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1.
Summary Monthly rainfall conditions in Israel were determined, using data from 12 stations, during 30 years (1961–90). The definition
of a month to be dry, normal or wet, was done using standardized rainfall totals. Pressure departures for each of the three rainfall categories for each month
of the rainy season, were calculated and mapped. Correlation between rainfall totals at each of the 12 stations and monthly
mean sea level pressure at 72 grid points in the area delimited by the 20° W and 50° E meridians and the 20° N and 60° N parallels,
was performed. For each month, 12 correlation maps were prepared (one of each station). Similar maps were averaged together
to form coherent rainfall regions. At the beginning of the rainy season (October) the rainfall in Israel is sporadic and spotty
without a distinctable coherent region. At the end of the rainy season (April) the rainfall is more widespread, forming a
large coherent region covering most of the country.
Dry rainfall conditions in Israel, were found to be characterized by positive pressure departures in the eastern Mediterranean
and over Israel and/or by easterly or southerly circulation over the eastern Mediterranean. Wet rainfall conditions in Israel,
were found to be characterized by negative pressure departures in the eastern Mediterranean and over Israel and/or by westerly
or northerly circulation over the eastern Mediterranean. Moreover, in many cases dry conditions in Israel, were associated
with below normal pressure conditions over central or western Europe, while wet conditions in Israel, with above normal conditions
over the same region, thus, reflecting the so-called Mediterranean Oscillation. Finally, normal rainfall conditions are characterized by very slight to negligible pressure departures over the entire Mediterranean
and Europe.
Received November 18, 1997 Revised March 3, 1998 相似文献
2.
Summary ?A calendar of the negative and positive phases of the North Sea – Caspian Pattern (NCP) for the period 1958–1998 was used to analyse the implication of the NCP upper level teleconnections on the regional climate of the eastern Mediterranean basin. Series of monthly mean air temperature
and monthly total rainfall from 33 stations across Greece, Turkey and Israel, for the same period, were used. For each month,
from October to April, averages of the monthly mean temperatures and the monthly rainfall totals as well as the standardized
values of both parameters were calculated separately for the negative (NCP (−)) and the positive (NCP (+)) phases of the NCP.
At all stations and in all months, temperature values were significantly higher during the NCP (−) as compared with the NCP (+). Furthermore, apart from very few exceptions, the absolute monthly mean maximum and monthly mean minimum values were
obtained during the NCP (−) and the NCP (+) phases, respectively. The maximum impact of the NCP on mean air temperature was detected in the continental Anatolian Plateau, where the mean seasonal differences are around 3.5 °C. This influence decreases westwards and southwards.
The influence on the rainfall regime is more complex. Regions exposed to the southern maritime trajectories, in Greece and
in Turkey, receive more rainfall during the NCP (−) phase, whereas in the regions exposed to the northern maritime trajectories, such as Crete in Greece, the Black Sea region in Turkey, and in all regions of Israel, there is more rainfall during the NCP (+) phase. The accumulated rainfall differences between the two phases are over 50% of the seasonal average for some stations.
A comparison of the capabilities of the NCP, the North Atlantic Oscillation (NAO) and the Southern Oscillation (SO) indices to differentiate between below and above normal temperatures was made. The results have placed the NCP, as the best by far of all three teleconnections in its ability to differentiate between below or above normal temperatures
and as the main teleconnection affecting the climate of the Balkans, the Anatolian Peninsula and the Middle East. These results may serve to downscale General Circulation Model (GCM) scenarios to a regional scale and provide forecasts
regarding eventual temperature and/or precipitation changes.
Received June 25, 2001; revised February 25, 2002; accepted March 3, 2002 相似文献
3.
