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1.
C. Serra A. Burgueño M. D. Martínez X. Lana 《Theoretical and Applied Climatology》2006,85(3-4):165-183
Summary A spatiotemporal trend analysis of different magnitudes related to the number and length of the dry spells in Catalonia (NE
Spain) has been conducted based on daily rainfall records taken from 40 rain gauges during the second half of the 20th century. Dry spells have been computed for threshold levels of 0.1, 1, 5 and 10 mm/day at annual and semi-annual scales.
The winter half-year is defined from October to March and the summer half-year from April to September. The magnitudes considered
are the number, the maximum length and the mean length of the dry spells for every year and half-year. The spatial patterns
of the average values of these magnitudes at the annual scale show a greater similarity with those of the summer half-year
than with those of the winter half-year. A S–N or SW–NE gradient of the number of dry spells appears during the summer half-year
for every threshold level. Trends of the analysed magnitudes are derived from linear regression and local statistical significances
at the 95% confidence level are established using the Mann-Kendall test. Field significant trends are investigated by means
of Monte Carlo simulations. The most relevant finding is that the number of dry spells per year depicts significant trends
for the annual and winter-half series, with an overall decreasing trend for 5 and 10 mm/day thresholds. These observed trends
are in agreement with changes in North Atlantic cyclone tracks and in Mediterranean Low dynamics, due to increasing greenhouse
gas concentrations. 相似文献
2.
Spatial and temporal analysis of dry spells in Croatia 总被引：3，自引：1，他引：2
Systematic statistical analysis of dry day sequences, which are defined according to 0.1, 1, 5 and 10 mm of precipitation-per-day thresholds, is performed on seasonal and yearly basis. The data analysed come from 25 Croatian meteorological stations and cover the period 1961–2000. Climatological features of the mean and maximum dry spell durations, as well as the frequency of long dry spells (>20 days) are discussed. The results affirm the three main climatological regions in Croatia, with the highlands exhibiting shorter dry spells than the mainland, and the coastal region exhibiting longer dry spells. The prevailing positive trend of both mean and maximal durations is detected during winter and spring seasons, while negative trend dominate in autumn for all thresholds. Positive field significant trends of mean dry spell duration with 5 and 10 mm thresholds are found during spring and the same is valid for annual maximum dry spell duration with a 10 mm threshold. It is found that the Discrete Autoregressive Moving Average (DARMA(1,1)) model can be used to estimate the probabilities of dry spells in Croatia that are up to 20–30 days long. 相似文献
3.
Demarcating the worldwide monsoon 总被引：10，自引：1，他引：10
Summary The monsoon is a global climate phenomenon. This paper addresses the seasonal reversal of atmospheric circulation and the
transition of dry/wet spells in the monsoon regions worldwide. The NCEP/NCAR 850 hPa wind reanalysis data for 1950–1999 and
the upper-tropospheric water vapour (UTWV) band brightness temperature (BT) data observed by NOAA polar orbiting satellites
for 1980–1995 are used. In the tropics, there are three large wet-UTWV centres. The summer monsoon in the subtropics can be
defined as the expansion of these centres associated with the influence of cross-equatorial flows. Specifically, the dry/wet
spell transition is determined by the BT values that are smaller than 244 K. The regions of the South and North African monsoons,
the Asian-northwest Pacific and Australian-Southwest Pacific monsoons, and the North and South American monsoons are examined
with a focus on the dry/wet spell transition and stream field features.
Findings suggest that the summer monsoons over many subtropical regions can be defined by both cross-equatorial flows and
dry/wet spell transitions. In the mid- and low-latitudes, there exist six major dry/wet spell transition regions with a dry
or wet period lasting more than one month. The region of most significant change is located over the subtropical North Africa–Asia–northwest
Pacific. The others appear over subtropical South Africa, Indonesia–Australia, southwest Pacific, the Mexico-Caribbean Sea,
and subtropical South America. In addition, three regions exist where only one of the two indicators (cross-equatorial flow
and dry/wet transition) is satisfied. The first is near the Equator where the directions of cross-equatorial flows alternate
but a dry/wet spell transition is never experienced. The second is over North Africa where only the dry/wet spell transition
can be found but not the cross-equatorial flows. The third is over the mid-latitude regions in North China, South Africa,
and northern North America. These regions are influenced by cross-equatorial flows but the upper-tropospheric water vapour
content is not as high as that in tropical regions.
