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1.
The Indian summer monsoon (ISM) is largely influenced by intra-seasonal variability like break and active phases of monsoon. In the present study, different cloud and aerosol parameters are considered and analyzed to formulate a cloud–aerosol coupled index (CACI) that can aid in forecasting the break phase of ISM. The method of principal component analysis is implemented to identify the significant cloud and aerosol parameters during break and active phases of ISM. The threshold ranges of each parameter are evaluated by using the normal probability density function. The result reveals that for break phase, the significant parameters are cloud water path (CWP), cloud optical depth, aerosol index, zonal wind (ZW), and meridional wind (MW) at 850 hPa pressure level whereas for active phase, the parameters found to be important are aerosol optical depth, CWP, ZW, and MW at 850 hPa pressure level. The significantly correlated (p?相似文献
2.
This study evaluates the prediction skill of stratospheric temperature anomalies by the Climate Forecast System version 2 (CFSv2) reforecasts for the 12-year period from January 1, 1999 to December 2010. The goal is to explore if the CFSv2 forecasts for the stratosphere would remain skillful beyond the inherent tropospheric predictability time scale of at most 2 weeks. The anomaly correlation between observations and forecasts for temperature field at 50 hPa (T50) in winter seasons remains above 0.3 over the polar stratosphere out to a lead time of 28 days whereas its counterpart in the troposphere at 500 hPa drops more quickly and falls below the 0.3 level after 12 days. We further show that the CFSv2 has a high prediction skill in the stratosphere both in an absolute sense and in terms of gain over persistence except in the equatorial region where the skill would mainly come from persistence of the quasi-biennial oscillation signal. We present evidence showing that the CFSv2 forecasts can capture both timing and amplitude of wave activities in the extratropical stratosphere at a lead time longer than 30 days. Based on the mass circulation theory, we conjecture that as long as the westward tilting of planetary waves in the stratosphere and their overall amplitude can be captured, the CFSv2 forecasts is still very skillful in predicting zonal mean anomalies even though it cannot predict the exact locations of planetary waves and their spatial scales. This explains why the CFSv2 has a high skill for the first EOF mode of T50, the intraseasonal variability of the annular mode while its skill degrades rapidly for higher EOF modes associated with stationary waves. This also explains why the CFSv2’s skill closely follows the seasonality and its interannual variability of the meridional mass circulation and stratosphere polar vortex. In particular, the CFSv2 is capable of predicting mid-winter polar stratosphere warming events in the Northern Hemisphere and the timing of the final polar stratosphere warming in spring in both hemispheres 3–4 weeks in advance. 相似文献
3.
利用2005~2014年10年的卫星微波临边探测仪（MLS）资料分析了热带平流层一氧化碳（CO）体积混合比的年际变率,发现热带平流层CO浓度的准两年振荡（QBO）在30 hPa高度附近存在明显的位相变化特征。大气化学气候模式模拟结果表明,热带平流层CO的准两年振荡信号是化学和动力过程共同作用的结果,而动力作用主要是QBO引起的次级经向环流引起的物质传输。化学和动力过程共同作用导致热带平流层CO浓度的垂直梯度在30 hPa高度处发生反转,进而产生一氧化碳QBO信号的位相变化。此外,化学气候模式模拟结果还表明,与CO有关的化学过程不但可以减弱一氧化碳QBO信号的振幅,还可以在热带30~10 hPa高度范围内造成一氧化碳QBO和纬向风QBO信号之间约3个月的时间差。 相似文献
4.
