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1.
This study presents the monthly climatology and variability of the historical soviet snow depth data. This data set was developed
under the bilateral data exchange agreement between United States of America and the former Union of Soviet Socialist Republics.
The original data is for 284 stations for periods varying from 1881 upto 1985. The seasonal cycle of the mean snow depth has
been presented both as spatial maps and as averages over key locations. The deepest snow (=80 cms/day) areas are found over
Siberia (in Particular over 80′–100 ′E, 55′–70 ′N) during March. Over the course of the annual cycle average snow depth over
this region changes dramatically from about 10 cms in October to about 80 cms in March. The variability is presented in the
form of spatial maps of standard deviation. To investigate the interaction of snow depth with Indian monsoon rainfall (IMR),
lag and lead correlation coefficients are computed. Results reveal that the winter-time snow depth over western Eurasia surrounding
Moscow (eastern Eurasia in central Siberia) shows significant negative (positive) relationship with subsequent IMR. Following
the monsoon the signs of relationship reverse over both the regions. This correlation structure is indicative of a midlatitude
longwave pattern with an anomalous ridge (trough) over Asia during the winter prior to a strong (weak) monsoon. As the time
progresses from winter to spring, the coherent areas of significant relationship show southeastward propagation. Empirical
orthogonal function analysis of the snow depth reveal that the first mode describes a dipole-type structure with one centre
around Moscow and the other over central Siberia, depicting similar pattern as the spatial correlation structure. The decadal-scale
IMR variations seem to be more associated with the Northern Hemisphere midlatitude snow depth variations rather than with
the tropical ENSO (El Nino Southern Oscillation) variability.
Received: 16 March 1998 / Accepted: 24 December 1998 相似文献
2.
In order to estimate the impacts of buildings on air pollution dispersion, numerical simulations are performed over an idealized
urban area, modelled as regular rows of large rectangular obstacles. The simulations are evaluated with the results of the
Mock Urban Setting Test (MUST), which is a near full-scale experiment conducted in Utah’s West Desert area: it consists of
releases of a neutral gas in a field of regularly spaced shipping containers. The numerical simulations are performed with
the model Mercure_Saturne, which is a three-dimensional computational fluid dynamics code adapted to atmospheric flow and dispersion simulations. It
resolves complex geometries and uses, in this study, a k–∈ closure for the turbulence model. Sensitivity studies focus on how to prescribe the inflow conditions for turbulent kinetic
energy. Furthermore, different sets of coefficients available in the literature for the k–∈ closure model are tested. Twenty MUST trials with different meteorological conditions are simulated and detailed analyses
are performed for both the dynamical variables and average concentration. Our results show overall good agreement according
to statistical comparison parameters, with a fraction of predictions for average concentration within a factor of two of observations
of 67.1%. The set of simulations offers several inflow wind directions and allows us to emphasize the impact of elongated
buildings, which create a deflection of the plume centerline relative to the upstream wind direction. 相似文献
3.
Li Chongyin 《大气科学进展》1998,15(1):31-40
The data analyses found at first that the air—sea system in the northwestern Pacific region has clear systematical quasi—decadal
oscillation, such as the surface air temperature, the subtropical high activities over the northwestern Pacific and the SSTA
which has different time-scale features from the temporal variation with 3–4 years period of SSTA in the equatorial Pacific.
In East Asia, the climate variations, such as the surface air temperature, the precipitation and the beginning date of Mei-yu
in the Yangtze River basin, also have clear quasi-decadal oscillation. They can be regarded as the influences of quasi-decadal
oscillation of air-sea system in the northwestern Pacific region.
This research was supported by the Chinese Academy of Sciences and ‘95’ National Project- “Short-Range Climate Production
System”. 相似文献
4.