Received June 29, 2000 Revised May 15, 2001 相似文献
4.
Summary In the present study the trends in frequency and duration of dry spells in six sub-regions of China were analyzed for the summer-half-year season (April–September) in period 1956–2000. A dry spell was defined as a number of consecutive days without measurable precipitation. For the frequency of short dry spells (length <10 days), significant changes are observed in the North, Northeast and Southwest China. For the frequency of long dry spells (length 10 days) there are significant trends in North and Northeast China; while no remarkable trends in frequency are found in other regions. There are also significant lengthening trends in dry spell duration in North and Northeast China, resulting mainly from the long-term changes in short dry spells. No significant change is observed for the maximum length in all regions. It is found that the temporal distribution of precipitation within the rainy season would notably impact the features of dry spells. An increase in the precipitation amount does not necessarily mean a synchronous reduction in dry spell frequency and/or duration. Seasonal mean anomalies of 500hPa heights in association with the long dry spells show similar spatial patterns over the middle to high latitudes for five of the six sub-regions (with exception of the case of Southwest China), resembling a west–east direction dipole in latitudes about 30°N northwards. For the case of Southwest China the dominant feature in 500hPa heights is the negative anomalies over most middle to high latitude Asia. Among these cases there are recognizable differences, particularly, in the tropical regions in western Pacific. That would provide useful information of circulation background for understanding the climate extremes. 相似文献
5.
Summary This paper assesses recent changes in extremes of seasonal rainfall in Ethiopia based on daily rainfall data for 11 key stations
over the period 1965–2002. The seasons considered are Kiremt (‘main rains’, June–September) and Belg (‘small rains’, February/March–May). The Mann-Kendall and linear regression trend tests show decreasing trends in the Kiremt and the Belg extreme intensity and maximum consecutive 5-day rains over eastern, southwestern and southern parts of Ethiopia whereas no
trends are found in the remaining part of Ethiopia. In general, no trends are found in the yearly maximum length of Kiremt and Belg dry spells (days with rainfall below 1 mm) over Ethiopia. 相似文献
6.
C. Serra M.D. Martínez X. Lana A. Burgueño 《Theoretical and Applied Climatology》2013,114(3-4):531-551
Daily precipitation records of 267 European rain gauges are considered to obtain dry spell length (DSL) series along the second half of the twentieth century. A dry spell consists of consecutive days with daily rain amount below a given threshold, R 0. Four DSL series are obtained for R 0 values equal to 0.1, 1.0, 5.0, and 10.0 mm/day, and their empirical distributions are properly fitted to different statistical models: Pearson type III (PE3), Weibull (WEI), generalised Pareto, (GPA) and lognormal distributions. The parameters of every model are estimated by L-moments, and the goodness of fit is assessed by quantifying discrepancies between empirical and theoretical distributions in the L-skewness–kurtosis diagrams. The most common best-fitting model is PE3, especially for 0.1 and 1.0 mm/day. Nevertheless, a few stations in southern Europe are better modelled by the WEI distribution. For 5.0 and 10.0 mm/day, the spatial distribution of the best-fitting model is more heterogeneous than for the lowest thresholds. While PE3 is still the preferred model for Western Europe, some DSL series are better fitted to WEI or GPA models. Maps of DSL average and standard deviation and expected lengths for return periods of 2, 5, 10, 25, and 50 years show some common features. Whereas for thresholds of 0.1 and 1.0 mm/day, a N–S gradient is detected, especially in Mediterranean areas; for 5.0 and 10.0 mm/day, a NW–SE gradient is observed in the Iberian Peninsula and a SW–NE gradient in the Scandinavian Peninsula. Then, the vicinity to Atlantic and Arctic Oceans and the Mediterranean Sea, as well as orographic features, are more determining factors than the latitude in patterns associated with the highest R 0 thresholds. Finally, a regional frequency analysis based on a clustering algorithm is attempted for the four thresholds R 0, with the PE3 model as the parent distribution for the largest clusters. 相似文献
7.