Precipitation (P) and freshwater (E-P) fluxes at the air-sea interface are investigated in the Atlantic Ocean sector using the reanalyses of the European Centre
for Medium Range Weather Forecasts (ERA) and of the National Centers for Environmental Prediction (NCEP). A canonical correlation
analysis method between these fields and sea level pressure (SLP) is used to identify patterns. We also test whether precipitation
and freshwater fluxes can be reconstructed from SLP data. In the winter months, patterns associated with both the North Atlantic
Oscillation (NAO) and the East Atlantic (EA) mode are identified. The signals are strong enough to be reconstructed from the
reanalysis fields, and they correspond to a significant part of the variability. The NAO signal is more robust than the EA
one. The NAO-related variability mode is also present when the monthly precipitation rate is averaged for the winter season
and even for annual averages. However, in the later case, other variability of natural origin (for instance, ENSO variability)
or noise from the model and assimilation system prevents the reconstruction of E-P associated with NAO from SLP variability. Difficulties are identified in the tropical Atlantic with a different behaviour
of NCEP and ERA precipitation variability, especially near the Inter Tropical Convergence Zone (ITCZ). The ERA patterns suggest
a NAO signature in the tropical Atlantic which has clear monthly patterns and indicates a link between the phase of NAO and
changes in the position and intensity of ITCZ. However, the analysis of winter rainfall based on satellite and in situ data
does not support the monthly tropical pattern of ERA precipitation although it suggests a relation between convection near
15°S and NAO during northern winter.
Received: 10 February 2000 / Accepted: 7 May 2001 相似文献
4.
Summary An upper level atmospheric teleconnection between grid points: 0°, 55° N; 10° E, 55° N (North Sea) and 50° E, 45° N; 60° E,
45° N (northern Caspian) was identified. This teleconnection, referred as the North Sea-Caspian Pattern (NCP) is evident at the 500 hPa level. The NCP is more pronounced during winter and the transitional seasons. An index (NCPI) measures the geopotential heights differences between the two poles of the NCP. Time series of the NCPI are presented and analysed. Except for September, no significant temporal trends were found. Negative and positive phases
of the NCP (NCP(−) and NCP(+), respectively) were defined using standardized scores. A classification of all months into NCP(−), NCP(+) or normal conditions during the analysis period (1958–1998) was prepared and analysed. No significant correlation was
found between the NCPI and the NAO index. The anomalous circulation during either NCP(−) or NCP(+) conditions is defined and its possible impact on the regional climate is discussed. Preliminary results show below normal
temperatures and above normal precipitation in the Balkans and the Middle East during NCP(+), and the opposite for NCP(−).
Received March 8, 2001 Revised July 3, 2001 相似文献
5.
Summary The west coast of the Indian peninsula receives very heavy rainfall during the summer Monsoon (June–September) season with
average rainfall over some parts exceeding 250 cm. Heavy rainfall events with rainfall more than 15 cm day−1 at one or more stations along the west coast of India occur frequently and cause considerable damage. A special observational
programme, Arabian Sea Monsoon Experiment, was carried out during the monsoon season of 2002 to study these events. The spatial
and temporal distributions of intense rainfall events, presented here, were used for the planning of this observational campaign.
The present study using daily rainfall data for summer monsoon season of 37 years (1951–1987) shows that the probability of
getting intense rainfall is the maximum between 14° N–16° N and near 19° N. The probability of occurrence of these intense
rainfall events is high from mid June to mid August, with a dip in early July. It has been believed for a long time that offshore
troughs and vortices are responsible for these intense rainfall events. However, analysis of the characteristics of cloud
systems associated with the intense rainfall events during 1985–1988 using very high resolution brightness temperature data
from INSAT-IB satellite shows that the cloud systems during these events are characterized by large spatial scales and high cloud tops.
Further study using daily satellite derived outgoing longwave radiation (OLR) data over a longer period (1975–1998) shows
that, most of these events (about 62%) are associated with systems organized on synoptic and larger scales. We find that most
of the offshore convective systems responsible for intense rainfall along the west coast of India are linked to the atmospheric
conditions over equatorial Indian Ocean. 相似文献
6.
