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1.
Summary In order to derive some statistical rainfall characteristics applicable to hydrology, data of continuous rainfall rate recordings of a Jardí gauge installed in Barcelona (Spain) have been converted to an hourly precipitation series. From these data, four useful distributions have been obtained and further compared with some theoretical models. It has been found that the duration of events is distributed exponentially. The duration of rainless intervals follow a generalized Pareto distribution, and the cumulative rainfall in the cumulative rain duration is beta distributed. Concerning the distribution of rain amounts, two models can be accepted, depending on the duration of the events. Comparison with a similar study carried out in Farnborough (United Kingdom) indicates that the events are shorter and that the amounts of rain collected in short events are larger in Barcelona.This work was supported by the DGICYT (Project NAT91-0596) and the CCE (Project PL 910104 Environment).With 7 Figures 相似文献
2.
Climate change,the monsoon,and rice yield in India 总被引：4，自引：1，他引：3
Recent research indicates that monsoon rainfall became less frequent but more intense in India during the latter half of the
Twentieth Century, thus increasing the risk of drought and flood damage to the country’s wet-season (kharif) rice crop. Our statistical analysis of state-level Indian data confirms that drought and extreme rainfall negatively affected
rice yield (harvest per hectare) in predominantly rainfed areas during 1966–2002, with drought having a much greater impact
than extreme rainfall. Using Monte Carlo simulation, we find that yield would have been 1.7% higher on average if monsoon
characteristics, especially drought frequency, had not changed since 1960. Yield would have received an additional boost of
nearly 4% if two other meteorological changes (warmer nights and lower rainfall at the end of the growing season) had not
occurred. In combination, these changes would have increased cumulative harvest during 1966–2002 by an amount equivalent to
about a fifth of the increase caused by improvements in farming technology. Climate change has evidently already negatively
affected India’s hundreds of millions of rice producers and consumers. 相似文献
3.
Summary In this study, spatial interpolation techniques have been applied to develop an objective climatic cartography of precipitation
in the Iberian Peninsula (583,551 km2). The resulting maps have a 200 m spatial resolution and a monthly temporal resolution. Multiple regression, combined with
a residual correction method, has been used to interpolate the observed data collected from the meteorological stations. This
method is attractive as it takes into account geographic information (independent variables) to interpolate the climatic data
(dependent variable). Several models have been developed using different independent variables, applying several interpolation
techniques and grouping the observed data into different subsets (drainage basin models) or into a single set (global model).
Each map is provided with its associated accuracy, which is obtained through a simple regression between independent observed
data and predicted values. This validation has shown that the most accurate results are obtained when using the global model
with multiple regression mixed with the splines interpolation of the residuals. In this optimum case, the average R
2 (mean of all the months) is 0.85. The entire process has been implemented in a GIS (Geographic Information System) which
has greatly facilitated the filtering, querying, mapping and distributing of the final cartography. 相似文献
4.
Numerical Investigations of Mean Winds Within Canopies of Regularly Arrayed Cubical Buildings Under Neutral Stability Conditions 总被引：2，自引：2，他引：0
Recently, several attempts have been made to model the wind velocity in an urban canopy in order to accurately predict the
mixing and transport of momentum, heat, and pollutants within and above the canopy on an urban scale. For this purpose, unverified
assumptions made by Macdonald (Boundary-Layer Meteorol 97:25–45, 2000) to develop a model for the profile of the mean wind
velocity within an urban canopy have been used. In the present study, in order to provide foundations for improving the urban
canopy models, the properties of the spatially-averaged mean quantities used to make these assumptions have been investigated
by performing large-eddy simulations (LES) of the airflow around square and staggered arrays of cubical blocks with the following
plan area densities: λ
p
= 0.05, 0.11, 0.16, 0.20, 0.25, and 0.33. The LES results confirm that the discrepancy between the spatial average of wind
velocity and Macdonald’s five-point average of wind velocity can be large in both types of arrays for large λ
p
. It is also confirmed that Prandtl’s mixing length varies significantly with height within the canopy, contrary to Macdonald’s
assumption for both types of arrays and for both small and large λ
p
. On the other hand, in accordance with Macdonald’s assumption, the sectional drag coefficient is found to be almost constant
with height except in the case of staggered arrays with high λ
p
. 相似文献
5.