P. Jonsson I. Eliasson B. Holmer C. S. B. Grimmond 《Theoretical and Applied Climatology》2006,85(3-4):185-201
Summary This study investigates differences in longwave incoming radiation (L↓) within and between three African cities, Dar es Salaam (Tanzania), Ouagadougou (Burkina Faso), and Gaborone (Botswana),
during the dry season, and evaluates the performance of a model to simulate these fluxes. In each city, direct observations
of L↓, shortwave incoming radiation (K↓), air temperature, air humidity, and total suspended particle (TSP) concentration for three land uses (CBD, green residential,
and traditional residential) were taken. The observed L↓ flux decreases with increasing latitude, and temperature becomes an increasingly important factor in governing L↓ variations further from the Equator. Humidity, as well as particle loading, differs significantly between the three cities.
Differences between observed and modelled ɛsky for rural stations near all cities showed a clear diurnal variation, with maximum differences of 0.08 between day and night.
This diurnal difference was incorporated in the model and, for urban areas the model overestimates L↓ by around 25 Wm−2. However, this model performs equally well regardless of the land use considered in any of the cities. The residual (difference
between observed and modelled urban L↓) did not show any correlation with particulate pollution. However, the difference between observed and calculated ɛsky is around 0.05 higher in Ouagadougou compared to the other cities, likely due to the heavy dust load observed here. It is
concluded that tropical urban longwave radiation is not dramatically different from the mid latitudes. 相似文献
8.
L. Sushama S. Ben Said M. N. Khaliq D. Nagesh Kumar R. Laprise 《Climate Dynamics》2014,43(12):3419-3437
Selected characteristics of dry spells and associated trends over India during the 1951–2007 period is studied using two gridded datasets: the Indian Meteorological Department (IMD) and the Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of the water resources (APHRODITE) datasets. Two precipitation thresholds, 1 and 3 mm, are used to define a dry day (and therefore dry spells) in this study. Comparison of the spatial patterns of the dry spell characteristics (mean number of dry days, mean number of dry spells, mean and maximum duration of dry spells) for the annual and summer monsoon period obtained with both datasets agree overall, except for the northernmost part of India. The number of dry days obtained with APHRODITE is larger for this region compared to IMD, which is consistent with the smaller precipitation for the region in APHRODITE. These differences are also visible in the spatial patterns of mean and maximum dry spell durations. Analysis of field significance associated with trends, at the level of 34 predefined meteorological subdivisions over the mainland, suggests better agreement between the two datasets in positive trends associated with number of dry days for the annual and summer monsoon period, for both thresholds. Important differences between the two datasets are noted in the field significance associated with the negative trends. While negative trends in annual maximum duration of dry spells appear field significant for the desert regions according to both datasets, they are found field significant for two regions (Punjab and South Interior Karnataka) for the monsoon period for both datasets. This study, in addition to providing information on the spatial and temporal patterns associated with dry spell characteristics, also allows identification of regions and characteristics where the two datasets agree/disagree. 相似文献
9.
10.
Understanding variations in precipitation from a variety of aspects is important for the utilization of water resources. Based on daily precipitation records at 98 meteorological stations in Sichuan province, southwestern China, the spatial and temporal changes in wet/dry spells were investigated by using 14 precipitation indices. The Mann–Kendall trend test is used to detect trends in the index series. Results suggest that the decrease of precipitation in central and eastern Sichuan was significant in terms of decreasing tendencies of wet spell indices. However, the decreasing trend of dry spell indices suggested an increase in precipitation in western Sichuan province. A higher risk of droughts can be expected in autumn and wet spell indices in winter and spring are increasing, implying obvious seasonality and seasonal shifts of change in precipitation within this province. Wet/dry spells with short duration were accounted for a large proportion of spells in Sichuan. The occurrence and fractional contribution of short-duration wet spells were increasing. The same trend was found in dry spells with short and moderate duration in Sichuan 相似文献
11.
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
12.
