Search Results

You are looking at 1 - 10 of 15 items for

  • Author or Editor: Richard E. Passarelli Jr. x
  • Refine by Access: All Content x
Clear All Modify Search
Richard E. Passarelli Jr.

Abstract

The theory of parametric techniques for the recovery of Doppler spectral moments from ground-clutter-contaminated measurements of the radar autocorrelation function is presented. Seven algorithms for the mean velocity are given as examples, and evaluated using simulated Gaussian weather and measured ground clutter signals. Some algorithms can provide accurate estimates of the mean velocity at clutter-to-signal power ratios of > 10 dB and one performs well at 20 dB. An example in actual precipitation is also presented.

Full access
Richard E. Passarelli Jr.

Abstract

It is well known that snowflakes tend to distribute exponentially with respect to their melted diameter. This fact is used to formulate an approximate analytical model of the deposition and aggregation growth of snow in stratiform clouds. The model predicts the height evolution in a steady-state, vertically heterogeneous cloud of the slope and intercept parameters, N(h) and λ (h), of the size distribution of snowflakes which is assumed to be given by n(D,h)=N(h) exp[−λ(h)D], where h is the height in the cloud and D the snowflake diameter. Solutions for N(t) and λ(t) for a time-dependent spatially homogeneous cloud are also presented. Results from this technique compare well with numerical integrations for the case of perfect geometric coalescence of raindrops. This stratiform snow model predicts the existence of radar reflectivity-snowfall rate relations although, for this first-order model, there is fair agreement between theoretical and observed values. The model suggests that “equilibrium” snow size spectra owe their existence to the counteracting effects of deposition and aggregation growth.

Full access
Richard E. Passarelli Jr.

Abstract

Mean snowflake collection efficiencies can be estimated by studying the height evolution of snow-size spectra in natural precipitation. This was done using coordinated aircraft and Doppler radar measurements of snow-size spectra and analytical and numerical techniques to model the stochastic collection process. For aggregating stellar and dendritic crystals in the temperature range −15 to −12°C the estimated mean collection efficiency was 1.4±0.6.

Full access
Richard E. Passarelli Jr.

Abstract

No Abstract

Full access
Bernard Vonnegut
and
Richard E. Passarelli Jr.

Abstract

Full access
Richard E. Passarelli Jr.
and
Hannah Boehme

Abstract

Topographic forcing over the hills and small mountains of southern New England plays an important role in determining the distribution of pre-warm-front precipitation from winter cyclones. Upslope regions receive 20–60% more precipitation than do nearby downslope or coastal regions. Both the intensity and duration of precipitation contribute to the positive upslope anomalies. The magnitude of the upslope anomalies, the details of the precipitation intensity distributions at proximal upslope and downslope gauges, and the results of simple models indicate that precipitation scavenging in orographic clouds can explain the orographic enhancement. Also, the existence of a positive precipitation anomaly over the coastal plain suggests that frictional convergence may be generating weak, but persistent vertical motions.

Full access
Richard E. Passarelli Jr.
and
Roscoe R. Braham Jr.

Radar and aircraft data are presented, in the form of case studies, for three shoreline-parallel snow bands that occurred over Lake Michigan. In all three cases a winter land breeze from one or both shores is shown to have an important role in organizing the low-level convergence and convective motions. These cases are compared with earlier studies of lake-effect snow bands on Lakes Erie and Ontario.

Full access
Richard E. Passarelli Jr.
and
Alan D. Siggia

Abstract

The relationships between the Doppler spectrum of velocities and the autocorrelation function can be studied via simple geometric and power series expansion relations. The asymptotic expansion of the autocorrelation function in terms of the central moments of the Doppler spectrum provides a new theoretical framework for time-domain spectral moment estimation and illustrates the trade-offs in optimal moment estimation. A number of new moment estimators are derived via this general approach and evaluations of three new spectral width estimators demonstrate that the implementation of a single spectral width estimator is generally not the best approach.

Full access
Richard E. Passarelli Jr.
and
Ramesh C. Srivastava

Abstract

Unlike raindrops, ice particles of the same mass can have different fallspeeds, due to variations in the particle shape and bulk density. (This is an extension of the popular axiom that no two snowflakes are alike.) This is an additional source of variance for vertical incidence Doppler (VID) spectra taken in snow that has been neglected in previous studies which assume a one-to-one fallspeed-mass relationship. The total VID spectral variance due to the dispersion of ice particle fallspeeds can be broken down into two components, i.e., that due to the mean fallspeed-mass relationship and that due to fluctuations about the mean. Existing data on ice particle fallspeeds are not adequate for a thorough evaluation, but do indicate that these two sources of fallspeed variance can be of the same order. These results suggest that the task of deducing snow-size spectra from VID measurements is more difficult than has been recognized.

Full access
Richard E. Passarelli Jr.
,
Henry Chessin
, and
Bernard Vonnegut

Abstract

A technique is described for using dilatometers to measure and compare the freezing temperature of water in the presence of various nucleation catalysts. Nucleation is indicated by the increase in volume that water undergone upon freezing.

Full access