ISSN:0148-0227    

DOI:10.1029/JD095iD03p01985

年代:1990

数据来源: WILEY

摘要:

Analysis of the surface distribution of precipitation associated with intense extratropical cyclones reveals elongated maxima aligned with the steering flow. Rapidly intensifying cyclones create precipitation maxima which are better defined and contain more moisture than weaker cyclones. The distributions are associated with the formation of a precipitation generating zone (PGZ) aligned with the midtropospheric jet ahead of and parallel to the surface cold front extending southward from the surface low. These zones tend to move along their axes and are host to the most frequent and intense convective activity in the extratropical cyclone. Hourly rain gage measurements at sites in their path indicate an average of three precipitation peaks in 16 storms studied, although radar echoes disclose that many mesoscale structures with high reflectivity are simultaneously active. It is hypothesized that formation of such zones is most pronounced when momentum transport out of the jet increases the advection of warm moist air at low levels, thereby sustaining or increasing convective instability. In this context, the PGZ becomes the dominant feature of the extratropical cyclone and is crucial to intensification.

ISSN:0148-0227    

DOI:10.1029/JD095iD03p01987

年代:1990

数据来源: WILEY

摘要:

Two common properties of empirical moments shared by spatial rainfall, river flows, and turbulent velocities are identified: namely, the log‐log linearity of moments with spatial scale and the concavity of corresponding slopes with respect to the order of the moments. A general class of continuous multiplicative processes is constructed to provide a theoretical framework for these observations. Specifically, the class of log‐Levy‐stable processes, which includes the lognormal as a special case, is analyzed. This analysis builds on some mathematical results for simple scaling processes. The general class of multiplicative processes is shown to be characterized by an invariance property of their probability distributions with respect to rescaling by a positive random function of the scale parameter. It is referred to as (strict sense) multiscaling. This theory provides a foundation for studying spatial variability in a variety of hydrologic processes across a broad range of s

ISSN:0148-0227    

DOI:10.1029/JD095iD03p01999

年代:1990

数据来源: WILEY

摘要:

Information on the spatial and temporal statistics of rain rate is needed for the design of remote sensing systems for the measurement of areal rainfall accumulation and for the design of millimeter wave communication systems. In this study, rain gage and radar data were used to determine empirically the spatial and temporal structure of the rain process as observed using rain rate as a tracer of the atmospheric motions and to test the validity of Taylor's hypothesis for relating their spatial and temporal statistics. Weather radar derived rain rate maps were employed to obtain one‐ and two‐dimensional spatial power spectra. Azimuthally averaged two‐dimensional spectra displayed the shape predicted for a passive scalar advected by a steady state field of two‐dimensional turbulence driven by the input of energy over a narrow band of wave numbers. One‐dimensional spatial spectra for a short line of rain gages had the same spectral shape as the azimuthally averaged spectra obtained from the radar data. Temporal spectra from the gage time series were nearly identical in shape to the one‐dimensional spatial spectra if less than a half hour of data were processed to generate a spectrum and a constant translation velocity was assumed to relate the temporal and spatial scales. For spectra corresponding to longer durations, a match could

ISSN:0148-0227    

DOI:10.1029/JD095iD03p02011

年代:1990

数据来源: WILEY

摘要:

The extreme variability of cloud and rain fields poses serious problems in quantitative use of remotely sensed satellite and radar data. We show how to characterize this variability using scale invariant (sensor resolution independent) codimension functions which are exponents characterizing the probability distributions. These codimension functions in turn form a three parameter universality class. We review the properties of these multifractal measures and empirically evaluate the codimension functions as well as the universality classes for infrared and visible satellite cloud images using the new probability distribution/multiple scaling technique, refining previously published results and relating these to the established lognormal rain and cloud phenomenologies. We then show how to solve the radar observers' problem for multifractal radar reflectivity factors and to estimate the codimension function of rain from the radar. Finally, we reexamine some earlier (monofractal) analysis techniques in the light of our findings.