The first decades of the rainfall series of Lisbon have been digitized recently allowing a long-term assessment of the rainfall regime for 150 years of uninterrupted, i.e., the first assessment for the longest continuous precipitation time series in western Iberia. This data has been monitored continuously at the D. Luís observatory having started to be published in 1864 in the Observatory's log books (Annals). We use an approach based on different characteristics of rain spells that has been proved to be satisfactory for the analysis of the different parameters related to the rainfall regime in that part of the world. Thus, a rain spell is defined as a series of consecutive days with a measured daily rainfall equal or higher than 1.0 mm. Each rain spell is preceded and followed by at least one dry day. For each rain spell, its duration, its yield (RSY), and its average intensity (RSI) was calculated. Additionally, the total number of rain spells in each year was also considered. Dryness was analyzed using the dry days since last rain approach. Besides the evaluation over the entire 150-year period available, we have also looked into three equally spaced sub-periods. Lisbon reveals large inter-annual and intra-annual variability and both have increased considerably in the last decades. The large intra-annual variability is demonstrated by both; a very large range of annual rainfall percentage accumulated at any given date and by a very large range of dates on which a certain rainfall percentage was accumulated. Again, both metrics increased in the last decades. Parallel to the increase in the uncertainty, a very significant net increase is noticed in the annual totals since the 1960s compared to the first half of the previous century. The increase is mainly due to more intense events which are reflected by higher RSY and RSI values in the last 50 years. 相似文献
13.
Summary Seven series of monthly pluviometric amounts, sometimes exceeding recording periods of 100 years and compiled by the Instituto Nacional de Meteorología (Spain), are used to study the irregularity of the pluviometric regime along the Spanish Mediterranean coast and nearby Atlantic
coast. First of all, three statistical functions (gamma, log-normal and a combination of Poisson and gamma distributions)
and moment-ratio diagrams are used to model the monthly and annual empirical distributions of precipitation amounts, each
distribution being tested by means of the Kolmogorov-Smirnov test. It is noteworthy that, whereas most of the monthly cases
require the gamma distribution, the pluviometric behaviour of the summer months is well described by the Poisson-gamma distribution.
Moreover, both the log-normal and the gamma distributions satisfactorily model empirical annual amounts. Consequently, rainfall
amounts are not identically distributed along a year for each gauge tested. Second, temporal trends deduced for annual and
seasonal amounts are computed and their statistical significance evaluated. The most notable fact is that, although some linear
trends are close to 1 mm/year, their significance levels exceed the assumed threshold value and, excepting the winter season
for Barcelona, they are considered non-significant from a statistical point of view. Finally, by again using monthly and annual
amounts, three temporal irregularity indexes are computed for each pluviometric series, the temporal disparity of the rainfall
patterns of the Mediterranean region being enhanced as a result. It addition to the temporal irregularity, a change with latitude
is observed both in the parameters of the statistical distributions and the temporal irregularity indexes for the rain gauges
analysed. The two most southerly rain gauges constitute a special case in comparison with the remaining stations, because
they also receive the Atlantic influences due to their proximity to this ocean.
Received February 25, 1999/Revised August 2, 1999 相似文献
14.
Aerosol and rain samples were collected between 48°N and 55°S during the KH-08-2 and MR08-06 cruises conducted over the North
and South Pacific Ocean in 2008 and 2009, to estimate dry and wet deposition fluxes of atmospheric inorganic nitrogen (N).
Inorganic N in aerosols was composed of ~68% NH4+ and ~32% NO3– (median values for all data), with ~81% and ~45% of each species being present on fine mode aerosol, respectively. Concentrations
of NH4+ and NO3− in rainwater ranged from 1.7–55 μmol L−1 and 0.16–18 μmol L−1, respectively, accounting for ~87% by NH4+ and ~13% by NO3− of total inorganic N (median values for all data). A significant correlation (r = 0.74, p < 0.05, n = 10) between NH4+ and methanesulfonic acid (MSA) was found in rainwater samples collected over the South Pacific, whereas no significant correlations
were found between NH4+ and MSA in rainwater collected over the subarctic (r = 0.42, p > 0.1, n = 6) and subtropical (r = 0.33, p > 0.5, n = 6) western North Pacific, suggesting that emissions of ammonia (NH3) by marine biological activity from the ocean could become a significant source of NH4+ over the South Pacific. While NO3− was the dominant inorganic N species in dry deposition, inorganic N supplied to surface waters by wet deposition was predominantly
by NH4+ (42–99% of the wet deposition fluxes for total inorganic N). We estimated mean total (dry + wet) deposition fluxes of atmospheric
total inorganic N in the Pacific Ocean to be 32–64 μmol m−2 d−1, with 66–99% of this by wet deposition, indicating that wet deposition plays a more important role in the supply of atmospheric
inorganic N than dry deposition. 相似文献
15.
