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1.
The relationship between the Spring Asian Atmospheric circulation and the previous winter Northern Hemisphere annular mode 总被引:2,自引:0,他引:2
Summary By using the NCEP/NCAR reanalysis data, the Northern Hemisphere annular mode index (NAMI), China dust storm frequency data
and China’s 160-station monthly precipitation data, the relationship between the previous winter (December–February) Northern
Hemisphere annular mode (NAM) and the following spring (March–May) Asian atmospheric circulation is examined statistically
in this study. Results demonstrate that the relationship between the spring Asian atmospheric circulation and the previous
winter NAM is more significant on decadal time scales than on interannual time scales. There are significant negative correlations
between the previous winter NAM and the spring temperature in what is almost a troposphere over Northwest China. There is
a significant positive correlation between the winter NAMI and following spring geopotential height field over the Mongolian
Plateau and Middle Siberia (MPMS) at the upper level. The positive correlation coefficients center moves to the south with
the level from high to low. At lower level the high correlation coefficients center is located over the North China. There
is a significant negative correlation between the winter NAMI and the surface horizontal wind intensity in the following spring
for Northwest China on decadal timescales. The results suggest that a strong NAM in winter is followed by a negative temperature
anomaly and a positive anomaly of the spring 500 hPa geopotential height over the MPMS, while at the same time the spring
anomaly of the southeast wind is experienced in the surface layer in Northwest China, implying that the intensity of the northwest
wind tends to weaken, and vice versa. This circulation pattern can affect the change of the spring dust storm frequency in Northwest China on decadal time scales. 相似文献
2.
春季北大西洋三极型海温异常变化及其与NAO和ENSO的联系 总被引:1,自引:0,他引:1
利用1951—2016年HadISST逐月海表温度(Sea Surface Temperature,SST)资料,NCEP/NCAR再分析资料以及1958—2016年美国伍兹霍尔海洋研究所(Woods Hole Oceanographic Institution,WHOI)提供的OAFlux数据集,运用经验正交函数分解(Empirical Orthogonal Function,EOF)和偏相关分析等统计方法,研究了春季北大西洋海温异常的主要特征及其与春季NAO和前期冬季ENSO联系。结果表明:春季北大西洋海温异常EOF的第一模态是自北而南出现的三极结构的海温距平型,其方差贡献率为35.7%。春季北大西洋三极型海温异常的形成主要受到春季NAO主导作用,还受到前期冬季热带中东太平洋海温异常的影响。消除前期冬季Niňo3.4的影响后,春季北大西洋三极型海温异常指数与同期北大西洋涛动(North Atlantic Oscillation,NAO)指数的偏相关系数分别为0.50,通过了99%置信度水平的显著性检验。消除春季NAO的影响后,春季北大西洋三极型海温异常指数与前期冬季Niňo3.4指数的偏相关系数为-0.26,通过了95%信度水平的显著性检验。春季NAO正(负)位相引起的海表风场和海表湍流热通量的异常,进而激发出正(负)位相的北大西洋三极型海温异常。前期冬季ENSO事件可以引起春季大气环流异常和热带外海温异常,进而调制春季NAO对北大西洋三极型海温异常的影响。 相似文献
3.
The aim of this paper is to re-examine and quantify a hypothesis first put forward by J. Bjerknes concerning the anomalous
coldness during the AD 1790–1820 period in western Europe. Central to Bjerknes’ hypothesis is an anomalous interaction between
ocean and atmosphere studied here using an ocean-atmosphere coupled climate model of intermediate complexity. A reconstruction
of the sea-level pressure pattern over the North Atlantic sector averaged over the period 1790–1820 is assimilated in this
model, using a recently developed technique which has not been applied to paleoclimatic modelling before. This technique ensures
that averaged over the simulation the reconstructed pattern is retrieved whilst leaving atmospheric and climatic variability to develop
freely. In accordance with Bjerknes’ hypothesis, the model results show anomalous southward advection of polar waters into
the northeastern North Atlantic in the winter season, lowering the sea-surface temperatures (SSTs) there with 0.3–1.0°C. This
SST anomaly is persistent into the summer season. A decrease in western European winter surface air temperatures is found
which can be related almost completely to advection of cold polar air. The decrease in summer surface air temperatures is
related to a combination of low SSTs and anomalous atmospheric circulation. The modelled winter and summer temperatures in
Europe compare favourably with reconstructed temperatures. Enhanced baroclinicity at the Atlantic seaboard and over Baffin
Island is observed along with more variability in the position of the North Atlantic storm tracks. The zone of peak winter
storm frequency is drawn to the European mid-latitudes.