M. Jury H. Rautenbach M. Tadross A. Philipp 《Theoretical and Applied Climatology》2007,88(3-4):169-177
Summary Spatial scales of variability in seasonal rainfall over Africa are investigated by means of statistical and numerical techniques.
In the statistical analysis spatial structure is studied using gridded 0.5° resolution monthly data in the period 1948–1998.
The de-seasonalized time series are subjected to successive principal component (PC) analysis, allowing the number of modes
to vary from 10 to 24, producing cells of varying dimension. Then the original rainfall data within each cell are cross-correlated
(internal), then averaged and compared with the adjacent cells (external) for each PC solution. By considering the ratio of
internal to external correlation, the spatial scales of rainfall variability are evaluated and an optimum solution is found
whose cell dimensions are approximately 106 km2. The aspect of scale is further studied for southern Africa by consideration of numerical model ensemble simulations over
the period 1985–1999 forced with observed sea surface temperatures (SSTs). The hindcast products are compared with observed
January to March (JFM) rainfall, based on a station-satellite merged analysis of precipitation (CMAP) data at 2.5° resolution.
Validations for different sized areas indicate that cumulative standardized errors are greatest at the scale of a single grid
cell (104 km2) and decrease 20–30% by averaging over successively larger areas (106 km2). 相似文献
7.
Monthly sea surface temperature anomalies (SSTA) at near-global scale (60 °N–40 °S) and May to October rainfall amounts in
West Africa (16 °N–5 °N; 16 °W–16 °E) are first used to investigate the seasonal and interannual evolutions of their relationship.
It is shown that West African rainfall variability is associated with two types of oceanic changes: (1) a large-scale evolution
involving the two largest SSTA leading eigenmodes (16% of the total variance with stronger loadings in the equatorial and
southern oceans) related to the long-term (multiannual) component of rainfall variability mainly expressed in the Sudan–Sahel
region; and (2) a regional and seasonally coupled evolution of the meridional thermal gradient in the tropical Atlantic due
to the linear combination of the two largest SSTA modes in the Atlantic (11% with strong inverse loadings over the northern
and southern tropics) which is associated with the interannual and quasi-decadal components of regional rainfall in West Africa.
Linear regression and discriminant analyses provide evidence that the main July–September rainfall anomalies in Sudan–Sahel
can be detected with rather good skills using the leading (April–June) or synchronous (July–September) values of the four
main oceanic modes. In particular, the driest conditions over Sahel, more marked since the beginning of the 1970s, are specifically
linked to the warm phases of the two global modes and to cold/warm anomalies in the northern/southern tropical Atlantic. Idealized
but realistic SSTA patterns, obtained from some basic linear combinations of the four main oceanic modes appear sufficient
to generate quickly (from mid-July to the end of August) significant West African rainfall anomalies in model experiments,
consistent with the statistical results. The recent negative impact on West African rainfall exerted by the global oceanic
forcing is primarily due to the generation of subsidence anomalies in the mid-troposphere over West Africa. When an idealized
north to south SSTA gradient is added in the tropical Atlantic, strong north to south height gradients in the middle levels
appear. These limit the northward excursion of the rainbelt in West Africa: the Sahelian area experiences drier conditions
due to the additive effect (subsidence anomalies+latitudinal blocking) while over the Guinea regions wet conditions do not
significantly increase, since the subsidence anomalies and the blocking effect act here in opposite ways.
Received: 26 June 1997 / Accepted: 3 October 1997 相似文献
8.