Dry spells in the River Plata Basin: an approximation of the diagnosis of droughts using daily data 总被引：1，自引：1，他引：0
Walter M. Vargas Gustavo Naumann Juan L. Minetti 《Theoretical and Applied Climatology》2011,104(1-2):159-173
This study addresses the dry spells observed in the La Plata Basin using daily data from 94 observation stations during sampling periods from 1900 to 2005. Dry days were defined as having less than 0.3?mm of accumulated precipitation. This definition allowed for the assessment of the dryness in the La Plata Basin and a comparison with other regions. The main purpose of this study was to analyse dry spells, especially extreme cases (meteorological droughts), and assess them on a daily basis. Trends and low frequency of droughts were analysed using a general framework to detect and compare properties of dry states based on daily and annual time scales. The trends were estimated using two different methods. Overall, the trends showed a decrease, especially in the eastern basin region during the period of 1972?C1996. The results showed sporadic decreases in dry events and events of extreme dryness (droughts). Spectral structure permits an inference of low-frequency maxima and confirmed an inter-annual 2- to 3-year period of variability in drought occurrence for most of the basin. Furthermore, probabilistic distribution functions of dry spells at basin stations were analysed to confirm that they followed a geometric?Cbinomial distribution. Additional tests were used to determine whether there was a second threshold, using the Weibull and gamma adjustment models. In order to study spatial homogeneity, the field of dry spell maxima in the basin was generated using a vector array based on the occurrence date and length of the maximum spell. Due to the dependence of spell length on the annual cycle, the longest spells were observed from April to the beginning of winter in the Argentine northwest region and in the northern and western regions of the basin. The intensity of droughts decreased in the Pampas and Mesopotamia regions. The drought of 1988 was considered to be the longest dry spell in the basin. The water deficits from this drought resulted in Argentinean economic losses of more than four billion US dollars during 1988. 相似文献
16.
Summary During the summer season, typhoons form in the western north Pacific Ocean and travel westward towards China. Some recurve
northward off the coast, whereas others continue in over land. These typhoons bring heavy rainfall to the Huai river basin
in eastern central China. In August 1975, the remnant of typhoon Nina caused exceptionally heavy rainfall in the Hongru river
basin, in the mountainous upper reaches of the Huai river. The rainfall lasted five days from 4 to 8 August. This type of
nearly stationary typhoon can cause rainfall of large intensity for a long duration, and is suitable for maximization to derive
probable maximum precipitation (PMP) estimates. The PMP is transformed into a probable maximum flood hydrograph that is subsequently
used to design spillways etc. In this study the PMP values have been estimated using a hydrometeorological method involving
depth-area-duration analysis, moisture maximization, and altitude adjustment for typhoon Nina, for 1, 2, and 3 days duration.
Areal PMP values were obtained for the entire Hongru river catchment, as well as for the subcatchments upstream the dams at
Banqiao (762 km2), Shimantan (230 km2), Boshan (580 km2), and Suyahu (4 498 km2). For point values, the PMP was estimated to 1 200 mm/day, 1 460 mm/2 days, and 1 910 mm/3 days at altitudes about 100 m,
which agrees well with previous studies.
Received February 21, 1997 Revised May 27, 1997 相似文献
17.
M. R. Ramesh Kumar S. M. Pednekar M. Katsumata M. K. Antony Y. Kuroda A. S. Unnikrishnan 《Theoretical and Applied Climatology》2006,85(1-2):117-122
Summary The diurnal cycle of rainfall over the eastern equatorial Indian Ocean was studied for the period 23rd October 2001 to 31st October 2003 using hourly data from the Triton buoy positioned at 1.5° S and 90° E. An analysis of the active and weak spells
of rainfall for different seasons revealed peaks in the late evening hours in Winter, Summer and Fall and in early morning
hours (in Spring) in 2002. The active spell of rainfall peaked in the afternoon hours, during Winter, Spring and Summer in
2003, which agrees with the previous results of Janowiak et al. (1994). An analysis of rainfall events showed that Fall 2002
had a maximum number of rainfall events (90) and minimum (60) were observed in Spring 2003. Further it was found that the
majority of rain events (>60%) were less than 3 hours in duration throughout the study period. The longer duration rainfall
events (i.e. rain events greater than 6 hour duration) contributed significantly to Spring 2002 (20% of the total rainfall)
and Winter 2003 (21% of the total rainfall). Harmonic analysis of the hourly rainfall data for different seasons revealed
that diurnal harmonic explains more than 80% of the variance for all seasons. Furthermore, the diurnal harmonic has a maximum
amplitude for all seasons except summer, where the semidiurnal and six hourly harmonics are significant. 相似文献
18.
