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1.
Variability of the Kuroshio path to the south of Japan plays a central role in the local climate change and exerts tremendous influences on the local atmosphere and ocean. In this study, the response of ocean dynamics, in terms of the eddy kinetic energy (EKE), potential vorticity (PV), relative vorticity, and eddy-mean flow interaction, to the Kuroshio path change is discussed. Kuroshio path south of Japan includes the near-shore non-large meander (nNLM), the off-shore non-large meander (oNLM), and the typical large meander (tLM). Analyses reveal that the distribution of EKE, PV, relative vorticity, and energy exchange between the eddy field and the mean flow respectively varies with the Kuroshio path: (1) The tLM has the maximum EKE along the path; (2) The positive and negative PV are located at the onshore and offshore side of Kuroshio axis, respevetively; (3) The distributions of anomalous relative voritcity of nNLM, oNLM, and tLM are consistent with sea surface height anomalies (SSHAs); (4) The tLM has the largest energy exchange between the eddy field and the mean flow in terms of the rate of barotropic energy conversion. On the other hand, the stability analysis of ocean currents suggests that the three Kuroshio paths south of Japan have their own intrinsic properties of the instability. 相似文献
2.
In this study, comparison of blocking climatological behaviors is presented for the two periods of 1959–1988 and 1989–2018 in a part of the Northern Hemisphere including the Atlantic Ocean, Europe and West Asia regions. Blocking events were detected using a modified blocking index that is based on vertically integrated potential vorticity. By applying this index, the characteristics of detected blocking events such as frequency, duration, intensity and area were determined and compared for both the periods.According to the results, on average, 16 and 15 blocking events per year were identified in the first and second periods, respectively. The trend analysis shows that the number of blocking events in the period 1959–1988 was significantly decreased, while it was slightly increased in the period 1989–2018. Blocking activity was most prevalent from the eastern Atlantic through Europe to West Asia, but this longitude band exhibits a relatively eastward shift in the second period. In addition, the seasonal distributions are similar to those found in previous studies with the higher occurrence of blocking events during winter and autumn seasons and the lowest frequency in summer, as well as long-lasting events and greater intensity and extension in winter than the summer time, especially in the second period. These seasonal variations of blocking frequency may be due to synoptic scale eddies and planetary waves which are more active and stronger in the colder seasons than the other seasons. On the other hand, a comparison between the two periods shows that the blocking events tend to be more frequent over West Asia especially during summer in recent years. Although discrepancies between the two periods are not significant, they could be partly due to the impacts of climate change in recent decades. 相似文献
3.
超强厄尔尼诺事件对中国东部春夏季极端降水频率的影响 总被引：2，自引：0，他引：2
利用中国国家气象信息中心提供的中国地面逐日降水0.5°×0.5°格点数据集,研究了超强厄尔尼诺事件衰减年春、夏季中国东部极端降水发生概率的变化,并通过诊断超强厄尔尼诺自身及其衍生模态各自的水汽输送和垂直运动特征,探讨了超强厄尔尼诺事件对中国东部极端降水的影响机制。结果表明,超强厄尔尼诺事件衰减年春季,整个中国东部尤其是江淮以北地区,极端降水事件发生概率显著增大。同年夏季,长江流域极端降水发生概率比常规年份高出近1倍,而在华南和华北地区则相对减小。诊断分析显示,春季超强厄尔尼诺自身及其与热带太平洋地区年循环相互作用衍生出的组合模态（C-mode）均对降水的环流背景影响显著,热带太平洋西北部低空存在强盛的反气旋性异常环流,导致大量水汽在中国东部汇聚并上升,有利于该地区极端降水事件的发生。夏季,厄尔尼诺事件已经消亡,但与C-mode影响相关联的西北太平洋异常反气旋环流仍然存在,长江流域维持极端降水事件发生的有利条件。此外,研究也显示,超强厄尔尼诺事件衰减年春、夏季中国东部对流层中上层持续有异常经向风活动,频繁的南北冷暖气流交汇可能导致强对流事件发生次数增多,这也为该区域极端降水的频发提供了支持。 相似文献
4.