D. Gellens 《Theoretical and Applied Climatology》2000,66(1-2):117-129
Summary
k-day extreme precipitation depths (k=1,2,3, … 30) for the climatological network of Belgium (165 stations) are analysed to detect a possible evolution in the
occurrence of extreme rainfall events during the 1951–1995 reference period. The calendar year and the hydrological summer
and winter are considered separately. Spearman’s rank correlation coefficient shows a strong spatial correlation between extreme
k-day precipitation events, depending on the time of the year (lower during summer than during winter) and increasing with
k. In some cases the distances of de-correlation exceed 200 km which is comparable to the size of the country. Due to this
correlation, tests for trends have been carried out on the leading principal components (PC) derived from the covariance matrix.
Various PC selection rules have been applied to identify the number of components to analyse. The number of components needed
to reproduce a given proportion of the total variance varies, with larger values for summer than for winter and a decrease
with growing k. The Fisher test is used as a global test. It combines the individual Mann-Kendall trend tests carried out on the selected
PC scores. Significant trends have been found in extreme winter k-day precipitation for all the values of k and none in extreme summer precipitation. The results for the annual k-day precipitation depths are between those for the two seasons: no trend for small k because summer events dominate and a significant trend for k larger than 7 due to the winter events. Analysis of a few stations with long-term series shows no significant trend for the
period 1910–1995, these series also reproduce almost the same trends as those found for the shorter 1951–1995 period.
Received April 23, 1999 Revised December 6, 1999 相似文献
6.
Summary We investigate whether the rainfall distribution of a drought prone region is characterized by different scaling properties
in comparison to those in temperate regions of the world. We present a Rescaled Range (R/S) analysis of precipitation time
series for 21 stations in northeast Brazil. In order to avoid the inclusion of short term variability, the data were smoothed
by a moving average procedure. Three different algorithms were applied to the data: the empirical procedure proposed by Hurst;
the evaluation of the standard mean deviation around the average profile; the evaluation ofthe mean deviation around the best
fit line. The latter two methods have also been used for the evaluation of the nature of surface irregularities (rugosity)
in surface profiles. The results obtained by the R/S method point to an average value H=0.709 > 0.5. This value indicates that the records show a degree of persistence quite close to that found for 10 stations
in Spain. It also shows that drought occurrence does not alter the persistence of the rainfall distribution.
Received July 13, 1998 Revised January 11, 1999 相似文献
7.
基于闪电低频电场探测阵列（LFEDA）所获得的全闪三维定位数据,研究了2015年8月15日14:30—16:10广州一次雷暴过程中具有明显始发脉冲的闪电初始放电特征及放电规律。结果表明:212例近距离云闪和地闪中,32例闪电由窄偶极性放电事件（NBE）始发,占15%;180例闪电由初始击穿脉冲（定义初始击穿脉冲簇的首个脉冲为FIBP）始发,占85%。作为始发的窄偶极性放电事件（INBE）,其相对孤立且具有较大的相对幅度,INBE与后续闪电的第1个脉冲的时间间隔为7 ms,幅度比为3.5,远大于FIBP相对应的时间间隔0.6 ms和幅度比0.8,INBE后多跟随传统的IBP脉冲。多数正极性INBE与FIBP对应初始向上发展的闪电,而负极性对应初始向下发展的闪电。INBE始发闪电前15 ms的平均发展速度随始发高度的增大而减小,快于FIBP,这与INBE具有更快的速度相关。估计的INBE速度为4.7×107 m·s-1,FIBP速度为1.5×107 m·s-1,两者速度差异也体现在脉冲上升时间方面,INBE具有更快的上升沿。 相似文献
8.
G. Spellman 《Theoretical and Applied Climatology》2000,66(3-4):229-239
Summary A large number of atmospheric circulation classification techniques have been developed in the investigation of synoptic
controls on regional rainfall. Often the rationale is to aid efforts to downscale GCM output for the purpose of producing
more confident climate change impact scenarios. Discrete weather typing techniques, although proven to be successful do not
capture weather type intensity and within-type variability can often be high. In this study an objective indexing method,
developed for Egypt and the British Isles area is applied to the Iberian peninsula. Air flow index values are then used as
predictor variables in simple linear regression models to estimate monthly mean grid point rainfall amounts. Separate models
are evaluated for the winter and summer halves of the year and also for surface and mid-tropospheric flow (500 hPa). The models
are evaluated and compared indicating that the index values provide good estimation of rainfall but variability in performance
between season and site is noted.
