determined by the radar altimeter. While the aircraft elevation varied, no
aircraft datum used had an elevation in excess of approximately 1700 m or less
than 250 m. Moreover, the majority of the data were clustered near 600 m and
1600 m. The horizontal distribution of aircraft data was relatively symmetric
about the storm center with all data points falling between 150-275 km radius.
(This does not include the core data used in the Frank (1984) composite.)
Surface ship and buoy data were at the 10 m level and were distributed
throughout most portions of the storm.

The horizontal distribution of the satellite wind vectors was rather
uniform, and all of the satellite winds used in this study were between
150-1000 km from the center of Frederic. Satellite wind vectors over land
were not used so that land induced-friction could not contaminate the wind
fields.

To aid in determining the heights of satellite wind vectors, radial and
tangential winds and inflow angles were calculated in storm relative
coordinates at each data point. The resulting values were divided into two
groups such that the winds and inflow angles obtained on 11 SEP (period 1)
were separated from those obtained from data on 12 SEP and early 13 SEP 1979
(period 2). This procedure was employed to minimize smoothing of small scale
or transient features in the wind field. It will become apparent after
further discussion below, that the preservation of the small scale kinematic
structure of Frederic is imperative to the successful determination of
satellite wind vector heights.

In addition to completing the above data analysis tasks, we have also
obtained the available stereo-imagery analyses and a copy of Powell's (1982)
boundary layer model. These are being used to assist in determining the

heights of the wind vectors (see below).


6. Publications
Frank, W.M. and E.B. Rodgers, 1984: Kinematic analysis of Hurricane Frederic
(1979) using satellite, aircraft and rawinsonde data. Final Report on

NASA Grant NAG 5-102.

7. References

Frank. W.M., 1984: A composite analysis of the core of a mature hurricane.
Mon. Wea. Rev., 112, 2401-2420.

Frank, W.M. and E.B. Rodgers, 1984: Kinematic analysis of Hurricane Frederic
(1979) using satellite, aircraft and rawinsonde data. Final Report on
NASA Grant NAG 5-102.

Powell, M.D., 1982: The transition of the Hurricane Frederic boundary-layer
wind field from the open Gulf of Mexico to landfall. Mon. Wea. Rev., 12,

1912-1932.


combined sources reflect the atmospheric conditions which were present over
the Gulf of Mexico and the contiguous land masses during the 41 hour period
beginning at approximately 1100 GMT on 11 SEP 1979 and terminating at 0400 GMT
13 SEP 1979. After eliminating those data. which were found to be inconsistent
with neighboring values, a final data set consisting of 64 rawinsonde
soundings, 177 aircraft data points (30-second averages), 237 satellite wind
vectors and 198 surface reports was compiled.

All of the data were plotted in storm relative coordinates. It was found
that the vertical and horizontal distribution of data from each individual
source was highly variable.

The rawinsonde data provided excellent vertical resolution, although the
horizontal distribution was rather poor. Eight data levels extending from the
surface to 500 mb were extracted from each rawinsonde sounding. The height of
each level was calculated using the hypsometric equation, and the 850 mb,

700 mb and 500 mb heights were compared to those plotted on conventional NMC
upper air charts. The depth of the Planetary Boundary Layer (PBL) was
estimated by examining the moisture and temperature profile of each sounding.
Since the rawinsondes were all launched from land stations, only data from
levels above the PBL were considered. The horizontal distribution of
rawinsonde data was asymmetric about the storm center with a minimum of data
coverage existing south-west of the storm center. All rawinsonde data used
fell between 300-1000 km radius from the storm's center.

The vertical resolution of the aircraft data was quite variable, while
the horizontal resolution was minimal. In regions where there were flights at
different levels, the resolution was naturally superior to those areas where

there was only data at a single level. The elevation of each data point was


4. Current Tasks

At the present time, subjective and objective analysis techniques are
being used to determine the heights of the satellite wind vectors. The first
step consists of objectively analyzing the tangential, radial and inflow wind
components separately in limited regions. This procedure is carried out
independently for the data from period 1 and period 2 using a Cressman
objective analysis scheme. The analysis grid measures 2730 km in the
north-south direction and 2030 km in the east-west direction, and the grid
spacing is 70 km. The purpose of this initial objective analysis is to smooth
data in local areas only.

The radius of influence, number of passes and the degree of smoothing
being employed in the initial objective analysis are somewhat unconventional.
Typically, the initial radius of influence chosen is approximately 1.6 to
1.8 x the grid spacing; however, an initial radius of 1.4 x the grid spacing
of 75 km is currently being employed. The number of passes used when
objectively analyzing data is normally a function of the initial radius of
influence of the data spacing. In the objective analysis scheme used in the
Penn State Mesoscale Model, for example, the initial radius of influence is
decreased by 30% for each scan until the radius is approximately equal to the
grid spacing. If this criteria were applied to the initial radius of = 105 km
used in this study, two passes would have been used. However, three and four
passes are being used in this study. Finally, no large-scale smoothing of the
objectively analyzed fields is employed in this study. The methodology
described above is designed to preserve small scale features in the radial,
tangential and inflow fields and to avoid smoothing over large areas.