This article analyzes lightning/landscape interactions across the State of Colorado. Ten years (2003–2012) of warm season cloud-to-ground (CG) lightning activity are mapped at 500 × 500 m2 to characterize the distribution of thunderstorm activity. Geospatial analyses quantify lightning activity by elevation, physiographic region, and mountain range, and time-series animations outline the general movement of thunderstorms. From these spatio-temporal perspectives, our objective is to elucidate lightning/landscape interactions as they occur over a topographically and climatologically diverse landscape. The information aids meteorologists by exposing orographic and rainshadow effects, mesoscale meteorological effects, fluxes of moisture sources, thunderstorm initiation zones, and thunderstorm movements. Other benefits extend to wildland fire managers, those who maintain lightning-vulnerable infrastructures, and, from a human risk perspective, an overall awareness to those who work and play outdoors. Major findings include (1) elevation alone does not determine the degree of lightning activity, (2) across the state's mountain ranges, lightning density varies considerably, but the number of lightning days does not, and (3) the time of lightning initiation and maxima varies by elevation, with higher mountain elevations experiencing most activity 1 h before lower mountain elevations, and 3 h before lower Great Plains locations. 相似文献
5.
本文采用K-means聚类分析的方法,将京津冀地区1979—2022年7—9月极端降水事件按照强度和位置分为四类,并在此基础上分析了此地区7—9月极端降水的环流特征、变化趋势及可能原因。通过分析不同高度层四类极端降水对应的大气环流可知,低层的西南气流、中层的副热带高压、高层的南亚高压、西风急流等天气系统以不同的配置组合共同对京津冀地区的极端降水产生影响。在长期趋势方面,1979—2022年7—9月京津冀地区的极端降水频率呈上升趋势,这是由于7月类型Ⅱ和Ⅲ极端降水的增加,以及9月类型Ⅳ极端降水的增长所致。通过对背景场的分析发现,低层水汽场及高层位势高度场有利于7月极端降水的增加,而9月类型Ⅳ极端降水的增加则源自于低层和高层背景动力场及位势高度场的增加。 相似文献
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7.
塔克拉玛干沙漠腹地大气边界层参数化方案的模拟评估 总被引：1，自引：0，他引：1
沙尘起沙、沉降、传输均受到沙漠地区大气边界层条件的制约。沙漠地区观测资料匮乏,限制大气边界层模拟效果的检验和评估。利用WRFV3.7.1中尺度数值模式中5种边界层参数化方案(ACM2、BL、MYJ、MYNN2.5、YSU),模拟2014年4月塔克拉玛干沙漠大气边界层特征,并与塔中80 m塔及风廓线雷达晴朗天气下的观测资料对比分析。结果表明:5种方案均能模拟出近地面气温及地表温度,边界层高度,感热、潜热、地表热通量的变化趋势,但未能模拟出边界层风速的日变化趋势,温风湿廓线能较好的反映晴日沙漠地区边界层结构的变化特征,但未模拟出风速随高度变化趋势。沙漠地区下垫面干燥,热容量低,晴天极易形成对流不稳定边界层,非局地湍流参数化方案,ACM2方案是沙漠地区大气边界层模拟较为合理的选择。 相似文献
8.