Received February 10, 2000 相似文献
9.
Noor Afzal 《Boundary-Layer Meteorology》2009,132(2):241-259
The geostrophic Ekman boundary layer for large Rossby number (Ro) has been investigated by exploring the role played by the mesolayer (intermediate layer) lying between the traditional inner
and outer layers. It is shown that the velocity and Reynolds shear stress components in the inner layer (including the overlap
region) are universal relations, explicitly independent of surface roughness. This universality of predictions has been supported
by observations from experiment, field and direct numerical simulation (DNS) data for fully smooth, transitionally rough and
fully rough surfaces. The maxima of Reynolds shear stresses have been shown to be located in the mesolayer of the Ekman boundary
layer, whose scale corresponds to the inverse square root of the friction Rossby number. The composite wall-wake universal
relations for geostrophic velocity profiles have been proposed, and the two wake functions of the outer layer have been estimated
by an eddy viscosity closure model. The geostrophic drag and cross-isobaric angle predictions yield universal relations, which
are also supported by extensive field, laboratory and DNS data. The proposed predictions for the geostrophic drag and the
cross-isobaric angle compare well with data for Rossby number Ro ≥ 105. The data show low Rossby number effects for Ro < 105 and higher-order effects due to the mesolayer compare well with the data for Ro ≥ 103. 相似文献
10.
Summary For the purpose of providing information to hydrologists for designing costly and large hydraulic structures, estimates of probable maximum precipitation (PMP) for a 2-day duration for stations in the Indian Peninsula lying between 8° N to 20° N were calculated using the Hershfield statistical techniqe. Maximum annual 2-day rainfall data of 80 years from 1901 for 131 stations in the region were used. In order to obtain values of PMP, an enveloping frequency factor (k
m
) curve based on the actual rainfall data of stations in the region was developed. The enveloping curve was then utilised to estimate 2-day PMP values of all the 131 stations. Based on these PMP estimates, a generalised chart showing the spatial distribution of 2-day PMP was prepared. It was found that 2-day PMP estimates over the Indian peninsula varied from 40 to 95 cm and the average ratio of 2-day PMP to the highest observed 2-day rainfall was found to be 1.76.With 2 Figures 相似文献
11.
V. Badescu 《Meteorology and Atmospheric Physics》2001,78(3-4):195-204
Summary
Stationarity of daily averaged surface pressure time series on Mars can be obtained (by differencing) for short time intervals
only. Large pressure variance intervals are usually associated with the dust storm season. Medium and small pressure variance
intervals can be found usually during clear sky periods. General auto-regressive integrated moving average (ARIMA) models
were developed for daily average pressure forecasting at Viking Lander sites. A procedure to find the “appropriate” model
for a given time series was developed. It is based on various degrees of differencing the original time series and a t-statistics-assisted
estimation of the significance of the fitted coefficients. A method employing the cumulative spectrum of the residuals was
used to check the models. ARIMA (3,2,3) seems to be the most “appropriate” model to forecasting the daily average surface
pressure on Mars.
Received December 16, 1999/Revised October 17, 2000 相似文献
12.
Until now, most paleoclimate model-data comparisons have been limited to simple statistical evaluation and simple map comparisons.
We have applied a new method, based on fuzzy logic, to the comparison of 17 model simulations of the mid-Holocene (6 ka BP)
climate with reconstruction of three bioclimatic parameters (mean temperature of the coldest month, MTCO, growing degree-days
above 5 °C, GDD5, precipitation minus evapotranspiration, P−E) from pollen and lake-status data over Europe. With this method, no assumption is made about the distribution of the signal
and on its error, and both the error bars related to data and to model simulations are taken into account. Data are taken
at the drilling sites (not using a gridded interpolation of proxy data) and a varying domain size of comparison enables us
to make the best common resolution between observed and simulated maps. For each parameter and each model, we compute a Hagaman
distance which gives an objective measure of the goodness of fit between model and data. The results show that there is no
systematic order for the three climatic parameters between models. None of the models is able to satisfactorily reproduce
the three pollen-derived data. There is larger dispersion in the results for MTCO and P−E than for GDD5. There is also no systematic relationship between model resolution and the Hagaman distance, except for P−E. The more local character of P−E has little chance to be reproduced by a low resolution model, which can explain the inverse relationship between model resolution
and Hagaman distance. The results also reveal that most of the models are better at predicting 6 ka climate than the modern
climate.