In the original article (Climate Dynamics (2005) 24: 355-371; ) figures 4, 7, 8, 10, 11 and 13 were unfortunately incorrect. The correct version is shown here. 相似文献
4.
Summary Monthly rainfall data for 135 stations for periods varying from 25 to 125 years are utilised to investigate the rainfall
climatology over the southeast Asian monsoon regime. Monthly rainfall patterns for the regions north of equator show that
maximum rainfall along the west coasts occurs during the summer monsoon period, while the maximum along the east coasts is
observed during the northeast monsoon period. Over the Indonesian region (south of the equator) maximum rainfall is observed
west of 125 °E during northern winter and east of 125 °E during northern summer.
The spatial relationships of the seasonal rainfall (June to September) with the large scale parameters – the Subtropical Ridge
(STR) position over the Indian and the west Pacific regions, the Darwin Pressure Tendency (DPT) and the Northern Hemisphere
Surface Temperature (NHST) – reveal that within the Asian monsoon regime, not only are there any regions which are in-phase
with Indian monsoon rainfall, but there are also regions which are out-of-phase. The spatial patterns of correlation coefficients
with all the parameters are similar, with in-phase relationships occurring over the Indian region, some inland regions of
Thailand, central parts of Brunei and the Indonesian region lying between 120° to 140 °E. However, northwest Philippines and
some southern parts of Kampuchea and Vietnam show an out-of-phase relationship. Even the first Empirical Orthogonal Function
of seasonal rainfall shows similar spatial configuration, suggesting that the spatial correlation patterns depict the most
dominant mode of interannual rainfall variability. The influence of STR and DPT (NHST) penetrates (does not penetrate) upto
the equatorial regions. Possible dynamic causes leading to the observed correlation structure are also discussed.
Received October 10, 1996 Revised February 25, 1997 相似文献
5.
Upper-level cut-off lows in southern South America 总被引:2,自引:0,他引:2
Summary This paper presents a statistical study of the spatial and seasonal distribution and duration of cut-off low systems over
the southern South American region based on the NCEP- NCAR reanalysis data for the period 1979–1988. Cut-off lows were first
objectively determined as minimum geopotential values at the 250 hPa level and then subjectively imposing a cut-off circulation
and a cold core. A total of 171 cut-off low events were detected, being more frequent in austral autumn followed by winter,
spring and summer. There is a preferential region of occurrence in spring and autumn located between 68°–80° W and 30°–45° S.
The Pacific area showed the greatest frequency of occurrence followed by the Atlantic and the continental areas. Most of the
cut-off lows last 2 or 3 days (around 90% of the cases) though there is a tendency of the continental events to be longer.
The cut-off low event developed upwind the Andes on 22–28 September 1986 was selected as a case study. Low-level cold air
advection was the main forcing of the deepening of the upper level low system. 相似文献
6.
Summary The Southern South America climatological 500 hPa relative vorticity mean state was examined using regional objective analyses
of 500 hPa geopotential heights provided by the Servicio Meteorológico Nacional of Argentina. The dataset, covering the period
June 1983 to July 1987, was stratified into two samples: the cold and warm seasons. Mean cyclonic vorticity south of 40° S
results in a climatological trough over Patagonia with a northwest-southeast tilt. North of this latitude, mean anticyclonic
circulation dominates with the exception of a centre of cyclonic vorticity over the Río de la Plata (35° S, 56° W). Seasonal
changes appear to be small. Relative vorticity frequency distributions were also analysed.