Inter-annual variability in the onset of monsoon over Kerala (MOK), India, is investigated using daily temperature; mean sea level pressure; winds at 850, 500 and 200 hPa pressure levels; outgoing longwave radiation (OLR); sea surface temperature (SST) and vertically integrated moisture content anomaly with 32 years (1981–2013) observation. The MOK is classified as early, delayed, or normal by considering the mean monsoon onset date over Kerala to be the 1st of June with a standard deviation of 8 days. The objective of the study is to identify the synoptic setup during MOK and comparison with climatology to estimate the predictability of the onset type (early, normal, or delayed) with 5, 10, and 15 days lead time. The study reveals that an enhanced convection observed over the Bay of Bengal during early MOK is found to shift over the Arabian Sea during delayed MOK. An intense high-pressure zone observed over the western south Indian Ocean during early MOK shifts to the east during delayed MOK. Higher tropospheric temperature (TT) over the western Equatorial Ocean during early MOK and lower TT over the Indian subcontinent intensify the land–ocean thermal contrast that leads to early MOK. The sea surface temperature (SST) over the Arabian Sea is observed to be warmer during delayed than early MOK. During early MOK, the source of 850 hPa southwesterly wind shifts to the west equatorial zone while a COL region has been found during delayed MOK at that level. The study further reveals that the wind speed anomaly at the 200-hPa pressure level coincides inversely with the anomaly of tropospheric temperature. 相似文献
5.
V. SATHIYAMOORTHY† K. MOHANKUMAR P. V. JOSEPH 《Tellus. Series B, Chemical and physical meteorology》2002,54(3):269-277
Analysis of the NCEP/NCAR reanalysis wind data shows the presence of a stationary Rossby wave in the lower stratosphere during May. This wave is seen prominently below 70 hPa level, confined between 10°N and 50°N latitudes and has a zonal wave number of 6 or 7. It is an extension into the stratosphere of the Asia Pacific Wave (APW) of the troposphere documented by Joseph and Srinivasan (1999) . As in the troposphere, in the lower stratosphere this wave shows a phase shift of 20° longitude between deficient and excess Indian summer monsoon rainfall (ISMR) years. This wave has maximum amplitude at about 200 hPa. The amplitude of the wave decreases both above and below 200 hPa level. The large-amplitude portion of this wave is thus situated in the break region between the tropical and extratropical tropopauses around 30°N latitude. It is suggested that this large-amplitude APW exchanges the tropical and extratropical airmasses through the tropopause break, making the APW signature seen in the satellite monitored total ozone (TOMS data). APW is found to exist in the following monsoon season (June to September) with the same phase as in May and its signature is also seen in that season in total ozone. 相似文献
6.
1. Introduction The quasi-biennial oscillation (QBO) of the mean zonal wind in the equatorial stratosphere was discov- ered by Reed et al. (1961) and Veryard and Ebdon (1961). Later, Funk and Garnham (1962) and Ra- manathan (1963) were the first to descri… 相似文献
7.
本文利用气候跃变的分析方法,对夏季吉林省降水量,印巴地区海平面气压距平值及500hPa高度距平值进行了分析。结果表明,它们在1967年前后均有气候跃变(或准气候跃变)出现。印巴地区夏季的海平面气压距平值和500hPa高度距平值均有超前吉林省夏季降水量一年的共同准周期变化,两者距平符号的持续性对吉林省夏季的降水有一定的影响。 相似文献
9.
Indian monsoon is the most prominent of the world’s monsoon systems which primarily affects synoptic patterns of India and adjacent countries such as Iran in interaction with large-scale weather systems. In this article, the relationship between the withdrawal date of the Indian monsoon and the onset of fall precipitation in Iran has been studied. Data included annual time series of withdrawal dates of the Indian monsoon prepared by the Indian Institute for Tropical Meteorology, and time series of the first date of 25 mm accumulated precipitation over Iran’s synoptic weather stations in a 10-day period which is the basis for the cultivation date. Both time series were considered in Julian calendar with the starting date on August 1. The studied period is 1960–2014 which covers 55 years of data from 36 meteorological stations in Iran. By classifying the withdrawal dates of the Indian monsoon in three stages of late, normal, and early withdrawals, its relation with the onset of fall precipitation in western, southwestern, southern, eastern, central, and northern regions of Iran was studied. Results demonstrated that in four out of the six mentioned regions, the late withdrawal of the Indian monsoon postpones the onset of fall precipitation over Iran. No significant relation was found between the onset of fall precipitation in central region of Iran and the monsoon’s withdrawal date. In the western, southwestern, southern, and eastern regions of Iran, the late monsoon delays the onset of fall’s precipitation; while in the south Caspian Sea coastal