The 30–60 day oscillation is an important aspect of the atmospheric variance in the tropical area. A number of works have
been done on this phenomenon, this article is a further one. A quasi-geostrophic linear model that consists of a two-layer
free atmosphere and a well-mixed boundary layer is used to investigate the instability of intraseasonal oscillation, its propagation
and vertical structures. Results show that the dynamical coupling and interaction between the barotropic and baroclinic components
via boundary layer convergence / divergence are responsible for the appearance of a new kind of low-frequency wave. Such wave
is very different from the traditional tropical Rossby wave. It can propagate westward and eastward. Some behaviours of it
appear to resemble the observed 30–60 day oscillation mode in many aspects, such.as vertical structures, zonal and meridional
propagations. Now many researchers emphasize the direct relationship between CISK-Kelvin mode and the tropical atmospheric
30–60 oscillation. It is considered that CISK-Rossby mode should not be neglected. 相似文献
5.
Projected changes in summer precipitation characteristics in China during the 21st century are assessed using the monthly precipitation outputs of the ensemble of three “best” models under the Special Report on Emissions Scenarios (SRES) A1B, A2, and B1 scenarios. The excellent reproducibility of the models both in spatial and temporal patterns for the precipitation in China makes the projected summer precipitation change more believable for the future 100 years. All the three scenarios experiments indicate a consistent enhancement of summer precipitation in China in the 21st century. However, the projected summer precipitation in China demonstrates large variability between sub-regions. The projected increase in precipitation in South China is significant and persistent, as well as in North China. Meanwhile, in the early period of the 21st century, the region of Northeast China is projected to be much drier than the present. But, this situation changes and the precipitation intensifies later, with a precipitation anomaly increase of 12.4%–20.4%
at the end of the 21st century. The region of the Xinjiang Province probably undergoes a drying trend in the future 100 years, and is projected to decrease by 1.7%–3.6% at the end of the 21st century. There is no significant long-term change of the projected summer precipitation in the lower reaches of the Yangtze River valley. A high level of agreement of the ensemble of the regional precipitation change in some parts of China is found across scenarios but smaller changes are projected for the B1 scenario and slightly larger changes for the A2 scenario. 相似文献
6.
We derive a conceptual model of the flow over heterogeneous terrain consisting of patches with contrasting Bowen ratios. Upward
moving eddies are assumed to carry heterogeneous properties, whereas downward moving eddies carry homogeneous properties.
This results in a decorrelation of temperature and humidity as the contrast between the patches increases. We show that this
model is able to reproduce the relationship developed by Lamaud and Irvine (Boundary-Layer Meteorol. 120:87–109, 2006). Some
details differ from their expression but are in accordance with data obtained over African savannah. We extend the conceptual
model to a combination of any scalars, not necessarily linked through the surface energy balance (as is the case for temperature
and humidity). To this end we introduce a new parameter that describes the surface heterogeneity in surface fluxes. The results
of the current model can be used to predict the discrepancy between similarity relationships for different scalars over heterogeneous
terrain. 相似文献
7.
R. A. Hill K. Smith K. Russell T. Misselbrook S. Brookman 《Journal of Atmospheric Chemistry》2008,59(2):83-98
Ammonia emissions from stored farm manures form a small but significant proportion (∼10%) of the total emitted annually from
UK sources. These emissions are regulated by factors including: the surface area of the store; the storage method; the physical
form of the stored manure and the source of manure. A method was developed to estimate in situ emissions from a range of store
types (weeping wall and earth-banked lagoon) that are currently under-represented in UK emissions estimates. Passive diffusion
samplers (Willems Badges) were used to determine vertical concentration profiles to a height of 4.5 m at a number of locations
around each slurry store. An atmospheric dispersion model was applied to estimate the contribution from emissions from other
on-farm ammonia sources to the measured data and also to determine the emission rates from the stored manure. A procedure
was applied whereby the emission rates from each source were allowed to vary and a numerical equation solver was applied to
backfit the modelled data set to the field measurements. Measurements were collected at four farms on a monthly basis throughout
the year, with each dataset being collected over 24 h. The uncertainties in the estimates of emissions from the slurry stores
during individual measurement periods typically ranged between 20–40% though higher uncertainties occurred when emission fluxes
from the stores were below 0.25 g NH3–N m−2 day−1 and were entrained in the wakes, and mixed with the emissions, of adjacent buildings. The average emission from the farms
was 0.6 g NH3–N m−2 day−1 which agrees with other recent data on ammonia emissions from crusted slurry stores and, though it is within the range of
data considered in the UK emissions inventory, suggests that emissions from weeping wall stores and earth-banked lagoons may
be currently overestimated in national predictions. 相似文献
8.
