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71.
On the relationship of thunderstorm ice hydrometeor characteristics and total lightning measurements 总被引:1,自引:0,他引:1
Wiebke Deierling John Latham Walter A. Petersen Scott M. Ellis Hugh J. Christian Jr. 《Atmospheric Research》2005,76(1-4):114
Satellite-borne and ground-based devices for the detection of lightning offer the opportunity to explore relationships–on all significant scales up to global–between lightning frequency, f, and other thundercloud parameters. Calculations predict that f is proportional to the product of the downflux p of solid precipitation and the upward mass flux, I, of ice crystals. This prediction has received support from limited computational studies. The physical reasons for such a relationship are explained in terms of the paramount role of ice in the electrification of thunderstorms. Herein, this prediction is subjected to further, preliminary examination through analysis of lightning and dual-polarimetric radar data collected during the STERAO experiment conducted in Northern Colorado during the summer of 1996. The analysis has yielded some highly provisional support for this flux hypothesis. Computed trends of radar derived hydrometeor fractions of solid precipitation and small ice show correlation to the total lightning frequency and raise the possibility of determining values of p and/or I from lightning measurements.It is shown that the extent to which the observed correlations between f and both solid precipitation and small ice trends are or are not strong can provide an indication as to whether the lightning activity is limited by the available concentrations of precipitating or non-precipitating ice in the upper regions of the charging zone of the thundercloud, where most of the charge transfer occurs. It is demonstrated that the most accurate determinations of precipitation rate p from measurements of lighting frequency f are likely to be for conditions where the field-growth is limited by the availability of graupel pellets. It is shown that the simultaneous time variations of f and solid precipitation trends of the type obtained in the STERAO experiment could enable us to determine the nature of the dominant glaciation process operative in the thunderclouds studied. 相似文献
72.
Short-term risk forecasts of point precipitation are obtained with COTREC/RainCast, a technique for extrapolation of radar images. The risk forecasts are updated every 5 min for the next 0–2 h. Risk levels are defined for moderate, heavy and extreme precipitation. Warning messages are generated if, at the locations of 23 rain gauges, these risk levels are reached or exceeded. The time-resolved gauge data are used to judge if the warning messages are in time, early or late.Data over a period of 4 months (summer 2002) are used for verification. The largest number of warnings (1790) was obtained for moderate precipitation. About 55% of these warnings were in time, 23% were early and 22% were late. This finding is in a good agreement with the defined risk level for warnings (50%), indicating that the model for calculating the risk factors is reliable. Less warnings in time, and more late warnings were found for heavy and extreme precipitation. Hence, the risk levels need to be lowered for heavy and extreme precipitation, in order to reduce the number of late warnings. 相似文献
73.
Fadong Li Xianfang Song Changyuan Tang Changming Liu Jingjie Yu Wanjun Zhang 《Environmental Geology》2007,53(3):687-696
The groundwater in headwater region is an important recharge source for the adjacent mountain-front plain. In order to reveal
the relationship among precipitation, soil water and groundwater, from June to September in 2004, stable isotopes (deuterium
and oxygen-18) in precipitation and soil waters at the depths of 10, 20, 30, 50, 70, 90, and 110 cm were analyzed at two sites
covered by black locust (Robinia Pseudoacia L.) (Site A) and grass predominated by Themeda triandra (T. japonica (Willd.) Tanaka) and Bothriochloa ischaemum (B. ischaemum (L.) Keng) (Site B) in an experimental catchment at Taihang Mt., North China, respectively. The δ18O of precipitation in daily rain events shows large variations (−13.3 to −4.3‰) with a mean of 8.1‰. The δ18O and δ D of soil waters along profiles in two sites suggest that the influence of canopy cover was just up to 10 cm in top
soil water. The soil water moved over the zero flux plane at 70 cm in-depth is expected to escape the evaporative effect at
the end of September in both sites. The results show that the stable isotope, instead of tritium as tradition, can be used
to trace the soil water behaviors based on the movement of isotopic peak along the vertical profiles in this semi-arid and
semi-humid mountainous region. The infiltration depths of soil water in Taihang Mt. are 12 and 10 mm/day from June to September
in 2004 in Site A and Site B, respectively. Tracing by stable isotope, recharge fluxes of soil water to local groundwater
are of 3.8 and 3.2 mm/day in Site A and Site B, respectively. The results provide desirable information for assessment of
local groundwater resources.
An erratum to this article can be found at 相似文献
74.
The stable isotopes of oxygen and hydrogen were used to determine the seasonal contributions of precipitation to groundwater
recharge at a forested catchment area in the upper North Han River basin, Korea. A comparison of the stable isotopic signatures
of groundwater and precipitation indicates that the precipitations which occurred during both the dry and rainy seasons are
the important source of groundwater recharge in this region. A stable isotopic signature shown in the stream waters at the
upstream reaches is similar to that of groundwaters, indicating that stream waters are mostly fed by groundwater discharge.