area, it causes the early onset of autumnal precipitation. The lag in onset of fall precipitation in Iran which is coordinated with the late withdrawal of monsoon is accompanied with prolonged subtropical high settling over Iran’s plateau that prevents the southward movement of polar jet frontal systems. Such conditions enhance northerly wind currents over the Caspian Sea which, in turn, increase the precipitation in Caspian coastal provinces, which has a different behavior from the overall response of Iran’s climate to the late withdrawal of monsoon. In the phase of early monsoon withdrawal, the subtropical jet is located at the 200 hPa level in 32.5° north latitude; compared with the late withdrawal date, it shows a 2° southward movement. Additionally, the 500 hPa trough is also located in the Eastern Mediterranean, and the MSL pressure anomaly is between ? 4 to ? 7 hPa. The Mediterranean trough in the late withdrawal phase is located in its central zones. It seems that the lack of significant correlation between late withdrawal date of Indian monsoon and late fall’s precipitation onset in the central region of Iran depends on three reasons:1. Lack of adequate weather stations in central region of Iran.2. Precipitation standard deviations over arid and warm regions are high.3. Central flat region of Iran without any source of humidity is located to the lee side of Zagros mountain range. So intensification or development of frontal systems is almost prohibited over there. 相似文献
10.
Wavelet analysis is applied to zonal mean zonal wind and temperature fields to represent characteristics of temporal periodic features different from the annual and semi-annual recurrence in the troposphere and stratosphere. A daily database of reanalyses is used for the period 1979–2008, which comprises the era of satellite-based data, as some discontinuities have been observed around 1978 in previous studies. Levels for this study have been chosen at 400 and 10 hPa, respectively in the middle troposphere and middle stratosphere. As representative for diverse latitudinal regions we have respectively selected 0°, ±20°, ±40°, ±60°, ±80°. Significant features were only found at the equator. The period of the quasi-biennial oscillation (QBO) is found to exhibit a decreasing trend in time over the 30 years studied. Potential harmonics of the QBO are found in the tropical stratosphere but also troposphere. However, they do not exhibit the same tendency. This fact supports in particular the idea that the QBO and the tropospheric biennial oscillation may be unrelated phenomena. Some of the observed features lie within the known range of variability of the El Niño Southern Oscillation. Faint effects of the 11-year solar cycle variability may have been observed in the troposphere and stratosphere, but no firm assertion may be made due to the low number of observed cycles for this kind of phenomenon in the used data-set time span. Short-term solar variabilities leave no relevant imprint. 相似文献
11.
Compared to the 50-year mean climatological value (1961–2010), the precipitation of middle-eastern Inner Mongolia exhibited a significant decrease during the past 10 years (2001–2010). To identify the climatic causes, a comprehensive investigation was conducted by inspecting climatic factors from this 50-year period, which appear to work together in connecting closely to the precipitation. Significant positive correlations with precipitation were found in sea level pressure (SLP) difference between the area of (30° N–20° S; 50–160° E) and the northeastern Pacific Ocean, between the Northern Atlantic and the northeastern Pacific Oceans, and sea surface temperature difference between the northeastern and northwestern Pacific in the previous year, while negative connections were found in the 500-hPa temperature difference between the Antarctic and the belt region around 60° S. During the period of 2001–2010, East Asia was prevailingly controlled by a huge high, which was regarded as one of unfavorable factors for producing rain or snow. Other factors were the enlarged 500 hPa temperature differences between the Antarctic and the zones around 60° S and the Equator, the negative SLP difference between the East Asia, northern Atlantic, and Pacific Oceans. Finally, the unique wind flows and associated moisture transports also played a key role in the precipitation reduction for the first decade of the twenty-first century. 相似文献
12.
Bused on January 1962-October 1993 mean value series of monthly mean temperature anomalies of 16 Antarctic stations on 10 standard isobanc surfaces from the surface to the 30 hPa,long term trends and periodic features of climate changes from the troposphere to the lower stratosphere over the Antarctic region are investigated by maximum entropy power spectrum analysis,and the relation between climate change of the stratosphere (troposphere) and tolal ozone (southern 500 hPa circulation) is discussed. 相似文献
13.