Variation of the Sectional Drag Coefficient of a Group of Buildings with Packing Density 总被引:2,自引:2,他引:0
Reynolds-averaged Navier–Stokes (RANS) simulations of turbulent flow over groups of buildings with different packing densities
are reported. The results for a selected packing density are compared with direct numerical simulations (DNS) previously validated
against wind-tunnel data. The present study is focused on average properties of the flow, especially on the drag coefficients,
and is a first attempt to provide information on these parameters (their values are not generally known) for a range of packing
densities, for a given staggered arrangement of cubes using RANS methods. However, some of the limitations of RANS have come
to light. Hence, it is recommended that such simulations are ‘calibrated’ against experimental or DNS data, as is done here. 相似文献
9.
The daily outgoing longwave radiation (OLR) field in boreal summer shows significant power spectrum peaks on quasi-biweekly (10–20-day) and intraseasonal (20-80-day) timescales over the Indo-western Pacific warm pool, especially over the South China Sea and Bay of Bengal. The quasi-biweekly oscillation (QBWO) originates from off-equatorial western North Pacific, and is characterized by a northwest-southeast oriented wave train pattern, propagating northwestward. The intraseasonal oscillation (ISO), on the other hand, originates from the equatorial Indian Ocean and propagates eastward and northward. Why the equatorial mode possesses a 20–80-day periodicity while the off-equatorial mode favors a 10–20-day periodicity is investigated through idealized numerical experiments with a 2.5-layer atmospheric model. In the off-equatorial region, the model simulates, under a realistic three-dimensional summer mean flow, the most unstable mode that has a wave train pattern with a typical zonal wavelength of 6000 km and a period of 10–20 days, propagating northwestward. This is in contrast to the equatorial region, where a Madden-Julian oscillation (MJO) like mode with a planetary (wavenumber-1) zonal scale and a period ranging from 20 to 80 days is simulated. Sensitivity experiments with different initial conditions indicate that the QBWO is an intrinsic mode of the atmosphere in boreal summer in the off-equatorial Indo-western Pacific region under the summer mean state, while the MJO is the most unstable mode in the equatorial region. 相似文献
10.
The inter-basin teleconnection between the North Atlantic and the North Pacific ocean–atmosphere interaction is studied using
a coupled ocean–atmosphere general circulation model. In the model, an idealized oceanic temperature anomaly is initiated
over the Kuroshio and the Gulf Stream extension region to track the coupled evolution of ocean and atmosphere interaction,
respectively. The experiments explicitly demonstrate that both the North Pacific and the North Atlantic ocean–atmosphere interactions
are intimately coupled through an inter-basin atmospheric teleconnection. This fast inter-basin communication can transmit
oceanic variability between the North Atlantic and the North Pacific through local ocean-to-atmosphere feedbacks. The leading
mode of the extratropical atmospheric internal variability plays a dominant role in shaping the hemispheric-scale response
forced by oceanic variability over the North Atlantic and Pacific. Modeling results also suggest that a century (two centuries)
long observations are necessary for the detection of Pacific response to Atlantic forcings (Atlantic response to Pacific forcing). 相似文献
11.
Intercomparison of Planetary Boundary-Layer Parametrizations in the WRF Model for a Single Day from CASES-99 总被引:11,自引:6,他引:5
This study compares five planetary boundary-layer (PBL) parametrizations in the Weather Research and Forecasting (WRF) numerical
model for a single day from the Cooperative Atmosphere-Surface Exchange Study (CASES-99) field program. The five schemes include
two first-order closure schemes—the Yonsei University (YSU) PBL and Asymmetric Convective Model version 2 (ACM2), and three
turbulent kinetic energy (TKE) closure schemes—the Mellor–Yamada–Janjić (MYJ), quasi-normal scale elimination (QNSE), and
Bougeault–Lacarrére (BouLac) PBL. The comparison results reveal that discrepancies among thermodynamic surface variables from
different schemes are large at daytime, while the variables converge at nighttime with large deviations from those observed.