The association between precipitation and synoptic-scale features of the mid-troposphere circulation was investigated through
vorticity fields. A particular distribution of vorticity anomalies associated with daily precipitation in Buenos Aires is
revealed by biserial correlation coefficient fields. In winter, the strongest relationships are found between 35° S and 40° S
over the Andes Mountains (minimum significant correlation coefficients indicating a cyclonic vorticity anomaly), and in the
south of Brazil and east of Buenos Aires over the Atlantic Ocean down to a latitude of 40° S (maximum correlation coefficients
related to anomalously anticyclonic circulation). This shows the preferential position of troughs and ridges that produce
precipitation in Buenos Aires on the time scale of a day. In summer, centres of anomalously cyclonic and anticyclonic vorticity
associated with precipitation shift slightly southward. For moderate or intense precipitation in Buenos Aires, advection of
warm and wet air southwards appears to be more important in winter, while in summer the strong anomalous vorticity gradient
north of the negative centre over the Andes Cordillera favours rainfall in Buenos Aires.
Received April 17, 1997 相似文献
7.
Coupled ocean-atmosphere surface variability and its climate impacts in the tropical Atlantic region
This study examines time evolution and statistical relationships involving the two leading ocean-atmosphere coupled modes
of variability in the tropical Atlantic and some climate anomalies over the tropical 120 °W–60 °W region using selected historical
files (75-y near global SSTs and precipitation over land), more recent observed data (30-y SST and pseudo wind stress in the
tropical Atlantic) and reanalyses from the US National Centers for Environmental Prediction (NCEP/NCAR) reanalysis System
on the period 1968–1997: surface air temperature, sea level pressure, moist static energy content at 850 hPa, precipitable
water and precipitation. The first coupled mode detected through singular value decomposition of the SST and pseudo wind-stress
data over the tropical Atlantic (30 °N–20 °S) expresses a modulation in the thermal transequatorial gradient of SST anomalies
conducted by one month leading wind-stress anomalies mainly in the tropical north Atlantic during northern winter and fall.
It features a slight dipole structure in the meridional plane. Its time variability is dominated by a quasi-decadal signal
well observed in the last 20–30 ys and, when projected over longer-term SST data, in the 1920s and 1930s but with shorter
periods. The second coupled mode is more confined to the south-equatorial tropical Atlantic in the northern summer and explains
considerably less wind-stress/SST cross-covariance. Its time series features an interannual variability dominated by shorter
frequencies with increased variance in the 1960s and 1970s before 1977. Correlations between these modes and the ENSO-like
Nino3 index lead to decreasing amplitude of thermal anomalies in the tropical Atlantic during warm episodes in the Pacific.
This could explain the nonstationarity of meridional anomaly gradients on seasonal and interannual time scales. Overall the
relationships between the oceanic component of the coupled modes and the climate anomaly patterns denote thermodynamical processes
at the ocean/atmosphere interface that create anomaly gradients in the meridional plane in a way which tends to alter the
north–south movement of the seasonal cycle. This appears to be consistent with the intrinsic non-dipole character of the tropical
Atlantic surface variability at the interannual time step and over the recent period, but produces abnormal amplitude and/or
delayed excursions of the intertropical convergence zone (ITCZ). Connections with continental rainfall are approached through
three (NCEP/NCAR and observed) rainfall indexes over the Nordeste region in Brazil, and the Guinea and Sahel zones in West
Africa. These indices appear to be significantly linked to the SST component of the coupled modes only when the two Atlantic
modes+the ENSO-like Nino3 index are taken into account in the regressions. This suggests that thermal forcing of continental
rainfall is particularly sensitive to the linear combinations of some basic SST patterns, in particular to those that create
meridional thermal gradients. The first mode in the Atlantic is associated with transequatorial pressure, moist static energy
and precipitable water anomaly patterns which can explain abnormal location of the ITCZ particularly in northern winter, and
hence rainfall variations in Nordeste. The second mode is more associated with in-phase variations of the same variables near
the southern edge of the ITCZ, particularly in the Gulf of Guinea during the northern spring and winter. It is primarily linked
to the amplitude and annual phase of the ITCZ excursions and thus to rainfall variations in Guinea. Connections with Sahel
rainfall are less clear due to the difficulty for the model to correctly capture interannual variability over that region
but the second Atlantic mode and the ENSO-like Pacific variability are clearly involved in the Sahel climate interannual fluctuations:
anomalous dry (wet) situations tend to occur when warmer (cooler) waters are present in the eastern Pacific and the gulf of
Guinea in northern summer which contribute to create a northward (southward) transequatorial anomaly gradient in sea level
pressure over West Africa.
