Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: William Porch x
  • Refine by Access: All Content x
Clear All Modify Search
William Porch
and
Daniel Rodriguez

Abstract

Diagnostic wind field numerical models have significant difficulty developing representative wind velocities in complex terrain. A large of this difficulty begins with the initial wind field interpolation. If this interpolated wind field does not closely represent the true winder mass-consistent adjustments cannot retrieve the correct atmospheric flow patterns. Presently, the initial interpolation in diagnostic models is almost exclusively done using a simple one-over-separation-squared (1/r 2) interpolation algorithm. This algorithm uses the closest or larger number of measurements of the wind velocity closest to the interpolation location. In this paper, we explore different interpolation algorithms using not only the measurement field at the interpolation time, but also the statistical relationships between stations. These algorithms were tested with data from the 1980 Atmospheric Studies in Complex Terrain (ASCOT) sponsored by the Department of Energy. The results show that, while consistent (though in most cases marginal) improvement in interpolated wind speeds was obtained, little improvement was derived for interpolated wind direction.

Full access
William M. Porch
and
Dale A. Gillette

Abstract

Fast-response light scattering measurements at two heights during a Texas dust storm are combined with horizontal and vertical wind data to derive and compare aerosol flux estimates using three techniques. The major result of this study is that a relative equivalence exists between the fine-particle (0.1 μm < radius < 1 μm) exchange coefficient and the eddy viscosity of the wind. The data also shed some light on the complex dependence of wind speed threshold for suspension and aerosol flux in high winds for different surface conditions and soil types. These results show the value of the experimental technique to studies of toxic particulate suspension and deposition by wind.

Full access
William M. Porch
and
David B. Smith
Full access
R. L. Coulter
,
Monte Orgill
, and
William Porch

Abstract

Measurements in a tributary to Brush Creek Valley during the September and October 1984 ASCOT campaign with laser anemometers, tethersondes, a minisodar, and smoke release were used to calculate the contribution by tributaries to nocturnal drainage flow from the main valley. Four experimental nights with different mesoscale wind regimes were used in the study. It was found that a simple picture of mass flux proportional to drainage area is not sufficient to predict the relative contributions of drainage basins. The exposure of the slopes within the tributaries to the external wind regime was found to be a significant factor in the contribution of the upper regions of the tributary; but drainage from the well-protected lower region was found to be stronger when the external wind direction was opposite to the drainage direction than when the external wind was along the drainage direction. A circulation cell that introduces mass into the tributary system both from the main canyon flow and from the side opposite the main canyon flow is proposed to explain this effect.

Data from the morning hours after flow reversal has occurred in the main canyon show continued drainage in the tributary for up to two hours. The data are used to show that this is probably due to continued radiational cooling of the protected sidewalls in the tributary.

Full access
William M. Porch
,
William E. Clements
, and
Richard L. Coulter

Abstract

This paper describes a regular oscillation observed in nighttime drainage airflow in a valley under relatively light upper-level wind conditions. The period of these oscillations is about 20 minutes with at least one harmonic at about 10 minutes. A strong coherence between tributary flow and main valley fluctuations was observed, with the phase of the tributary flow leading the valley oscillation; this indicates the importance of tributaries as major contributors to the dynamics of cold air flow in valleys.

Full access
Richard L. Coulter
,
Timothy J. Martin
, and
William M. Porch

Abstract

The characteristics of tributary drainage flow in stable, nocturnal conditions in three closely located tributaries are compared. The orientation of the tributaries with respect to Kimball Creek, into which they drain, appears to be a controlling factor in the tributary flow. In particular, oscillations in the drainage flow are found to be weakest and drainage mass per unit area greatest in the tributary most closely aligned with the main canyon.

Full access
David S. Ensor
,
William M. Porch
,
Michael J. Pilat
, and
Robert J. Charlson

Abstract

The possible climatic effects of the secular increase of aerosols from man's activities have been coupled with the microphysics of the aerosol properties. The magnitude of the critical aerosol absorption coefficient to backscatter coefficient, (b abs / b bs ) critical , was estimated for a model atmosphere corresponding to cooling or heating of the earth with increasing aerosol concentration. The b abs /b bs ratio was calculated with Mie theory assuming a Junge particle size distribution and spherical particles as a function of the imaginary part of the particle refractive index (particle light absorption) and the size distribution slope. Comparing the b abs /b bs ratio calculated from Mie theory to the critical b abs / b bs , cooling might ensue if the imaginary part is less than 10−3 while heating may result if it is greater than 0.1.

Full access
William M. Porch
,
Richard B. Fritz
,
Richard L. Coulter
, and
Paul H. Gudiksen

Abstract

Field experiments measuring nocturnal tributary flows have shown complex internal structure. Variations in the flow range from short-term (8–16 min) oscillations (related to tributary/valley flow interactions) to long-term flow changes throughout the night (related to upper ridge slope and tributary sidewall cooling rate changes). The mean vertical structure in the tributary flow shows a three layer structure. Outflow winds are observed near the surface and in an elevated jet up to several hundred meters height. A flow minimum or counterflow exists at about the height of the drainage flow maximum in the main valley. Comparisons of flow volumes and variations from a single large tributary show that 5%–15% of the nocturnal flow in the main valley may be contributed through one tributary. This implies that tributaries may dominate main valley sidewall and midvalley subsidence contributions to valley drainage flows.

Full access