R. D'Arrigo E. Cook R. Villalba B. Buckley J. Salinger J. Palmer K. Allen 《Climate Dynamics》2000,16(8):603-610
The limited length and spatial coverage of instrumental climate data for many areas of the Southern Hemisphere impedes the
study of atmosphere-ocean dynamics prior to the past century. Such analyses are important for understanding interannual to
decadal variation of the Southern Hemisphere circulation and whether recent changes are related to anthropogenic effects rather
than natural variability. We use a middle- to high-latitude tree-ring width data set (from Tasmania, New Zealand and Tierra
del Fuego) to reconstruct sea-level pressure (SLP) variability spanning the Tasman Sea and vicinity since ad 1740. The variables reconstructed are austral summer (November–March) SLP for Hobart, Tasmania (43°S, 147°E) and the Chatham
Islands, New Zealand (44°S, 177°E), as well as a meridional circulation index (Hobart-Chatham Islands index) which measures
the pressure gradient between these two stations. The three reconstructions are well verified statistically and capture between
40 and 48% of the variance in the SLP data. The instrumental and estimated SLP show similar spatial patterns of correlation
with the sea surface temperature (SST) field for the Pacific. Statistically significant (above 95% level) 3–3.5 year spectral
peaks are identified in the three reconstructions using multitaper spectral analysis, and a significant 4–5 year peak is found
in both the Chatham Islands and Hobart-Chatham Islands SLP reconstructions. These two modes are within the bandwidth of the
El Nino-Southern Oscillation. Although very speculative, they may also correspond to a proposed Antarctic circumpolar wave
of SLP, SST, wind and sea-ice extent, believed to play a key role in atmosphere-ocean circulation for the Southern Hemisphere.
Received: 30 November 1998 / Accepted: 13 December 1999 相似文献
9.
Variations in the Temperature Regime Across the Mediterranean During the Last Century and their Relationship with Circulation Indices 总被引:2,自引:2,他引:0
Summary Circulation types were identified by means of zonal and meridional indices calculated separately over ten different regions
of 20°×20° over the Mediterranean and Europe. Seasonal temperature trends in 22 grid boxes of 5°×5° covering the entire Mediterranean,
and at six stations Lisbon, Madrid, Florence, Luqa (Malta), Athens and Jerusalem, were calculated.
A warming trend in the period 1873–1989 was detected. The warming is more evident in the western Mediterranean with an average
rate of about 0.4 [°C/100 yr], than in the eastern Mediterranean with an increase of only 0.2 [°C/100 yr]. A cooling trend
in autumn in the eastern Mediterranean with an average rate of −0.5 [°C/100 yr] was detected and attributed to an increase
in northerly meridional circulation in that region.
Warming trends at Lisbon, Madrid, Florence, Athens and Jerusalem, were more important than the trends in the grid boxes containing
these stations. This rapid warming was attributed to urban effects. No such effects were found in Luqa due to its location
and the lack of urban effects there.
Temperatures at Luqa, Athens and Jerusalem are highly positively correlated. Likewise, temperatures at Lisbon and Madrid.
Temperatures at Florence are either correlated with Madrid or with Luqa. Negative or no correlations were found between Lisbon
or Madrid with Athens or Jerusalem, except during the winter. This was attributed to the fact that favourable circulation
for high temperatures in the eastern stations was opposite to the favourable circulation for high temperatures in the western
stations and vice versa.
Finally, the above reinforces the concept of a Mediterranean Oscillation between the western and eastern basins.
Received November 14, 1997 Revised June 2, 1998 相似文献
10.
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
11.
The impact of the PBL scheme and the vertical distribution of model layers on simulations of Alpine foehn 总被引:1,自引:0,他引:1
Summary This paper investigates the influence of the planetary boundary-layer (PBL) parameterization and the vertical distribution
of model layers on simulations of an Alpine foehn case that was observed during the Mesoscale Alpine Programme (MAP) in autumn
1999. The study is based on the PSU/NCAR MM5 modelling system and combines five different PBL schemes with three model layer
settings, which mainly differ in the height above ground of the lowest model level (z
1). Specifically, z
1 takes values of about 7 m, 22 m and 36 m, and the experiments with z
1 = 7 m are set up such that the second model level is located at z = 36 m. To assess if the different model setups have a systematic impact on the model performance, the simulation results
are compared against wind lidar, radiosonde and surface measurements gathered along the Austrian Wipp Valley. Moreover, the
dependence of the simulated wind and temperature fields at a given height (36 m above ground) on z
1 is examined for several different regions.