Received: 14 April 1998 / Accepted: 24 December 1998 相似文献
8.
Summary The global distribution of the contrail coverage is computed for several scenarios of aviation in the years 2015 and 2050
and compared to 1992 using meteorological analysis data representative of present temperature and humidity conditions and
assuming 0.5% cover in a reference region 30° W–30° E, 35° N–75° N covering parts of western Europe and the North Atlantic.
The mean contrail coverage of the Earth is computed to increase by a factor of about three compared to 1992 and to reach 0.25%
in 2015. For three different scenarios of aviation and for constant climatic conditions, the global mean contrail coverage
reaches values between 0.26% and 0.75% for 2050. Contrail coverage increases more strongly than total fuel burn mainly because
of more traffic in the upper troposphere and because of more efficient engines with cooler exhaust. The overall efficiency
of propulsion is expected to grow from about 0.3 in the fleet average of 1992, to 0.4 in 2015, and to 0.5 in 2050. The expansion
of air traffic makes Canada, Alaska, the North Pacific route from North America to Japan and most of the Asian continent new
regions where contrails are expected to cover more than 0.5% on average.
Received September 7, 1998 Revised January 4, 1999 相似文献
9.
冬季北大西洋风暴轴的东西变化及其能量诊断 总被引:6,自引:4,他引:2
利用NCEP/NCAR再分析资料,定义一个风暴轴经度指数,基于这个指数做合成分析,对冬季北大西洋风暴轴63 a(1948-2010年)的东西变化特征及其能量平衡差异进行了诊断。主要结论如下:(1)北大西洋风暴轴存在明显地东扩和西退。当风暴轴向东扩展时,天气尺度瞬变波可以向下游发展至乌拉尔山以东的亚洲上空;风暴轴西退时,天气尺度瞬变波活动范围向西收缩到15°W以西的大洋上空。(2)能量诊断表明,当风暴轴向东扩展时,涡动动能在高纬度的大西洋东部及西欧上空明显增强。在0°以西的区域,涡动动能的增强主要归因于能量斜压转换过程的增强;而在0°以东区域,涡动动能的增强可能与涡动非地转位势通量引起的"下游发展效应"增强有关。风暴轴向西收缩时,变化相反。 相似文献
10.
Easterly wave regimes and associated convection over West Africa and tropical Atlantic: results from the NCEP/NCAR and ECMWF reanalyses 总被引:1,自引:0,他引:1
NCEP/NCAR and ECMWF daily reanalyses are used to investigate the synoptic variability of easterly waves over West Africa
and tropical Atlantic at 700 hPa in northern summer between 1979–1995 (1979–1993 for ECMWF). Spectral analysis of the meridional
wind component at 700 hPa highlighted two main periodicity bands, between 3 and 5 days, and 6 and 9 days. The 3–5-day easterly
wave regime has already been widely investigated, but only on shorter datasets. These waves grow both north and south of the
African Easterly Jet (AEJ). The two main tracks, noted over West Africa at 5 °N and 15 °N, converge over the Atlantic on latitude
17.5 °N. These waves are more active in August–September than in June–July. Their average wavelength/phase speed varies from
about 3000 km/8 m s-1 north of the jet to 5000 km/12 m s-1 south of the jet. Rainfall, convection and monsoon flux are significantly modulated by these waves, convection in the Inter-Tropical
Convergence Zone (ITCZ) being enhanced in the trough and ahead of it, with a wide meridional extension. Compared to the 3–5-day
waves, the 6–9-day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics.