ISSN:0148-0227    

DOI:10.1029/JD095iD03p02021

年代:1990

数据来源: WILEY

摘要:

The spatial distribution of cumulus clouds is assumed to be the result of the effects of convective activity on the thermodynamic environment. These effects can be parameterized in terms of a stabilization function representing the time rate of change of convective available potential energy. Using these results, a new inhibition hypothesis explaining the expected characteristics of the spatial distribution of cumulus clouds is postulated. This paper performs a verification of the inhibition hypothesis on real and simulated cloud fields. In order to do so, an objective measure of the spatial characteristics of cumulus clouds is introduced. Multiple cloud experiments are performed with a three‐dimensional numerical cloud model. Skylab pictures of real cumuli are also used in the verification. Results of applying this measure to simulated and observed cumulus cloud fields confirm the inhibition hypothesi

ISSN:0148-0227    

DOI:10.1029/JD095iD03p02035

年代:1990

数据来源: WILEY

摘要:

Is there an intrinsic characteristic of free moist atmospheric convection that induces a particular type of space‐time structure within cloud fields? What is the expected nature of the spatial distribution of cumuli within unforced cumulus cloud fields? This paper is one of two in this collection that addresses these fundamental questions. The thermodynamic effects of convection are quantified as functions of changes of convective available potential energy (CAPE) induced by the convective overturning. The time rate of change of CAPE is parameterized in terms of a kernel of influence or stabilization function. A three‐dimensional cloud model is used to infer and quantify stabilization functions by performing single‐cloud experiments. Measured stabilization functions are positive everywhere, decreasing away from the cloud center. Stabilization functions are decomposed into various thermodynamic contributions involving pressure, temperature, and moisture changes in the boundary layer and above. It is observed that the major contribution to the environmental stabilization comes from the drying of the planetary boundary layer induced by subsidence. The thermodynamic effect of nonprecipitating and precipitating convection is to reduce CAPE in the surrounding environment and hence reduce the conditional probability of further convection nearby. A new hypothesis with respect to the spatial distribution of cumuli is postulated. The inhibition hypothesis states that, under completely homogeneous external conditions and assuming a spatially random distribution of cloud‐trigering mechanisms, the spatial distribution of cumuli in the resulting cloud field must be regular, as opposed to either random or clustered, because cumulus clouds tend to reduce the available energy for convection, thereby inhibiting further convection

ISSN:0148-0227    

DOI:10.1029/JD095iD03p02047

年代:1990

数据来源: WILEY

摘要:

Extreme rainstorms play an important role in the hydrologic design and operation of water resource systems. Due to the lack of complete knowledge of the complex meteorological mechanisms that produce and sustain extreme storms, statistical and correlation analyses are a valuable and complementary tool in identifying regularities of extreme rainfall characteristics. In this paper we have studied the statistical properties of several characteristics of extreme midwestern storms. In particular, we have analyzed the storm occurrence process in space and time, storm shape and orientation, total storm center depth, storm duration, storm areal extent, and depth‐area relationships. Our analysis is based on the data base of extreme storms published by the U.S. Army Corps of Engineers. Several trends and regularities among extreme midwestern storms have been identified and are expected to prove useful in developing and/or evaluating empirical and physically based models of extreme rainfal

ISSN:0148-0227    

DOI:10.1029/JD095iD03p02061

年代:1990

数据来源: WILEY

摘要:

In the 24‐hour period beginning 2300 UTC on August 4, 1986, an intense east coast cyclone produced 328 mm of rain in Sydney, Australia, causing widespread flooding. The operational quantitative precipitation forecast, based on 150‐km resolution, was poor, predicting only 16 mm of rain. In this study, numerical simulations of this event are carried out after modifying the large‐scale and cumulus convection precipitation mechanisms. These changes make the mechanisms mutually exclusive at a given time and grid point, and more sensitive to orographic forcing and surface energy fluxes. Marked improvement in the amounts of predicted rainfall occurs as the horizontal resolution of the model increases. These results indicate that mesoscale processes play an important role in determining rainfall amounts associated with east coast cyclones and demonstrate the potential to accurately simulate very heavy rainfall e

ISSN:0148-0227    

DOI:10.1029/JD095iD03p02073

年代:1990

数据来源: WILEY

摘要:

A model of storm rainfall is developed for the central Appalachian region of the United States. The model represents the temporal occurrence of major storms and, for a given storm, the spatial distribution of storm rainfall. Spatial inhomogeneities of storm rainfall and temporal inhomogeneities of the storm occurrence process are explicitly represented. The model is used for estimating recurrence intervals of extreme storms. The parameter estimation procedure developed for the model is based on the substitution principle (method of moments) and requires data from a network of rain gages. The model is applied to a 5000 mi2(12,950 km2) region in the Valley and Ridge Province of Virginia and West Virginia.

ISSN:0148-0227    

DOI:10.1029/JD095iD03p02083

年代:1990

数据来源: WILEY