Our validation results show that at least over the Wipp Valley, the dependence of the model skill on z
1 tends to be larger and more systematic than the impact of the PBL scheme. The agreement of the simulated wind field with
observations tends to benefit from moving the lowest model layer closer to the ground, which appears to be related to the
dependence of lee-side flow separation on z
1. However, the simulated 2 m-temperatures are closest to observations for the intermediate z
1 of 22 m. This is mainly related to the fact that the simulated low-level temperatures decrease systematically with decreasing
z
1 for all PBL schemes, turning a positive bias at z
1 = 36 m into a negative bias at z
1 = 7 m. The systematic z
1-dependence is also observed for the temperatures at a fixed height of 36 m, indicating a deficiency in the self-consistency
of the model results that is not related to a specific PBL formulation. Possible reasons for this deficiency are discussed
in the paper. On the other hand, a systematic z
1-dependence of the 36-m wind speed is encountered only for one out of the five PBL schemes. This turns out to be related to
an unrealistic profile of the vertical mixing coefficient.
Correspondence: Günther Z?ngl, Meteorologisches Institut der Universitat München, 80333 München, Germany 相似文献
12.
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
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.
Summary Degree-days as a measure of accumulated temperature deviations from a base temperature have many practical applications in
various human related activities such as home cooling, heating, plant growth in agriculture and power generation in addition
to energy requirement. Long temperature records are necessary for their reliable estimations at given stations. In this paper,
degree-day measure has been applied to monthly temperature records for systematically changed base temperature values from
− 25 °C to + 35 °C with 5 °C increments at 255 meteorology stations in Turkey. The results are represented in the form of
spatial degree-day distribution maps, which are then related to various climatic, meteorological and topographic features
of Turkey. For instance, free surface water bodies in forms of surrounding seas, lakes and rivers insert retardation in the
expansion of heating degree-days over large regions. On the other hand, cold air penetration from polar regions in the northeastern
Turkey originating from Siberia appears at moderate base temperature heating degree-days.
Received August 20, 1998 Revised June 21, 1999 相似文献
15.
Summary Two UV-Biometer 501A instruments were used to estimate global erythemal irradiance at two locations in southwest Sweden;
the Earth Sciences Centre, University of G?teborg (57.69° N; 11.92° E) and the island of Nordkoster, 200 km to the north (58.83° N;
10.72° E).
A semi-empirical radiative transfer model was used to calculate the global erythemally effective irradiance under clear skies.
A ratio of the hourly measured to clear-sky modelled irradiance was then derived for zenith angles 35–70°. Subsequent comparisons
were then made with routine measurements of sunshine duration at G?teborg and sunshine duration, cloud cover, type and height
at Nordkoster.
Cloud transmission of UV-B irradiance decreases with increasing solar zenith angle, with cloud attenuation being 8% stronger
at Nordkoster Island for zenith angles >>;60°. Transmission also decreases with increasing cloud cover such that overcast
cloud conditions reduce transmissions by an average of 75%. In addition, cloud type affects the amount of ground incident
irradiant flux. Fractus cloud afforded the least UV-B transmission (0.16), while cirrus filaments afforded the most (0.95).
The spatial and temporal distribution of clouds appears tobe non-random. Under conditions of 1 to 3 octas, sky cover, clouds
appear to be concentrated in line with the sensor and Sun on more occasions than that expected given a random cloud distribution.
The same cloud cover condition also resulted in many instances of ground incident irradiance above clear-sky values. The presence
of cumuliform clouds appears to increase the likelihood of the latter phenomena.
Received January 4, 1998 相似文献
16.
F. Mkankam Kamga 《Theoretical and Applied Climatology》2000,67(1-2):97-107
Summary Four coupled atmosphere-ocean general circulation models were examined for the ability of their control runs to simulate
present climate given present forcings. The area of study is mainly Cameroon and some of its surrounding areas (0–25° E, 5° S-30° N).