Winter precipitation over Central Asia and the western Tibetan Plateau (CAWTP) is mainly a result of the interaction between the westerly circulation and the high mountains around the plateau. Empirical Orthogonal Functions (EOFs), Singular Value Decomposition (SVD), linear regression and composite analysis were used to analyze winter daily precipitation and other meteorological elements in this region from 1979 to 2013, in order to understand how interactions between the regional circulation and topography affect the intraseasonal variability in precipitation. The SVD analysis shows that the winter daily precipitation variability distribution is characterized by a dipole pattern with opposite signs over the northern Pamir Plateau and over the Karakoram Himalaya, similar to the second mode of EOF analysis. This dipole pattern of precipitation anomaly is associated with local anomalies in both the 700 hPa moisture transport and the 500 hPa geopotential height and is probably caused by oscillations in the regional and large-scale circulations, which can influence the westerly disturbance tracks and water vapor transport. The linear regression shows that the anomalous mid-tropospheric circulation over CAWTP corresponds to an anti-phase variation of the 500 hPa geopotential height anomalies over the southern and northern North Atlantic 10 days earlier (at 95% significance level), that bears a similarity to the North Atlantic Oscillation (NAO). The composite analysis reveals that the NAO impacts the downstream regions including CAWTP by controlling south-north two branches of the middle latitude westerly circulation around the Eurasian border. During the positive phases of the NAO, the northern branch of the westerly circulation goes around the northwest Tibetan Plateau, whereas the southern branch encounters the southwest Tibetan Plateau, which leads to reduced precipitation over the northern Pamir Plateau and increased precipitation over the Karakoram Himalaya, and vice versa. 相似文献
9.
The onset and advance of southwest monsoon are accompanied by the appearance of the offshore trough along the southwest coast of India. This offshore trough escorts a deluge of rainfall to the southwest coast, and sometimes rainfall band moves eastward further into south India. These broad observations were noticed during the summer monsoon of June 2017. Meteorological agencies and media had reported a huge amount of rainfall over the southwest coast of India during the month. But, in the far interior of south India, rainfall was less. Due to the less rainfall, water resources depleted, which affected local farmers and common man of south India. The confused views of the common man on southwest coast rainfall could be due to lack of understanding related to various factors affecting rainfall over the same region. This article is an endeavor to address the preliminary understanding of the southwest coast rainfall during June 2017, with more stress on offshore troughs. The study begins with area-averaged rainfall statistics over south, southwest, and southeast India by employing satellite and rain gauge merged rainfall datasets. Area averaged analysis revealed offshore trough contributed 80 % of rainfall over the South West India, 68 % over South East India, contributing to an overall 75 % over south India in 2017. To identify offshore trough position and strength in the reanalysis and model simulations, a new method called VSV (Vertical Shear of Vorticity) method was introduced. The computed offshore troughs were categorized into Active, Normal, and Feeble based on the strength of meridional gradient of mean sea level pressure and 850 hPa horizontal winds. The contribution due to each category of the offshore trough over different sub-regions was investigated to find out the effect of the offshore trough to total rainfall. Dynamic and thermodynamic features of these categories of the offshore trough were investigated by using proxies like equivalent potential temperature and moisture flux convergence. We found that during active offshore trough an eastward propagation of rain bands persists, which was explained by using moisture flux convergence and equivalent potential temperature at different levels of the atmosphere. 相似文献
10.
On Multi-Timescale Variability of Temperature in China in Modulated Annual Cycle Reference Frame 总被引：2，自引：0，他引：2
The traditional anomaly (TA) reference frame and its corresponding anomaly
for a given data span changes with the extension of data length. In this study, the
modulated annual cycle (MAC), instead of the widely used climatological mean annual
cycle, is used as an alternative reference frame for computing climate anomalies to
study the multi-timescale variability of surface air temperature (SAT) in China based
on homogenized daily data from 1952 to 2004. The Ensemble Empirical Mode Decomposition
(EEMD) method is used to separate daily SAT into a high frequency component, a MAC
component, an interannual component, and a decadal-to-trend component. The results
show that the EEMD method can reflect historical events reasonably well, indicating
its adaptive and temporally local characteristics. It is shown that MAC is a temporally
local reference frame and will not be altered over a particular time span by an extension
of data length, thereby making it easier for physical interpretation. In the MAC reference
frame, the low frequency component is found more suitable for studying the interannual to
longer timescale variability (ILV) than a 13-month window running mean, which does not
exclude the annual cycle. It is also better than other traditional versions (annual or
summer or winter mean) of ILV, which contains a portion of the annual cycle. The analysis
reveals that the variability of the annual cycle could be as large as the magnitude of
interannual variability. The possible physical causes of different timescale variability
of SAT in China are further discussed. 相似文献