On the other hand, wind components are more divergent at nighttime with significant biases. Regarding PBL structures, a non-local
scheme with the entrainment flux proportional to the surface flux is favourable in unstable conditions. In stable conditions,
the local TKE closure schemes show better performance. The sensitivity of simulated variables to surface-layer parametrizations
is also investigated to assess relative contributions of the surface-layer parametrizations to typical features of each PBL
scheme. In the surface layer, temperature and moisture are more strongly influenced by surface-layer formulations than by
PBL mixing algorithms in both convective and stable regimes, while wind speed depends on vertical diffusion formulations in
the convective regime. Regarding PBL structures, surface-layer formulations only contribute to near-surface variability and
then PBL mean properties, whereas shapes of the profiles are determined by PBL mixing algorithms. 相似文献
12.
B. W. Buckley L. M. Leslie M. Leplastrier L. Qi 《Meteorology and Atmospheric Physics》2007,97(1-4):69-91
Summary There are three main aims of this study. First, the main features of the active 2005–2006 Australian region tropical cyclone
(TC) season are summarized, with particular emphasis on the northwest Australian region. Second, an assessment is made of
the skill of the available operational global and regional numerical weather prediction (NWP) models for three of the most
significant TCs (TCs Clare, Glenda and Hubert), each of which made landfall on the northwest coast of Australia. Third, high-resolution
numerical modelling simulations of these same three TCs are described in detail. The numerical weather prediction (NWP) model
used here was developed at the University of Oklahoma, and in this study it utilises initial and boundary conditions obtained
from archived analyses and forecasts provided by the Australian Bureau of Meteorology, as well as a 4D-Var data assimilation
scheme to ingest all available satellite data. The high-resolution numerical model is multiply two-way nested, with the innermost
domain having a resolution of 5 km. It was found that unlike the operational models, which were restricted by relatively low
resolution and less data, the high resolution model was able to capture most of the major features of all three TC lifecycles
including development from initial tropical depressions, intensification, and their tracks, landfall, and associated rainfall
and wind fields. 相似文献
13.
In the context of 1905-1995 series from Nanjing and Hangzhou, study is undertaken of establishing a predictive model of annual mean temperature in 1996-2005 to come over the Changjiang (Yangtze River) delta region through mean generating function and artificial neural network in combination. Results show that the established model yields mean error of 0.45℃ for their absolute values of annual mean temperature from 10 yearly independent samples (1986-1995) and the difference between the mean predictions and related measurements is 0.156℃. The developed model is found superior to a mean generating function regression model both in historical data fitting and independent sample prediction. 相似文献
14.
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
15.
D. Narayana Rao H. R. Singh J. R. Kulkarni A. Y. Chandrika S. Vijaya Bhaskara Rao 《Meteorology and Atmospheric Physics》2000,73(1-2):55-59
Summary Mesosphere-Stratosphere-Troposphere (MST) Radar wind data for the period June through September 1996 have been examined to
study vertical variation of Madden-Jullian Oscillations in wind and eddy kinetic energy (eke) in the normal monsoon season.
The domain of analysis in the vertical is from 6 to 20 km with a height resolution of 150 m. Fast-Fourier-Transformation (FFT)
has been applied to zonal (u), meridional(v) components of wind to extract the Madden-Jullian oscillations and eke. There
are three dominant modes viz., 50–70, 30–40 and 10–20 day periodicity, which contain considerable fraction of energy and show
high degree of vertical variability. The peak amplitude of 50–70 day mode in u, 30–40 mode in v and eke were observed at 16–17 km
just below the tropopause level. The peak amplitudes of 30–40 day mode in u and 50–70 day mode in v were found in the height
region of 13–16 km. To understand the origin and propagation of these waves, wave energy is calculated. The wave energy is
higher at tropospheric heights than at lower stratospheric heights indicating that the origin of these waves is in the troposphere,
and a part of the energy leaks into the stratosphere.