These models are from the UK Meteorological Office Hadley Centre (HadCM2), the German Max-Planck-Institut für Meteorologie
(ECHAM4), the Canadian Centre for Climate Modelling and Analysis (CGCM1) and the Australian Commonwealth Science and Industrial
Research Organisation (CSIRO-Mk2). The ability of the models to reproduce the observed spatial and temporal patterns was studied.
ECHAM4 and HadCM2 were found to reproduce the spatial pattern well, with a correlation of more than 90%. They also simulated
the main annual features of both temperature and rainfall. The CSIRO-Mk2 model was slightly less successful and the CGCM1
had the worst results for the area, especially as concern rainfall. In view of these results, ECHAM4 and HADCM2 were used
to evaluate projected changes in rainfall and temperature resulting from increased concentration of greenhouse gases in the
atmosphere for the 30 year period 2040 to 2070.
Received February 15, 1999/Revised March 10, 2000 相似文献
17.
B. Alijani 《Theoretical and Applied Climatology》2002,72(1-2):41-54
Summary In order to explore the spatial and temporal variations of 500 hPa flow patterns and their relationship with the climate
of Iran, monthly mean geopotential heights for the region 0° E to 70° E and 20° N to 50° N, at 5 degree resolution, were analysed.
The study period covered the winter months October to March during the period 1961–90. The monthly height of the 500 hPa level
was averaged along each meridian from 25° N to 45° N. The height of the mean monthly pressure pattern was mapped against the
study years. The results showed that the characteristics of the 500 hPa flow pattern varied over monthly and annual time scales.
Principal Component Analysis, with S-mode and Varimax rotation, was also used to reduce the gridded data to 5 (6 in October)
significant factors. The factor scores for each month were then correlated with monthly Z-scores of precipitation and temperature
anomalies over Iran. The results showed that troughs and ridges located close to Iran had more influence on the climate of
Iran. Two troughs were identified and named the Caspian and Syrian troughs.
Received April 12, 2001 Revised July 24, 2001 相似文献
18.
E. Bednorz 《Theoretical and Applied Climatology》2008,92(3-4):133-140
Summary Daily circulation patterns responsible for heavy snowfalls in the Polish – German lowlands were analysed. Composite maps of
sea level pressure (SLP) and 500 hPa geopotential height means and anomalies were constructed for the days with an increase
in snow cover depth by ≥5 cm. Contour maps show negative anomalies of SLP and 500 hPa level over central Europe, indicating
a low pressure system. Strong positive anomalies of SLP appear over Scandinavia and the northern Atlantic with the centre
of positive anomalies located over Iceland. Weaker negative anomalies are observed in the Azores region. This confirms the
strong negative correlation between snow cover appearance and the North Atlantic Oscillation index in Europe. The days with
heavy snowfalls were clustered using the Ward’s method. Three types of circulation patterns were distinguished, each of them
characterised by a low pressure system over central Europe. Type 3 represents the northern position of the low with its centre
over the Baltic Sea, Type 2 shows the southern position of the low with its centre over the Adriatic and the Ionic Sea and
Type 1 represents the low location between the two previous patterns with a wide meridional trough over the Atlantic.
Author’s address: Ewa Bednorz, Institute of Physical Geography and Environmental Planning, Adam Mickiewicz University, ul.
Dzięgielowa 27, 61-680 Poznań, Poland. 相似文献
19.
H. Kraus C. M. Ewenz M. Kremer J. M. Hacker 《Meteorology and Atmospheric Physics》2000,73(3-4):157-175
Summary In Southern Australia summertime deep cold fronts are frequently preceded by a shallow cold frontal line connected to a prefrontal
lower tropospheric trough. The advance of this line defines a “cool change” which in many cases causes severe weather events.
