Search Results

You are looking at 1 - 10 of 24 items for

  • Author or Editor: Robert W. Burpee x
  • Refine by Access: All Content x
Clear All Modify Search
Robert W. Burpee

Abstract

Precipitating cumulus clouds occur regularly in the afternoon over the south Florida peninsula during summer months. A day without significant rainfall or radar echoes is rare. This paper discusses one such day, 23 July 1987, during which a dry, stable airmass covered the Florida peninsula. Nonprecipitating shallow cumulus formed in a few areas, but there were not any deep, precipitating cumulus clouds over land. The thermodynamic characteristics of the airmass are described and the synoptic-scale patterns that produced the airmass are presented.

Full access
Robert W. Burpee

Abstract

No abstract available

Full access
Robert W. Burpee

Abstract

Computations of peninsula-scale convergence in southern Florida reveal that daily-averaged surface convergence on sea-breeze days with relatively little rainfall is larger than on days with widespread rain. This negative correlation between surface convergence and area-averaged rainfall occurs as a result of significantly less surface convergence in the late afternoon and early evening on those days with considerable rainfall. The decrease in sea-breeze convergence during the late afternoon of the days with extensive rainfall is apparently a consequence of the downdrafts and thunderstorm-generated circus cloud cover produced by the deep convection that forms in the sea-breeze convergence zones. Before the typical midafternoon maximum of deep convection on sea-breeze days, there is no significant difference between the surface convergence averaged for days with widespread rain and for days with little rain. Important differences are observed, however, in the middle troposphere, where the sea-breeze days with widespread rain are more moist and have cooler temperatures than the days with little or no rain. The observations suggest that both the magnitude and timing of the convective response to the sea-breeze forcing during the afternoon are very sensitive to the moisture amount and some-what less sensitive to the thermal stability in the midtroposphere.

Full access
Robert W. Burpee

Abstract

Sanders designed a barotropic tropical cyclone (TC) track prediction model for the North Atlantic TC basin that became known as the Sanders barotropic (SANBAR) model. It predicted the streamfunction of the deeplayer mean winds (tropical circulation vertically averaged from 1000 to 100 hPa) that represents the vertically averaged tropical circulations. Originally, the wind input for the operational objective analysis (OA) consisted of winds measured by radiosondes and 44 bogus winds provided by analysis at the National Hurricane Center (NHC), which corresponded to the vertically averaged flow over sparsely observed tropical, subtropical, and midlatitude oceanic regions. The model covered a fixed regional area and had a grid size of ~ 154 km. It estimated the initial storm motion solely on the basis of the large-scale flow from the OA, not taking into account the observed storm motion.

During 1970, the SANBAR model became the first dynamical TC track model to be run operationally at NHC. Track forecasts of SANBAR were verified from the 1971 TC season when track model verifications began at NHC until its retirement after the 1989 Atlantic TC season. The average annual SANBAR forecast track errors were verified relative to Climatology and Persistence (CLIPER), the standard no-skill track forecast. Comparison with CLIPER determines the skill of track forecast methods. Verifications are presented for two different versions of the SANBAR model system used operationally during 1973–84 and 1985–89. In homogeneous comparisons (i.e., includes only forecasts for the same initial times) for the former period, SANBAR's track forecasts were slightly better than CLIPER at 24–48-h forecast intervals; however, from 1985 to 1989 the average SANBAR track forecast errors from 24–72 h were ~10% more skillful than homogeneous CLIPER track forecasts.

Full access
Robert W. Burpee

Abstract

No Abstract available.

Full access
Robert W. Burpee

Abstract

No abstract available

Full access
Robert W. Burpee

Abstract

Routine perusal of surface maps covering tropical and subtropical regions frequently reveals the presence of large-scale patterns in the 24 h pressure tendency. Previous analyses of surface pressure, 1000 mb heights and 500 mb heights have determined that these oscillations, have a preferred frequency and are caused by a global-scale wave with a wavelength equal to the circumference of the earth and a period of about 5 days. In order to investigate this wave motion in more detail, the troughs of 60 waves were followed from eastern Africa to the western Caribbean, and both surface and upper air data were composited relative to the troughs. The surface pressure analysis shows that the wave is nearly in phase from 30°N to 30°S and that the minimum amplitude occurs near the equator. Upper air observations in the region from 10–30°N indicate that the wave features do not tilt significantly in the vertical from the surface to 70 mb. Although the amplitude of the waves in the surface pressure field is less than 1 mb throughout the tropics; and the horizontal scale is zonal wavenumber 1 or 2, the data show that the wave affects the occurrence of both precipitation and thunder.

Full access
Robert W. Burpee

Abstract

A compositing technique has been used to analyze the wind field of easterly waves in the GATE region of western Africa and the eastern Atlantic. The compositing analysis is similar to the method of Reed and Recker (1971), but this study includes variations of the waves as a function of latitude in addition to variations as a function of east–west wavelength and height. A wave composited for the summer of 1974 has been isolated from the mean flow and analyzed on constant pressure maps. From these analyses, kinematic vertical motion has been computed in the lower and middle troposphere. The results show that the pattern of vertical motion calculated from the compositing agrees quite well with satellite cloud patterns.

Full access
Robert W. Burpee

Abstract

This study uses both spectral and compositing analyses to determine the structure of North African easterly waves during the summers of 1968 and 1969. The average period and wavelength computed by the power-spectrum method are 4.5 days and 3800 km and for the compositing analysis 3.8 days and 3100 km. Although the period and wavelength of individual waves vary considerably, the spectral results are in qualitative agreement with the compositing results except in extreme northern Africa where eastward-moving disturbances of the same period affect the spectral computations. The maximum surface amplitudes of u, v, p and Td associated with the waves occur about 20N near the mean location of the east-west oriented region of minimum surface pressure. East of the Greenwich meridian the amplitude decreases and the wave motion is barely detectable with surface data near 25E. The compositing results show that the waves influence latitudes between 5 and 3ON and that wave features tilt from southwest to northeast. Both rainfall amount and thunderstorm activity are modulated by the passage of the waves with the rainfall maxima about 50% greater than the corresponding minima. Upper air calculations show that the vertical structure of the waves varies with the mean zonal wind in such a way that the meridional wind patterns tilt in the opposite direction to the mean zonal shear.

Full access
Frederick Sanders and Robert W. Burpee

Abstract

The barotropic prediction model, applied in a way appropriate to the character of tropical circulations and of the information available to describe them, is found to be capable of providing a basis for a significant advance of the state of the art of hurricane track forecasting in the range from 24–72 hr in regions of relatively dense rawinsonde data coverage. The distinctive features of the technique are application of the barotropic equation to tropospheric mean data computed from information at 10 constant-pressure levels, prognostic use of a stream function derived from direct analysis of the mean wind field, and numerical calculation over a grid with relatively small mesh length, without separation of the tropical vortex from the residual flow.

A series of test forecasts for hurricanes Donna 1960, Carla 1961, and Flora 1963 illustrates the performance of the model in dealing with storms characterized by a wide variety of behavior. The most prominent failure, a premature forecast of the recurvature of Donna, is found to be attributable to the baroclinic filling of a trough off the east coast of the United States.

Full access