利用１９５８－１９９５年拉萨,南京地区地面至３０ｈＰａ标准等压面上月平均气温资料,研究了青藏高原主体东部的拉萨地区上空若干气候特征以及月,季,年平均气候变率随高度分布特点,并与同纬带长江三角洲的南京地区作了比较。 相似文献
14.
两类极区平流层异常增温的特征及其与850hPa温度的关系 总被引：1，自引：0，他引：1
采用NCEP/NCAR逐日再分析资料,将冬季极区平流层增温分为两种类型:Ⅰ型和Ⅱ型,并分析了两种类型增温的特征、机制及其与850hPa温度的关系。结果表明,波动强迫的强度和对流层的热量能否向上到达平流层是决定两类平流层异常增温的两个主要因素。Ⅰ型平流层增温期间,对流层也表现出了明显的增温特征,850hPa与平流层温度距平场呈现相当正压结构,极区和中纬度异常表现为反位相的振荡,呈现典型的北极涛动的特征;Ⅱ型平流层异常增温期间,增温异常仅局限在平流层范围内,平流层的中低层与高层呈现反位相的距平分布,850hPa温度距平场呈现无规则的分布特征。 相似文献
15.
Summary Latitude-altitude structure of ozone QBO over the tropical-subtropical stratosphere (40° S–40° N) has been explored by analyzing
Microwave Limb Sounder (MLS) aboard Upper Atmospheric Research Satellite (UARS) data for the period 1992–1999 using the multifunctional
regression model. The inferred ozone QBO shows two maxima located at 22 hPa and 10 hPa with coefficient of 2–3% per 10 m/s
centered at the equator. The equatorial maxima are out of phase with each other. Subtropics exhibit two peak structure near
14 hPa but of opposite sign to that of equatorial maximum near 10 hPa. Over the equatorial region, positive (zonal winds westerly)
coefficients overlay negative (zonal winds easterlies) coefficients which descend with time. A pattern of equatorial maximum
and two subtropical minima appears in the months December to February near 10 hpa and it propagates upward with progression
of seasons. Equatorial QBO is seasonally asynchronous while subtropical QBO is seasonally synchronous.
Correspondence: Suvarna Fadnavis, Physical Meteorology and Aerology Division, Indian Institute of Tropical Meteorology, Dr.
Homi Bhabha Road, Pashan, Pune 411008, India 相似文献
16.
In this paper, a diagnostic study is carried out with global analysis data sets to determine how the large scale atmospheric circulation affecting the anomalous drought of the Indian summer monsoon 2002. The daily analysis obtained from National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) for the month of July is used to investigate the mean circulation characteristics and the large scale energetics over the Indian monsoon domain. Examination of rainfall revealed that the summer monsoon (JJAS) rainfall of 2002 over India is 22% below normal in which the large deficit of 56% below normal rainfall in July. The recent past drought during summer season of 2004 and 2009 are 12 and 23%, respectively, below normal rainfall. The large deficit of rainfall in 2009 is from the June month with 48% below normal rainfall, where as 2004 drought contributed from July (19%) and August (24%). Another significant facet of the rainfall in July 2002 is lowest ever recorded in the past 138 years (1871–2008). The circulation features illustrated weak low level westerly wind at 850 hPa (Somali Jet) in July during large deficit rainfall years of 1987 and 2002 with a reduction of about 30% when compared with the excess and normal rainfall years of 1988 and 2003. Also, tropical easterly jet at 150 hPa reduced by 15% during the deficit rainfall year of 2002 against the excess rainfall year of 1988. Both the jet streams are responsible for low level convergence and upper level divergence leading to build up moisture and convective activity to sustain the strength of the monsoon circulation. These changes are well reflected in reduction of tropospheric moisture profile considerably. It is found that the maximum number of west pacific cyclonic system during July 2002 is also influenced for large deficit rainfall over India. The dynamic, thermodynamic and energetic clearly show the monsoon break type situation over India in the month of July 2002 resulting less convective activity and the reduction of moisture. The large diabatic heating, flux convergence of heat and moisture over south east equatorial Indian Ocean are also responsible for drought situation in July 2002 over the Indian region. 相似文献
17.