Received: 27 May 1998 / Accepted: 8 January 1999 相似文献
13.
利用NCEP/NCAR再分析和全国740站逐日降水资料,运用一点滞后相关等方法,对2007年夏季江淮流域强降水期间低频振荡的波动活动特征及其与降水低频变化的联系进行了分析。结果表明,在2007年夏季降水中,降水低频分量起着重要作用。降水的低频振荡主周期为10~30d,降水距平时间序列与10~30d低频分量具有较好的对应关系。低频扰动在对流层上层和低层都呈现波列状分布,且在降水活跃位相时,低频环流在高、低层具有斜压结构。在对流层上层,低频扰动有缓慢的东移倾向,相速度为每天2~3个经度。西风带中存在多次移动性波列向下游的传播,且在120°E以西以每天14经度的群速度向下游频散能量,表明10~30d低频波动具有明显的下游发展特征。在强降水开始5d前,低频波动与能量可起源于高纬的乌拉尔山附近,沿着西北-东南向的路径向下游传播。下游发展的低频波动为江淮流域带来了能量,为强降水的发生提供了条件。这些结果加深了人们对低频波动在江淮流域强降水过程中所起作用的认识,可为寻找江淮流域强降水过程预报线索提供科学依据。 相似文献
14.
M. N. Khaliq P. Gachon A. St-Hilaire T. B. M. J. Ouarda B. Bobée 《Theoretical and Applied Climatology》2007,88(1-2):83-101
Summary Summer-season (May–September) daily maximum temperature (T
max) and daily minimum temperature (T
min) observations and three types of heat spells obtained from these temperature observations at seven weather stations located
in southern Quebec (Canada) for the 60-year period from 1941 to 2000 are studied to assess temporal changes in their characteristics
(i.e. frequency of occurrence, seasonal hot days and extremal durations of heat spells). Type-A and Type-B heat spells are
obtained respectively from T
max and T
min observations and Type-C heat spells from simultaneous joint observations of T
max and T
min using suitable thresholds and spells of duration ≥1-day and ≥3-day. The results of this investigation show that the majority
of the selected percentiles (i.e. 5P, 10P, 25P, 50P, 75P, 80P, 90P, 92P, 95P, and 98P) of T
max observations show a negative time-trend with statistically significant decreases (at 10% level) in some of the higher percentiles
and in the maximal values at four out of seven stations. Almost all of the selected percentiles (same as for the T
max) and the maximal and minimal values of T
min observations show a positive trend, with statistically significant increases for all seven stations. Examination of frequencies
of occurrence of heat spells, seasonal hot days and annual extremes of heat spell durations indicate that many of these characteristics
of heat spells have undergone statistically significant changes over time at some of the stations for Type-A and Type-B heat
spells as compared to Type-C heat spells. The Type-C heat spells are generally small in number and are found to be relatively
temporally stable. More severe Type-C heat spells, i.e. the ones having T
max and T
min values simultaneously above very high thresholds and with duration ≥3-day have been rarely observed in southern Quebec. 相似文献
15.
This paper compares the performance of seven disaggregation models, based on various approaches and/or concepts, for the generation of 10-min time step rainfall series from hourly rainfall series. The so-called constant disaggregation model and a linear model based on the external temporal pattern of rainfall are first considered. The other models are stochastic: the first ones are based on a given probability density function applying for the 10-min rainfall amounts of the hour to disaggregate. This probability density function is either uniform or derived from the external temporal pattern of rainfall. The other stochastic models are scaling models using canonical or microcanonical multiplicative random cascades. The comparison of the models is based on their ability to reproduce some important statistical characteristics of the observed time series: variance, skewness coefficient, wet/dry properties of 10-min rainfall amounts; rainfall amounts quantiles for different return periods; autocorrelation of 10-min rainfall amounts. A continuous hydrological simulation is next applied to produce for each generated rainfall series a continuous discharge series used afterwards for a retention design. The ability of the different disaggregation models to produce rainfall time series resulting in the same retention design than the one obtained with the observed rainfall series is finally analysed. Deterministic models as well as simpler stochastic models have rather bad performances when compared to the others. Because it is non-conservative, the model based on a microcanonical random cascade performs also very poorly. It significantly overestimates all studied statistics. Models based on microcanonical random cascades achieve the best performance. They perform reasonably well for the reproduction of rainfall statistics and almost perfectly for the reproduction of runoff and storage design variables. Results finally highlight the interest of including in the disaggregation scheme information related to the external temporal pattern of rainfall. 相似文献
16.