Received September 17, 1998/Revised September 26, 1999 相似文献
16.
Aaron Anthony Boone Isabelle Poccard-Leclercq Yongkang Xue Jinming Feng Patricia de Rosnay 《Climate Dynamics》2010,35(1):127-142
The West African monsoon (WAM) circulation and intensity have been shown to be influenced by the land surface in numerous
numerical studies using regional scale and global scale atmospheric climate models (RCMs and GCMs, respectively) over the
last several decades. The atmosphere–land surface interactions are modulated by the magnitude of the north–south gradient
of the low level moist static energy, which is highly correlated with the steep latitudinal gradients of the vegetation characteristics
and coverage, land use, and soil properties over this zone. The African Multidisciplinary Monsoon Analysis (AMMA) has organised
comprehensive activities in data collection and modelling to further investigate the significance land–atmosphere feedbacks.
Surface energy fluxes simulated by an ensemble of land surface models from AMMA Land-surface Model Intercomparison Project
(ALMIP) have been used as a proxy for the best estimate of the “real world” values in order to evaluate GCM and RCM simulations
under the auspices of the West African Monsoon Modelling Experiment (WAMME) project, since such large-scale observations do
not exist. The ALMIP models have been forced in off-line mode using forcing based on a mixture of satellite, observational,
and numerical weather prediction data. The ALMIP models were found to agree well over the region where land–atmosphere coupling
is deemed to be most important (notably the Sahel), with a high signal to noise ratio (generally from 0.7 to 0.9) in the ensemble
and a inter-model coefficient of variation between 5 and 15%. Most of the WAMME models simulated spatially averaged net radiation
values over West Africa which were consistent with the ALMIP estimates, however, the partitioning of this energy between sensible
and latent heat fluxes was significantly different: WAMME models tended to simulate larger (by nearly a factor of two) monthly
latent heat fluxes than ALMIP. This results due to a positive precipitation bias in the WAMME models and a northward displacement
of the monsoon in most of the GCMs and RCMs. Another key feature not found in the WAMME models is peak seasonal latent heat
fluxes during the monsoon retreat (approximately a month after the peak precipitation rates) from soil water stores. This
is likely related to the WAMME northward bias of the latent heat flux gradient during the WAM onset. 相似文献
17.
Evaporation from heterogeneous and sparse canopies is often represented by multi-source models that take the form of electrical
analogues based upon resistance networks. The chosen representation de facto imposes a specific form on the composition of
elementary fluxes and resistances. The two- and three-source representations are discussed in relation to previous work where
some ambiguities arise. Using the two-layer model (Shuttleworth and Wallace, Q J R Meteorol Soc 111:839–855, 1985) and the clumped (three-source) model (Brenner and Incoll, Agric For Meteorol 84:187–205, 1997) as a basis, it is shown that the stomatal characteristics of the foliage (amphistomatous or hypostomatous) generate different
formulations. New generic and more concise equations, valid in both configurations, are derived. The differences between the
patch and layer approaches are outlined and the consequences they have on the composition and formulation of component fluxes
are specified. Then, the issue of calculating the effective resistances of the single-layer model from multi-source representations
is addressed. Finally, a sensitivity analysis is carried out to illustrate the significance of the new formulations. 相似文献
18.
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
19.
20.
O. A. Anisimov I. I. Borzenkova E. L. Zhil’tsova O. K. Zakharova V. A. Kokorev S. A. Reneva Yu. G. Strel’chenko 《Russian Meteorology and Hydrology》2011,36(5):307-314
The maps are presented of seasonal air temperature and precipitation amount anomalies averaged for the whole Volga region
and adjacent territory for two time periods, 1946–1977 and 1978–2008. It is demonstrated that the considerable differences
in the thermal and moistening regimes of the Volga region exist for these two periods. The relation is described between the
variations of temperature and precipitation amount and the circulation types according to Vangengeim-Girs classification as
well as the possibility to use these data for specifying the climatic scenarios obtained on the basis of physically complete
hydrodynamic models. 相似文献