位授予单位】：中国气象科学研究院
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P732;P461.2
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