The goal of this paper is to analyze the multi-scale structure of these cool changes using aircraft observations and synoptic-scale
analyses. The aircraft measurements on cross-frontal tracks of horizontal lengths of up to 300 km are performed with an average
resolution of 3 to 4 m along the track. Thus a multi-scale analysis from micro-scale events up to the synoptic-scale phenomena
can be presented. All flights and thus all meso- and micro-scale analyses are performed over water only. The obviously very
different characteristics of the cool change structure elements over land are not investigated.
The synoptic analyses for one very typical case show a prefrontal trough as characterized by its position in relation to the
main deep cold front, its source region in Western Australia and its extent to the southeast. Fields of strong wind shear,
temperature gradients, vertical wind and Q-vectors are displayed.
The meso-β-scale x, z-cross-sections derived from two aircraft missions (data of the second one in brackets) show: a shallow cold front with a
160 (60) km wide transition zone in which the near surface potential temperature drops rather steadily by 9 °C (20 °C); a
shallow feeder flow topped by a strong inversion with a vertical gradient of potential temperature up to 5 °C/100 m between
the top of the feeder flow at 400 (200) m and 1500 (700) m; a cross-frontal circulation expressed by the ageostrophic wind
components u
ϕ,subscale and w with a center at 1200 m over the frontal edge of the feeder flow (for one mission only); a strong shear of the along-frontal
wind component v
ϕ with a large increase of the negative v
ϕ-values with height, which very well fits to the synoptic-scale view of the wave structure of the geostrophic wind (well-known
from the upper level synoptic charts) at different heights; a jet core of this along-frontal wind in the center of the cross-frontal
circulation, again for one mission only.
A very striking example of a micro-scale event is an approximately 1 km wide head of a frontal squall line. It shows dramatic
changes of all meteorological parameters. The event is displayed in a horizontal domain of 4 km with full resolution (∼ 4 m).
Derivatives of the measured parameters in the cross-frontal direction add information to the space series of the parameters
themselves. Deformation frontogenesis of potential temperature and specific humidity show very large values on the scale resolved
here. Fortunately the squall line could be sampled again at the same height, but in a somewhat degenerated state 1? h later.
Received September 3, 1999 Revised December 14, 1999 相似文献
20.
Summary ?The analysis of ground-based measurements of solar erythemal ultraviolet (UV) irradiance with a Solar Light 501 biometer,
and total (300–3000 nm) irradiance with an Eppley B&W pyranometer at the Argentine Antarctic Base “Almirante Brown”, Paradise
Bay (64.9° S, 62.9° W, 10 m a.s.l.) is presented. Measurement period extends from February 16 to March 28 2000. A relatively
high mean albedo and a very clean atmosphere characterise the place. Sky conditions were of generally high cloud cover percentage.
Clear-sky irradiance for each day was estimated with model calculations, and the effect of the cloudiness was studied through
the ratio of measured to clear-sky value (r). Two particular cases were analysed: overcast sky without precipitation and overcast sky with rain or slight snowfall, the
last one presenting frequently dense fog. Total irradiance was more attenuated than UV by the homogeneous cloudiness, obtaining
mean r values of 0.54 for erythemal irradiance and 0.30 for total irradiance in the first case (without precipitation) and 0.27
and 0.17 respectively in the second case (with precipitation). Mean r values for the complete period were 0.58 for erythemal irradiance and 0.43 for total irradiance. Erythemal and total daily
insolations reduce quickly at this epoch due to the increase of the noon solar zenith angle and the decrease of daylight time.
Additionally, they were strongly modulated by cloudiness. Measured maxima were 2.71 kJ/m2 and 18.42 MJ/m2 respectively. Measurements were compared with satellite data. TOMS-inferred erythemal daily insolation shows the typical
underestimation with respect to ground measurements at regions of high mean albedo. Measured mean total daily insolation agrees
with climatological satellite data for the months of the campaign.
Received August 9, 2002; revised January 4, 2003; accepted January 28, 2003
Published online May 20, 2003 相似文献