The only main track is located north of the AEJ along 17.5 °N both over West Africa and the Atlantic. The mean wavelength
is higher, about 5000 km long, and the average phase speed is about 7 m s-1. Then the wind field perturbation is mostly evident at the AEJ latitude and north of it. The perturbation structure is similar
to that of 3–5-days in the north except that the more developed circulation centers, moving more to the north, lead to a large
modulation of the jet zonal wind component. South of the AEJ, the wind field perturbation is weaker and quite different. The
zonal wind core of the jet appears to be an almost symmetric axis in the 6–9-day wind field pattern, a clockwise circulation
north of the AEJ being associated with a counter-clockwise circulation south of the jet, and vice versa. These 6–9-day easterly
waves also affect significantly rainfall, convection and monsoon flux but in a different way, inducing large zonal convective
bands in the ITCZ, mostly in the trough and behind it. As opposed to the 3–5-day wave regime, these rainfall anomalies are
associated with anomalies of opposite sign over the Guinea coast and the Sahelian regions. Over the continent, these waves
are more active in June–July, and in August–September over the ocean. GATE phase I gave an example of such an active 6–9-day
wave pattern. Considered as a sequence of weak easterly wave activity, this phase was also a sequence of high 6–9-day easterly
wave activity. We suggest that the 6–9-day regime results from an interaction between the 3–5-day easterly wave regime (maintained
by the barotropic/baroclinic instability of the AEJ), and the development of strong anticyclonic circulations, north of the
jet over West Africa, and both north and south of the jet over the Atlantic, significantly affecting the jet zonal wind component.
The permanent subtropical anticyclones (Azores, Libya, St Helena) could help initiation and maintenance of such regime over
West Africa and tropical Atlantic. Based on an a priori period-band criterion, our synoptic classification has enabled us
to point out two statistical and meteorological easterly wave regimes over West Africa and tropical Atlantic. NCEP/NCAR and
ECMWF reanalyses are in good agreement, the main difference being a more developed easterly wave activity in the NCEP/NCAR
reanalyses, especially for the 3–5-day regime over the Atlantic.
Received: 28 May 1998 / Accepted: 2 May 1999 相似文献
11.
Summary The National Hurricane Center and Joint Typhoon Warning Center operational tropical cyclone intensity forecasts for the three
major northern hemisphere tropical cyclone basins (Atlantic, eastern North Pacific, and western North Pacific) for the past
two decades are examined for long-term trends. Results show that there has been some marginal improvement in the mean absolute
error at 24 and 48 h for the Atlantic and at 72 h for the east and west Pacific. A new metric that measures the percent variance
of the observed intensity changes that is reduced by the forecast (variance reduction, VR) is defined to help account for
inter-annual variability in forecast difficulty. Results show that there have been significant improvements in the VR of the
official forecasts in the Atlantic, and some marginal improvement in the other two basins. The VR of the intensity guidance
models was also examined. The improvement in the VR is due to the implementation of advanced statistical intensity prediction
models and the operational version of the GFDL hurricane model in the mid-1990s. The skill of the operational intensity forecasts
for the 5-year period ending in 2005 was determined by comparing the errors to those from simple statistical models with input
from climatology and persistence. The intensity forecasts had significant skill out to 96 h in the Atlantic and out to 72 h
in the east and west Pacific. The intensity forecasts are also compared to the operational track forecasts. The skill was
comparable at 12 h, but the track forecasts were 2 to 5 times more skillful by 72 h. The track and intensity forecast error
trends for the two-decade period were also compared. Results showed that the percentage track forecast improvement was almost
an order of magnitude larger than that for intensity, indicating that intensity forecasting still has much room for improvement. 相似文献
12.