Summary In a previous study the authors have estimated the probable maximum precipitation (PMP) for a 2-day duration using Hershfield's formulaX
PMP =X
n
+k
m
n
for stations in the southern Indian region. In this paper, the study is extended to estimate the PMP for stations in the north Indian region, north of 20°N. Maximum annual 2-day rainfall data for an 80-year period, from 1901, were obtained for 286 stations in the region. A mathematical relationship between the frequency factor (k
m
) and the mean annual extreme rainfall (X
n
) was developed to bek
m
= 18.15 exp (–0.0448X
n
). This equation was used to obtaink
m
for different values ofX
n
and, subsequently, to estimate 2-day PMP values for the 286 stations. Using these PMP estimates, a generalised chart was prepared, showing the spatial distribution of 2-day PMP. It was found that 2-day PMP over the north Indian region varied from 60 cm to 130 cm, and the average ratio of the 2-day PMP to the highest observed 2-day rainfall was found to be 1.91. The results show that there have been instances when almost 2-day point PMP have occurred at some of the stations in the region. These results indicate that the statistically estimated PMP rainall are not therefore, mere theoretical estimates, but they can occur under optimum meteorological conditions.With 4 Figures 相似文献
17.
F. D’Andrea S. Tibaldi M. Blackburn G. Boer M. Déqué M. R. Dix B. Dugas L. Ferranti T. Iwasaki A. Kitoh V. Pope D. Randall E. Roeckner D. Strauss W. Stern H. Van den Dool D. Williamson 《Climate Dynamics》1998,14(6):385-407
As a part of the Atmospheric Model Intercomparison Project (AMIP), the behaviour of 15 general circulation models has been
analysed in order to diagnose and compare the ability of the different models in simulating Northern Hemisphere midlatitude
atmospheric blocking. In accordance with the established AMIP procedure, the 10-year model integrations were performed using
prescribed, time-evolving monthly mean observed SSTs spanning the period January 1979–December 1988. Atmospheric observational
data (ECMWF analyses) over the same period have been also used to verify the models results. The models involved in this comparison
represent a wide spectrum of model complexity, with different horizontal and vertical resolution, numerical techniques and
physical parametrizations, and exhibit large differences in blocking behaviour. Nevertheless, a few common features can be
found, such as the general tendency to underestimate both blocking frequency and the average duration of blocks. The problem
of the possible relationship between model blocking and model systematic errors has also been assessed, although without resorting
to ad-hoc numerical experimentation it is impossible to relate with certainty particular model deficiencies in representing
blocking to precise parts of the model formulation.
Received: 16 July 1997/Accepted: 20 October 1997 相似文献
18.
A parametrization of the lateral waterflow for the global scale 总被引：1，自引：2，他引：1
The representation of hydrological land surface processes has, so far, been treated inadequately in global models of the
atmospheric general circulation (GCMs). In particular the lateral waterflows from the continents into the ocean have been
described unsatisfactorily. The aim of this study is to develop a model for the lateral waterflow on the global scale which
describes the translation and retention of the lateral discharge as a function of the spatially distributed land surface characteristics
that are globally available. Here, global scale refers to the resolution of 0.5° and smaller, corresponding to a typical GCM
gridbox area of about 2500 km2. Discharge models need a number of specific input variables that are usually not available from measurements such as runoff
and drainage. Therefore, these variables have to be derived from observed data such as precipitation and surface air temperature.