Spatial and temporal analysis of dry spells in Greece 总被引：1，自引：2，他引：1
Chr. Anagnostopoulou P. Maheras T. Karacostas M. Vafiadis 《Theoretical and Applied Climatology》2003,74(1-2):77-91
Summary ?A spatio-temporal analysis of the dry spells that occur in the Greek area is carried out for an extended period of 40 years
(1958–1997). The dry spells can be defined as a number of consecutive days with no rain. The number of days defines the length
of the dry spells. The longest spells are identified in central (Cyclades) and the south-east Aegean Sea whereas dry spells
with the minimum length are shown over the north-west of the Greek area that reflects the significance of the latitude and
the topography. Negative Binomial Distribution and Markov Chains of second order have been used to fit the duration of the
dry spells of different lengths. The study of the seasonal and annual distribution of the frequency of occurrence of dry spells
revealed that the dry spells in Greece depict a seasonal character, while medium and long sequences are associated with the
duration and hazards of drought.
Received February 20, 2002; revised September 5, 2002; accepted October 6, 2002 相似文献
19.
Summary ?Evapotranspiration characteristics on the point-scale (several hundred square meters) and the local scale (several square
kilometers) are analysed by comparing a deterministic and a statistical – deterministic surface energy balance model. The
vegetation surface variability is represented by both the surface heterogeneity and inhomogeneity. Heterogeneity means the
mosaic of wet (wif ≠ 0) and dry (1-wif) fractions of vegetation surface, while inhomogeneity addresses small scale variations of soil moisture content.
The microscale characteristics of evapotranspiration are considered in terms of analysing evapotranspiration E
v
versus soil moisture content θ, relative frequency distribution characteristics of E
v
(θ) and the aggregation algorithms for its estimation. The analyses are performed for loam soil type under different atmospheric
forcing conditions.
The main result is as follows: For dry vegetation surface (wif = 0), the relationship between the aggregated (θagg) and the area-averaged (θ
m
) soil moisture content is nonlinear and depends on both the states of the surface and the atmospheric forcing conditions.
In the study, we assumed that there are no advective effects and mesoscale circulation patterns induced by surface discontinuities.
Based on this fact it seems unlikely to be able to construct an aggregation algorithm for calculating θagg without inclusion of the atmospheric forcing conditions. This means that it will be difficult to construct a simple formula
for calculating area-averaged transpiration, if it is possible at all.
Received May 3, 2001; revised May 31, 2002; accepted June 3, 2002 相似文献
20.
Modelling Wet and Dry Spells with Mixture Distributions 总被引：1，自引：0，他引：1
Summary The object of the study is to develop a discrete precipitation model which is able to simulate local, daily series of precipitation
occurrences. The model is fitted to the observed data of two stations, Szeged and Szombathely, in Hungary (1951–1995), with
pronounced attention to the reproduction of long dry periods, as characteristic features of the climate in Central Europe.
The point of the approach is to model the duration of consecutive dry and wet series, i.e., spells, instead of individual
wet or dry days. After having comparisons of three different aspects performed, the selected precipitation threshold is 0.1 mm.
This threshold keeps the duration of dry and wet periods more or less balanced, whereas the value of the threshold does not
fundamentally influence either the conditional distribution of macrocirculation types or the local weather statistics related
to the so defined wet or dry days. The duration of both wet and dry spells are found to be independent of the length of either
the preceding (opposite) or the last, but one (identical) state. It is also demonstrated that mixed distributions fairly fit
to the wet and dry spells, whereas the simple geometric does not, especially due to the erroneous lack of long dry sequences.
Weighted sum of two geometric distributions, as well as that of one geometric and one Poisson distribution exhibits good fitting
for the dry spells, whereas only the latter one can be advised to employ for the wet periods. Parameters of the distributions
obviously depend on the season and the site, in question.
Received June 30, 1999 Revised February 3, 2000 相似文献