Summary Spatial-temporal characteristics of temperature variations were analyzed from China daily temperature based on 486 stations
during the period 1960–2000. The method of hierarchical cluster analysis was used to divide the territory into sub-regional
areas with a coherent evolution, both annually and seasonally. Areas numbering 7–9 are chosen to describe the regional features
of air temperature in mainland China.
All regions in mainland China experienced increasing trends of annual mean temperature. The trend of increasing temperature
was about 0.2–0.3 °C/10 yr in northern China and less than 0.1 °C/10 yr in southern China. In the winter season, the increasing
trend of temperature was about 0.5–0.7 °C/10 yr in northern China and about 0.2–0.3 °C/10 yr in southern China. The increasing
trend of autumn temperature was mainly located in northwestern China and southwestern China including the Tibetan Plateau.
In spring, the rising trend of temperature was concentrated in Northeast China and North China while there was a declining
temperature trend of −0.13 °C/10 yr in the upper Yangtze River. In summer, the declining trend of temperature was only concentrated
in the mid-low valley of the Yangtze and Yellow Rivers while surrounding this valley there were increasing trends in South
China, Southwest China, Northwest China, and Northeast China.
Rapid changes in temperature in various regions were detected by the multiple timescale t-test method. The year 1969 was a rapid change point from a high temperature to a low temperature along the Yangtze River
and South China. In the years 1977–1979, temperature significantly increased from a lower level to a higher level in many
places except for regions in North China and the Yangtze River. Another rapid increasing temperature trend was observed in
1987. In the years 1976–1979, a positive rapid change of summer temperature occurred in northwestern China and southwestern
China while a decreasing temperature was found between the Yellow River and the Yangtze River. A rapid increase of winter
temperature was found for 1977–1979 and 1985–1986 in many places.
There were increasing events of extreme temperature in broad areas except in the north part of Northeast China and the north
part of the Xinjiang region. In winter, increasing temperature of the climate state and weakening temperature extremes are
observed in northern China. In summer, both increasing temperature of the climate state and enhancing temperature extremes
were commonly exhibited in northern China.
Present address: Linfen Meteorological Office, Linfen 041000, Shanxi Province, China. 相似文献
13.
Summary Anomalously wet and dry months in the Mediterranean basin were identified during the period 1860–1990 from observations at
five stations located along the west-east axis of the Mediterranean basin (Barcelona, Florence, Malta, Athens and Jerusalem),
supplemented by data from Madrid and Lisbon. Wet and dry months were characterized by hydric indices (HI) based on values
of the standardized precipitation anomalies. Different patterns of anomalously wet and dry months were qualitatively identified
on the basis of the spatial distributions of the hydric indices. The standardized sea level pressure values at 56 grid points
in the domain 35° N–65° N, 30° W–40° E, for each of the anomalously wet and dry months, were subjected to T-mode Principal
Component Analysis.
The mean hydric indices associated with each principal component in each season are arranged in four distinct different spatial
distributions for wet months and in three for dry months as following: (a) Mediterranean wide distribution of positive/negative
anomalies; (b1) Strong positive anomalies to the west, but weaker to eastern Mediterranean; (b2) Strong negative anomalies
to the west, but weaker or normal to the east; (c1) Strong positive anomalies to the west and to the east and weaker ones
to the central Mediterranean; (c2) Negative anomalies to the west and east, but weaker, or normal, or positive to the central
Mediterranean; (d) Relatively strong positive anomalies to the east and weaker ones to the western Mediterranean.
Finally, monthly mean charts of standardized anomaly and mean sea level pressure are presented for each principalcomponent
in each season. These charts are used to interpret the spatial distribution of the positive and negative precipitation anomalies
in terms of mean circulation over the domain.
Received December 10, 1998 Revised June 14, 1999 相似文献
14.