For the model development in this study, a new simplified land surface scheme was applied to compute these variables. The
discharge from a catchment of approximately the size of a 0.5° gridbox was simulated using several types of models. The intercomparison
of the simulated lateral flows of the different models shows that as a minimum a separation between flow processes such as
overland flow, baseflow and riverflow is required to yield good discharge simulations. As both the retention and translation
of a flow process need to be simulated, a two-parameter model is required for the representation of overland flow and riverflow.
For the baseflow, a one-parameter model is sufficient. The resulting model structure is called the hydrological discharge model or HD model. A first parametrization approach was defined using the gridbox characteristics of topography gradient and gridbox length.
The skill of the discharge simulation depends not only on the formulations of the model, but also on the precise definition
of the boundaries of the model catchments. The sizes and the positioning of the model catchments on the globe were defined
by using a river direction file as well as a modified topography dataset. In a first application, the HD model successfully
simulated river discharge using runoff and drainage from a five year atmospheric GCM integration (ECHAM4-T42) as input. The
annual cycles of the monthly means of the simulated discharge of several large rivers were compared to the observed discharges
provided by the Global Runoff Data Centre. The HD model achieves a considerable improvement of the simulated discharge compared
to the model which is currently operational at MPI. The improved volume of the discharge is directly related to the definition
of more realistic model catchments and the improved timing of the flow is mainly due to the newly introduced separation of
the flow processes.
Received: 20 November 1996 / Accepted: 8 July 1997 相似文献
19.
An increase in global average precipitation of about 10% is simulated by two global climate models with mixed layer oceans
in response to an equilibrium doubling of carbon dioxide. The UKHI model was developed in the United Kingdom at the Hadley
Centre for Climate Prediction and Research and the CSIRO9 model was developed in Australia by the CSIRO Division of Atmospheric
Research. Regional changes in daily precipitation simulated by these models have been compared. Both models simulate fewer
wet days in middle latitudes, and more wet days in high latitudes. At middle and low latitudes, there is a shift in the precipitation
type toward more intense convective events, and fewer moderate non-convective events. At high latitudes, the precipitation
type remains non-convective and all events simply get heavier, resulting in fewer light events and more moderate and heavy
events. The probability of heavy daily precipitation increases by more than 50% in many locations. Extreme events with a probability
of 1% or less were considered in terms of return periods (the average period between events of the same magnitude). For a
given return period of at least 1 y, precipitation intensity in Europe, USA, Australia and India increases by 10 to 25%. For
a given precipitation intensity, the average return period becomes shorter by a factor of 2 to 5. Given that larger changes
in frequency occur for heavier simulated events, changes may be even greater for more-extreme events not resolved by models.
Received: 1 July 1996 / Accepted: 21 March 1997 相似文献
20.
Summary Cloud parameters and surface radiative fluxes predicted by regional atmospheric models are directly compared with observations
for a 10-day period in late summer 1995 characterized by predominantly large-scale synoptic conditions. Observations of total
cloud cover and vertical cloud structure are inferred from measurements with a ground-based network of Lidar ceilometers and
IR-radiometers and from satellite observations on a 100 kilometer scale. Ground-based observations show that at altitudes
below 3 km, implying liquid water clouds, there is a considerable portion of optically non-opaque clouds. Vertical distributions
of cloud temperatures simultaneously inferred from the ground-based infrared radiometer network and from satellite can only
be reconciled if the occurrence of optically thin cloud structures at mid- and high tropospheric levels is assumed to be frequent.
Results of three regional atmospheric models, i.e. the GKSS-REMO, SMHI-HIRLAM, and KNMI-RACMO, are quantitatively compared
with the observations. The main finding is that all models predict too much cloud amount at low altitude below 900 hPa, which
is then compensated by an underestimation of cloud amount around 800 hPa. This is likely to be related with the finding that
all models tend to underestimate the planetary boundary layer height. All models overpredict the high-level cloud amount albeit
it is difficult to quantify to what extent due to the frequent presence of optically thin clouds. Whereas reasonably alike
in cloud parameters, the models differ considerably in radiative fluxes. One model links a well matching incoming solar radiation
to a radiatively transparent atmosphere over a too cool surface, another model underpredicts incoming solar radiation at the
surface due to a too strong cloud feedback to radiation, the last model represents all surface radiative fluxes quite well
on average, but underestimates the sensitivity of atmospheric transmissivity to cloud amount.
Received August 31, 2000 Revised March 15, 2001 相似文献