Reservoir waters in the downstream flood control dams have lower deuterium excess values or d-values compared with those of the upstream waters, indicating a secondary evaporative enrichment. These results can provide
a basis for the effective management of groundwater and stream water resources in the North Han River basin. 相似文献
75.
Dev Niyogi Hsin-I Chang Fei Chen Lianhong Gu Anil Kumar Surabi Menon Roger A. Pielke Sr. 《Natural Hazards》2007,42(2):345-359
Aerosols can affect the cloud-radiation feedback and the precipitation over the Indian monsoon region. In this paper, we propose
that another pathway by which aerosols can modulate the multi-scale aspect of Indian monsoons is by altering the land–atmosphere
interactions. The nonlinear feedbacks due to aerosol/diffuse radiation on coupled interactions over the Indian monsoon region
are studied by: (1) reviewing recent field measurements and modeling studies, (2) analyzing the MODIS and AERONET aerosol
optical depth datasets, and (3) diagnosing the results from sensitivity experiments using a mesoscale modeling system. The
results of this study suggest that the large magnitude of aerosol loading and its impact on land–atmosphere interactions can
significantly influence the mesoscale monsoonal characteristics in the Indo-Ganges Basin. 相似文献
76.
Sensitivity of Mesoscale Model Forecast During a Satellite Launch to Different Cumulus Parameterization Schemes in MM5 总被引:1,自引:0,他引:1
The identification of the model discrepancy and skill is crucial when a forecast is issued. The characterization of the model
errors for different cumulus parameterization schemes (CPSs) provides more confidence on the model outputs and qualifies which
CPSs are to be used for better forecasts. Cases of good/bad skill scores can be isolated and clustered into weather systems
to identify the atmospheric structures that cause difficulties to the forecasts. The objective of this work is to study the
sensitivity of weather forecast, produced using the PSU-NCAR Mesoscale Model version 5 (MM5) during the launch of an Indian
satellite on 5th May, 2005, to the way in which convective processes are parameterized in the model. The real-time MM5 simulations
were made for providing the weather conditions near the launch station Sriharikota (SHAR). A total of 10 simulations (each
of 48 h) for the period 25th April to 04th May, 2005 over the Indian region and surrounding oceans were made using different
CPSs. The 24 h and 48 h model predicted wind, temperature and moisture fields for different CPSs, namely the Kuo, Grell, Kain-Fritsch
and Betts-Miller, are statistically evaluated by calculating parameters such as mean bias, root-mean-squares error (RMSE),
and correlation coefficients by comparison with radiosonde observation. The performance of the different CPSs, in simulating
the area of rainfall is evaluated by calculating bias scores (BSs) and equitable threat scores (ETSs). In order to compute
BSs and ETSs the model predicted rainfall is compared with Tropical Rainfall Measuring Mission (TRMM) observed rainfall. It
was observed that model simulated wind and temperature fields by all the CPSs are in reasonable agreement with that of radiosonde
observation. The RMSE of wind speed, temperature and relative humidity do not show significant differences among the four
CPSs. Temperature and relative humidity were overestimated by all the CPSs, while wind speed is underestimated, except in
the upper levels. The model predicted moisture fields by all CPSs show substantial disagreement when compared with observation.
Grell scheme outperforms the other CPSs in simulating wind speed, temperature and relative humidity, particularly in the upper
levels, which implies that representing entrainment/detrainment in the cloud column may not necessarily be a beneficial assumption
in tropical atmospheres. It is observed that MM5 overestimates the area of light precipitation, while the area of heavy precipitation
is underestimated. The least predictive skill shown by Kuo for light and moderate precipitation asserts that this scheme is
more suitable for larger grid scale (>30 km). In the predictive skill for the area of light precipitation the Betts-Miller
scheme has a clear edge over the other CPSs. The evaluation of the MM5 model for different CPSs conducted during this study
is only for a particular synoptic situation. More detailed studies however, are required to assess the forecast skill of the
CPSs for different synoptic situations. 相似文献
77.
文中分析了庆阳地区春季降水气候特征和环流形势 ,用 1995~ 1998年 3~ 5月T10 6资料建立了该区 8县 (市 )春季降水、温度MOS预报方程 ,进行了回代检验和试报 ,并提出了模式更换后的处理方法 相似文献
78.
79.
80.
R. V. Rohli A. J. Vega M. R. Binkley S. D. Britton H. E. Heckman J. M. Jenkins Y. Ono D. E. Sheeler 《Applied geography (Sevenoaks, England)》2001,21(4)
Impacts on water resources caused by human activity, natural climate variation and long-term climate change are unclear in the US Great Lakes region. Improved understanding of the impact of atmospheric circulation on stream discharge variability into the Lakes is thus important. In this analysis, monthly surface and mid-tropospheric circulation patterns suggest that surface pressure variations over Missouri and Illinois are most strongly correlated to discharge. The mid-tropospheric patterns most directly related to discharge place the Great Lakes in a trough-to-ridge flow pattern. The analysis confirms that at this scale, lee shore advection resulting in ‘lake-effect’ precipitation is not very important to regional discharge, and neither are variations in the Pacific–North American teleconnection. 相似文献