Last Glacial Maximum climate of the former Soviet Union and Mongolia reconstructed from pollen and plant macrofossil data 总被引:2,自引:2,他引:0
P. E. Tarasov O. Peyron J. Guiot S. Brewer V. S. Volkova L. G. Bezusko N. I. Dorofeyuk E. V. Kvavadze I. M. Osipova N. K. Panova 《Climate Dynamics》1999,15(3):227-240
An improved concept of the best analogues method was used to reconstruct the Last Glacial Maximum (LGM) climate from a set
of botanical records from the former Soviet Union and Mongolia. Terrestrial pollen and macrofossil taxa were grouped into
broad classes – plant functional types (PFTs), defined by the ecological and climatic parameters used in the BIOME1 model.
PFT scores were then calibrated in terms of modern climate using 1245 surface pollen spectra from Eurasia and North America.
In contrast to individual taxa, which exhibit great variability and may not be present in the palaeoassemblages, even in suitable
climates, PFTs are more characteristic of the vegetation types. The modified method thus allows climate reconstruction at
time intervals with partial direct analogues of modern vegetation (e.g. the LGM). At 18 kBP, mean temperatures were 20–29 °C
colder than today in winter and 5–11 °C colder in summer in European Russia and Ukraine. Sites from western Georgia show negative,
but moderate temperature anomalies compared to today: 8–11 °C in January and 5–7 °C in July. LGM winters were 7–15 °C colder
and summers were 1–7 °C colder in Siberia and Mongolia. Annual precipitation sums were 50–750 mm lower than today across northern
Eurasia, suggesting a weakening of the Atlantic and Pacific influences. Reconstructed drought index shows much drier LGM conditions
in northern and mid-latitude Russia, but similar to or slightly wetter than today around the Black Sea and in Mongolia, suggesting
compensation of precipitation losses by lower-than-present evaporation.
Received: 11 May 1998 / Accepted: 25 September 1998 相似文献
15.
A. P. Dimri 《Theoretical and Applied Climatology》2007,90(1-2):49-63
Summary The western Himalayas receive higher precipitation than the eastern Himalayas during the winter season (December–March). This
differential pattern of winter precipitation over the Himalayas can be attributed to topography and to a higher frequency
of disturbances over the western Himalayas, which result in variations in the circulation features. These circulation features,
in turn, result in variations in the meridional transport of heat, momentum, potential energy, and moisture across the Himalayas
due to mean and eddy motion.
Significant meridional transport due to mean motion takes place in the upper troposphere at 300 hPa and 200 hPa. Transport
east of 100° E dominates the transport over the western Himalayas. The eddy transport of heat, momentum, and potential energy
is considerably smaller than that due to mean motion. Eddy transport magnitudes are smaller up to 500 hPa and increase rapidly
aloft to 300 hPa and 200 hPa. Eddy transport over the western Himalayas is greater than over the eastern Himalayas. 相似文献
16.
East Atlantic oscillation of the atmospheric circulation 总被引:1,自引:0,他引:1
E. S. Nesterov 《Russian Meteorology and Hydrology》2009,34(12):794-800
For the period 1950–2007, the comparison is made between the indices of the East Atlantic and North Atlantic oscillations
and between the features of the atmospheric circulation and temperature regime of the Atlantic-European region connected with
various combinations of indices. The analysis is made for the factors which have caused long difference in indices in 1996–2007
and for possible causes of anomalously warm winter in Europe in 2006–2007. 相似文献
17.
Mesoscale aspects of the Urban Heat Island around New York City 总被引:15,自引:1,他引:15
S. D. Gedzelman S. Austin R. Cermak N. Stefano S. Partridge S. Quesenberry D. A. Robinson 《Theoretical and Applied Climatology》2003,75(1-2):29-42
Summary ?A mesoscale analysis of the Urban Heat Island (UHI) of New York City (NYC) is performed using a mesoscale network of weather
stations. In all seasons the UHI switches on rapidly in late afternoon and shuts down even more rapidly shortly after dawn.
It averages about 4 °C in summer and autumn and 3 °C in winter and spring. It is largest on nights with clear skies, low relative
humidity through much of the troposphere, and weak northwest winds, when it may exceed 8 °C. The synoptic meteorological situation
associated with the largest UHI occurs roughly two to three nights after cold front passages.