本文给出了平流层50hPa距平场13个特征波型和用288个格点距平资料计算的自相关系数分布图和500hPa288个格点及敏感区6个格点距平资料计算的相关系数分布图。三者之间非常相似。这意味着平流层和对流层之间是紧密相关的。50hPa自相关系数图反映的是超长波1—3波系统演变趋势,而500hPa相关系数图在秋季反映的是3波槽脊系统,冬夏季却反映的是2波系统,这足以说明50hPa距平场13个特征波型是平流层大气客观存在的运动形式。我们还发现它们在各自的季变年变过程中存在着显著的演变规律和相当长的稳定性,是大气环流未来变化和发生各种灾害性天气气候过程的重要影响因子。 相似文献
18.
Zhi-Yong Yin Yunlong Cai Xinyi Zhao Xiaoling Chen 《Theoretical and Applied Climatology》2009,97(3-4):205-218
In this study, we investigated spatial and temporal variation patterns of persistent moderate-to-heavy rainfall events in Guizhou Province of southwest China during 1951–2004. We first performed conventional frequency analysis using the annual maximum daily series at 36 weather stations fit to log-normal distribution curves. Then, we examined the frequencies of moderate-to-heavy rainfall events (>?=?20 mm/day) and persistent rainfall events (10–day running sum >?=?100 mm) during the summer season (June through August). Using principal component analysis, we identified various spatial patterns of the rainfall regime and macroscale atmospheric conditions that influence these patterns. It was found that a minor mode of variation in the 500 hPa geopotential height anomaly field over East Asia (the third principal component) had a very good relationship to the dominant regional precipitation regime (Spearman’s correlation coefficient?=?–0.623). This mode of circulation represents the N–S variation of the upper-air pressure gradients over East Asia. During its positive phase, the pressure gradient south of 40°N is reduced and accompanied by a ridge over the East China coast, while the pressure gradient north of this latitude is enhanced. Correspondingly, the study region experiences fewer persistent moderate-to-heavy rainfall events. In its negative phase, the pattern in the 500 hPa geopotential height anomaly field is reversed and the study region experiences more persistent moderate-to-heavy rainfall events. This circulation mode is related to both East Asian and Indian summer monsoons. It is also associated with the northward intrusion of the West Pacific subtropical high, the size of the circumpolar vortex over the Pacific, and the impact of the Tibetan Plateau. 相似文献
19.
Rapid development of arctic cyclone in June 2008 simulated by the cloud resolving global model NICAM
In this study, we conducted a numerical simulation of a rapid development of an arctic cyclone (AC) that appeared in June 2008 using a cloud resolving global model, Nonhydrostatic ICosahedral Atmospheric Model (NICAM). We investigated the three dimensional structure and intensification mechanism of the simulated AC that developed to the minimum sea level pressure of 971 hPa in the model. According to the result, the AC indicates a barotropic structure with a warm core in the lower stratosphere and a cold core in the troposphere. The development of the AC is accompanied by an intense mesoscale cyclone (MC) showing baroclinic structure with a marked local arctic front. The upper level warm core of the AC is formed by an adiabatic heating associated with the downdraft in the lower stratosphere. The rapid development of the AC is caused by the combination of the intensification of the upper level warm core and the merging with the baroclinically growing MC in the lower level. The merging of the AC and MC and the vertical vortex coupling with the upper air polar vortex are the most important mechanisms for the rapid development of the arctic cyclone. 相似文献
20.
Based on January 1962–October 1993 mean value series of monthly mean temperature anomalies of 16 Antarctic stations on 10
standard isobaric surfaces from the surface to the 30 hPa, long term trends and periodic features of climate changes from
the troposphere to the lower stratosphere over the Antarctic region are investigated by maximum entropy power spectrum analysis,
and the relation between climate change of the stratosphere (troposphere) and total ozone (southern 500 hPa circulation) is
discussed.
This work is supported by the research item on the Theory and Method of Long Range Weather Forecasts. 相似文献