Search Results

You are looking at 1 - 10 of 29 items for

  • Author or Editor: Robert M. Brown x
  • Refine by Access: All Content x
Clear All Modify Search
Benjamin M. Herman
,
S. Robert Browning
, and
Robert Rabinoff

Abstract

The changes in the earth-atmosphere albedo and radiative equilibrium temperature due to perturbations in the solar radiative balance are investigated. The perturbations are induced through the introduction of varying amounts of aerosols into the stratospheric layer between 15 and 25 km. Results are presented graphically as a function of latitude and season for a range of aerosol absorption coefficients and for a specific aerosol composed of a 75% sulphuric acid solution. These results indicate that such aerosol perturbations on the solar energy field result in larger albedo and radiative equilibrium changes in polar latitudes than in middle or tropical latitudes.

Full access
Gilbert S. Raynor
,
Paul Michael
,
Robert M. Brown
, and
S. Sethuraman

Abstract

A research program is in progress at Brookhaven National Laboratory to determine the nature of atmospheric diffusion from a representative oceanic site, to relate observed diffusion patterns to meteorological and oceanographic variables, and to develop models to describe such diffusion. The program was initiated in response to plans for construction of offshore nuclear power plants.

Tracer experiments are conducted utilizing oil-fog smoke released from a boat stationed from 1–3 mi off-shore during onshore flows. The smoke is photographed from above and from the side to document lateral and vertical spread. The crosswind concentration distribution is measured by vehicle- and boat-mounted densitometers during successive traverses across the plume. Wind, turbulence and temperature at several levels are measured on the beach by tower-mounted instruments. Temperature profiles at greater heights are measured by kytoon- and aircraft-borne sensors. Water temperatures are also measured. Winds aloft are determined by pibal ascents and turbulence at various altitudes is sampled by an aircraft-mounted variometer.

Preliminary results show that diffusion is governed primarily by water and air temperature differences. With colder water, low-level air is very stable and diffusion minimal but water warmer than the air induces vigorous diffusion. Measurements of plume width and height have been obtained which are smaller and of normalized concentration which are larger than those predicted for the Pasquill F category. Measured values of plume width can be predicted from Eulerian measurements at the beach.

Full access
Gilbert S. Raynor
,
Robert M. Brown
, and
S. SethuRaman

Abstract

Experiments were conducted to investigate the differences in diffusion from an obstacle to free air flow in the ocean and from an undisturbed ocean site. A small island was used as the obstacle and simultaneous releases of oil-fog smoke were made from the island and from a nearby boat. The widths of the plumes and their concentration distributions were measured quantitatively during traverses across the plumes by a second boat. Extensive series of photographs were taken of the plumes from the surface and from the air. Meteorological measurements were made at two locations on the island, from the boats and from an aircraft. One test series was conducted during unstable conditions and a second series with neutral and stable conditions.

Width of the island plume over short periods was from 1.5 to 4 times that of the boat plume with the greatest difference during stable periods. Over longer periods, the differences were somewhat greater and much of the dispersion was caused by plume meander. Height of the island plume averaged about twice that of the boat plume. Normalized maximum centerline concentrations from the boat plume were 1.4 times those of the island plume during unstable periods but about twice during stable and neutral conditions. Averaged over all tests, dispersion from the island was about twice as great as from the boat.

Full access
Benjamin M. Herman
,
Samuel R. Browning
, and
Robert J. Curran

Abstract

Theoretical computations of the intensity and polarization of diffusively transmitted sunlight are presented for two wavelengths, λ = 4290 Å and λ = 5000 Å. The computations are for atmospheres containing various distributions of aerosols, as well as normal molecular constituents, and allow for all significant orders of scattering. The theoretical computations are compared with observations, and it is shown that inclusion of aerosols in the theoretical models results in considerably better agreement between observation and theory than can be achieved by assuming a pure molecular atmosphere for the theoretical computations.

Full access
Todd P. Lane
,
Robert D. Sharman
,
Rod G. Frehlich
, and
John M. Brown

Abstract

This study uses a series of numerical simulations to examine the structure of the wake of the Hawaiian island of Kauai. The primary focus is on the conditions on 26 June 2003, which was the day of the demise of the Helios aircraft within Kauai’s wake. The simulations show that, in an east-northeasterly trade wind flow, Kauai produces a well-defined wake that can extend 40 km downstream of the island. The wake is bounded to the north and south by regions of strong vertical and horizontal shear—that is, shear lines. These shear lines mark the edge of the wake in the horizontal plane and are aligned approximately parallel to the upstream flow direction at each respective height. The highest-resolution simulations show that these shear lines can become unstable and break down through Kelvin–Helmholtz instability. The breakdown generates turbulent eddies that are advected both downstream and into the recirculating wake flow. Turbulence statistics are estimated from the simulation using a technique that analyzes model-derived structure functions. A number of sensitivity studies are also completed to determine the influence of the upstream conditions on the structure of the wake. These simulations show that directional shear controls the tilt of the wake in the north–south plane with height. These simulations also show that at lower incident wind speeds the wake has a qualitatively similar structure but is less turbulent. At higher wind speeds, the flow regime changes, strong gravity waves are generated, and the wake is poorly defined. These results are consistent with previous idealized studies of stratified flow over isolated obstacles.