During spring and summer, sea breezes commonly reduce and delay the UHI and displace it about 10 km to the west. Backdoor
cold fronts, which occur most frequently in spring and early summer, reduce or even reverse the UHI, as cold air from the
water to the northeast keeps NYC colder than the western suburbs. Cases documenting the sensitivity and rapidity of changes
of the UHI to changes in parameters such as cloud cover, ceiling, and wind speed and direction are presented.
Received August 16, 2001; revised October 6, 2002; accepted November 20, 2002
Published online March 17, 2003 相似文献
18.
C. V. Singh 《Theoretical and Applied Climatology》2006,84(4):207-211
Summary In this study, Principal Component Analysis (PCA) has been used to identify the major modes of the outgoing long-wave radiation
data for the period (1979–2002) during the Indian monsoon period (June–September), using seasonal mean values over the Indian
region covering 143 grid points (5° N–35° N and 70° E–95° E at 2.5° Longitude–Latitude intervals. The five principal components
explain up to 98.0% of the total variance. The first principal component explains 60% of the total variance with a pronounced
variation in the outgoing long-wave radiation over the region 10° N to 25° N. It appears that the major reason for the monsoon
variability is the intensity and associated fluctuations in the two major semi-permanent seasonal systems. This is largely
indicative of strong seasonal shift of the major area of cloudiness associated with convergence zone. The second principal
component explaining 20% of the total variance exhibits higher positive component loadings along 25° N and east of 80° E.
The possible reason for this could be the synoptic systems such as monsoon depression/lows over the north bay and trough/vortices
off the west-coast in the Arabian sea. 相似文献
19.
Summary By analyzing 12-year (1979–1990) 200 hPa wind data from National Centers for Environmental Prediction-National Center for
Atmospheric Research reanalysis, we demonstrate that the intraseasonal time scale (30–60 days) variability of the Tropical
Easterly Jet (TEJ) reported in individual case studies occurs during most years. In the entrance region (east of ∼70° E),
axis of the TEJ at 200 hPa is found along the near equatorial latitudes during monsoon onset/monsoon revivals and propagates
northward as the monsoon advances over India. This axis is found along ∼5° N and ∼15° N during active monsoon and break monsoon
conditions respectively. Examination of the European Centre for Medium Range Weather Forecasts reanalysis wind data also confirms
the northward propagation of the TEJ on intraseasonal time scales.
During the intraseasonal northward propagations, axis of the TEJ is found about 10°–15° latitudes south of the well-known
intraseasonally northward propagating monsoon convective belts. Because of this 10°–15° displacement, axis of the TEJ arrives
over a location about two weeks after the arrival of the monsoon convection. Systematic shifting of the locations by convection,
low level monsoon flow and TEJ in a collective way during different phases of the monsoon suggests that they all may be related. 相似文献
20.
E. A. Afiesimama 《Theoretical and Applied Climatology》2007,90(1-2):103-111
Summary The paper examines the annual cycle of the mid-tropospheric easterly jet (MTJ) over West Africa against the background of
many reviews indicating different locations and characteristics of the jet and considering it as a summer feature. NCEP–NCAR
reanalysis zonal wind datasets for the period 1971–2000 and upper air datasets over the region are used. The results exhibit
realistic spatial structure of the easterly jet. The long-term mean of the datasets suggests that the jet over West Africa
is not only a summer feature but can also be found in winter with the same order of magnitude in the wind velocity at the
core. The jet axis is located at about lat. 2° N close to the Guinean Coast in winter and at lat. 14° N in summer. The meridional
oscillation of the jet suggests that as it advances northward, it maintains an altitude of 700 hPa in winter and transits
in mid-spring to 650 hPa and reaches 600 hPa in summer. In the retreat, it displaces to 650 hPa at the end of September rather
sharply to reach 700 hPa in October. The jet’s core has been observed to have a northeast–southwest orientation from season
to season, covering a longitude of 29° from its southernmost to the northernmost positions. 相似文献