Full access
Ian M. Giammanco
,
Tanya M. Brown
,
Rosemarie G. Grant
,
Douglas L. Dewey
,
Jon D. Hodel
, and
Robert A. Stumpf

Abstract

Throughout historical literature anecdotal or visual observations have been used to describe the hardness property of hailstones (e.g., hard, soft, slushy). A unique field measurement device was designed and built to apply a compressive force to the point of fracture on hailstones in the field. The device uses a pistol-grip clamp to apply a compressive load to a hailstone and integrates a fast-response load cell and associated data acquisition components to measure the applied force through the point of fracture. The strain rate applied to the stone is fast enough to produce a brittle failure, and the peak compressive force is appropriately scaled by the cross-sectional area to produce a compressive stress value. When compared to an Instron universal testing machine (UTM), the field measurement device exhibited a low bias induced by measurement hardware sampling limits. When a low-pass filter was applied to the Instron data to replicate the hardware properties of the field measurement device, good agreement was found for compressive force tests performed on laboratory ice spheres, and it was clear the device was capturing a relative measure of strength. The mean compressive stress for natural hail was similar to that of pure ice spheres, but individual thunderstorm events exhibited variability. Laboratory ice spheres also showed significant variability, which argues for large sample sizes when testing any material for impact resistance.

Full access
Rodger A. Brown
,
Vincent T. Wood
,
Randy M. Steadham
,
Robert R. Lee
,
Bradley A. Flickinger
, and
Dale Sirmans

Abstract

For the first time since the installation of the national network of Weather Surveillance Radar-1988 Doppler (WSR-88D), a new scanning strategy—Volume Coverage Pattern 12 (VCP 12)—has been added to the suite of scanning strategies. VCP 12 is a faster version of VCP 11 and has denser vertical sampling at lower elevation angles. This note discusses results of field tests in Oklahoma and Mississippi during 2001–03 that led to the decision to implement VCP 12. Output from meteorological algorithms for a test-bed radar using an experimental VCP were compared with output for a nearby operational WSR-88D using VCP 11 or 21. These comparisons were made for severe storms that were at comparable distances from both radars. Findings indicate that denser vertical sampling at lower elevation angles leads to earlier and longer algorithm identifications of storm cells and mesocyclones, especially those more distant from a radar.

Full access
Jung-Hoon Kim
,
Robert D. Sharman
,
Stanley G. Benjamin
,
John M. Brown
,
Sang-Hun Park
, and
Joseph B. Klemp

Abstract

Spurious mountain-wave features have been reported as false alarms of light-or-stronger numerical weather prediction (NWP)-based cruise level turbulence forecasts especially over the western mountainous region of North America. To reduce this problem, a hybrid sigma–pressure vertical coordinate system was implemented in NOAA’s operational Rapid Refresh model, version 4 (RAPv4), which has been running in parallel with the conventional terrain-following coordinate system of RAP version 3 (RAPv3). Direct comparison of vertical velocity |w| fields from the RAPv4 and RAPv3 models shows that the new RAPv4 model significantly reduces small-scale spurious vertical velocities induced by the conventional terrain-following coordinate system in the RAPv3. For aircraft-scale turbulence forecasts, |w| and |w|/Richardson number (|w|/Ri) derived from both the RAPv4 and RAPv3 models are converted into energy dissipation rate (EDR) estimates. Then, those EDR-scaled indices are evaluated using more than 1.2 million in situ EDR turbulence reports from commercial aircraft for 4 months (September–December 2017). Scores of the area under receiver operating characteristic curves for the |w|- and |w|/Ri-based EDR forecasts from the RAPv4 are 0.69 and 0.83, which is statistically significantly improved over the RAPv3 of 0.63 and 0.77, respectively. The new RAPv4 became operational on 12 July 2018 and provides better guidance for operational turbulence forecasting over North America.

Full access
Barbara G. Brown
,
Louisa B. Nance
,
Christopher L. Williams
,
Kathryn M. Newman
,
James L. Franklin
,
Edward N. Rappaport
,
Paul A. Kucera
, and
Robert L. Gall

Abstract

The Hurricane Forecast Improvement Project (HFIP; renamed the “Hurricane Forecast Improvement Program” in 2017) was established by the U.S. National Oceanic and Atmospheric Administration (NOAA) in 2007 with a goal of improving tropical cyclone (TC) track and intensity predictions. A major focus of HFIP has been to increase the quality of guidance products for these parameters that are available to forecasters at the National Weather Service National Hurricane Center (NWS/NHC). One HFIP effort involved the demonstration of an operational decision process, named Stream 1.5, in which promising experimental versions of numerical weather prediction models were selected for TC forecast guidance. The selection occurred every year from 2010 to 2014 in the period preceding the hurricane season (defined as August–October), and was based on an extensive verification exercise of retrospective TC forecasts from candidate experimental models run over previous hurricane seasons. As part of this process, user-responsive verification questions were identified via discussions between NHC staff and forecast verification experts, with additional questions considered each year. A suite of statistically meaningful verification approaches consisting of traditional and innovative methods was developed to respond to these questions. Two examples of the application of the Stream 1.5 evaluations are presented, and the benefits of this approach are discussed. These benefits include the ability to provide information to forecasters and others that is relevant for their decision-making processes, via the selection of models that meet forecast quality standards and are meaningful for demonstration to forecasters in the subsequent hurricane season; clarification of user-responsive strengths and weaknesses of the selected models; and identification of paths to model improvement.

Significance Statement

The Hurricane Forecast Improvement Project (HFIP) tropical cyclone (TC) forecast evaluation effort led to innovations in TC predictions as well as new capabilities to provide more meaningful and comprehensive information about model performance to forecast users. Such an effort—to clearly specify the needs of forecasters and clarify how forecast improvements should be measured in a “user-oriented” framework—is rare. This project provides a template for one approach to achieving that goal.

Open access
EXECUTIVE COMMITTEE2
,
James F. Kimpel
,
Robert J. Serafin
,
George L. Frederick Jr.
,
Eugene M. Rasmusson
,
Otis B. Brown
,
Mary M. Glackin
,
Kenneth C. Spengler
, and
Ronald D. McPherson
Full access