In the second step used in determining the heights of the satellite wind

vectors, subjective analysis techniques are employed. In areas where there is


re

Annual Progress Report

NASA Grant NAG 5-398

Analysis of the Inflow Layer and Air-Sea Interactions
in Hurricane Frederic (1979)

William M. Frank
Principal Investigator

The Pennsylvania State University
Department of Meteorology
503 Walker Building
University Park, PA 16802

April 1985

soe REPRODUCED BY .
U.S. DEPARTMENT OF COMMERCE
NATIONAL TECHNICAL
INFORMATION SERVICE’
SPRINGFIELD, VA 22161


multiple-level data coverage, the satellite-wind vector heights are assigned
after comparing the radial and tangential winds and inflow angles of the
satellite wind vectors to the respective components from the other data
sources.

Because multiple-level data do not exist in many areas during either
period 1 or period 2, the heights of many satellite wind vectors cannot be
assigned directly. To alleviate this problem, satellite wind vector heights
from periods 1 and 2 are being combined to obtain a map of satellite wind
vector heights, for the 41-hour period beginning 1100 GMT on 11 SEP 1979 and
ending at 0400 GMT on 12 SEP 1979. We are assuming that although the wind
velocity of a given satellite wind vector may change from period 1 to period
2, the height of that same wind vector is less variable over the same time
period. That is, the heights of the satellite wind vectors are assumed to be

more conservative than the values of their wind components or inflow angles.

5. Remaining Work

The heights of all satellite-derived wind vectors will be estimated

within the near future. We will then proceed to the remaining tasks:

. Adjust the satellite winds to the primary analysis levels.

. Perform the integrated three-dimensional analysis of the inflow layer
kinematic fields using a cylindrical coordinate compositing
technique.

. Determine the inflow layer thermodynamic fields.

. Perform diagnostic budget analyses of moisture, sensible heat,
kinetic energy and momentum.

. Examine air-sea interactions, including surface stresses and heat and
moisture fluxes as budget residuals.

. Synthesize findings and publish the results.


1. Introduction

The goal of this project is to perform a detailed analysis of the inflow
layer of Hurricane Frederic for the period 11-12 SEP 1979. The core region
(0-150 km) has been analyzed by Frank (1984) using a combination of aircraft
and surface data. Powell (1982) composited surface data from the center to
about 800 km radius. Frank and Rodgers (1984) made a preliminary attempt to
integrate satellite-derived wind vectors and rawinsonde data with the other
data sets to obtain a continuous analysis from 0-800 km radius at three
levels, the surface, 560 m and 1600 m. While the results of the latter study
were promising, difficulties in assigning accurate heights to many of the
low-level satellite winds significantly degraded the accuracy of the results.
Assigning these wind vectors to either the 560 m level or the 1600 m level
proved unsatisfactory. Stereo imagery was available for a limited portion of
the analysis period, but the vast majority of the low-level satellite winds
were determined from single-satellite imagery.

The current study is attempting to overcome the problem of uncertain

heights of the satellite-winds by the following methodology:

(1) Vertical profiles of the tangential and radial winds are con-
structed wherever there are aircraft, surface and/or rawinsonde
data available at miltiple levels.

(2) The heights of satellite-derived wind vectors measured in the
vicinities of these independent vertical profiles are determined
by comparison with the profiles.

(3) Plan view analyses of the heights of the satellite-wind vectors
are obtained by subjective analysis of the results of (2).

Separate analyses are performed for 11 and 12 SEP 79.

(4) In the many regions where satellite-wind vectors represent


the only data source, the satellite~winds are adjusted to the 560 m
and 1600 m analysis levels. This is accomplished by using the
heights of the wind vectors (step 3) and observed vertical wind
variations from the nearest miltiple-data-level locations.

The central hypothesis being explored by the above analysis procedure is
that the heights of satellite winds and vertical wind shear patterns vary less
in the horizontal than to the winds themselves. If this were not true, then
all of the satellite wind vectors would be of little or no value since the
significant vertical shear of the radial wind in the inflow layer would result

in large inaccuracies in estimates of radial flow.

2. Objectives

The specific objectives of this study are to:

* Determine the effective heights of the satellite wind vectors.

. Integrate satellite, aircraft, rawinsonde and surface wind
measurements into a three dimensional analysis of the storm inflow
layer over water.

. Construct similar analyses of the thermodynamic fields in the
inflow layer.

. Perform diagnostic budget analyses of moisture, sensible heat,
kinetic energy and momentum in the inflow layer.

. Examine air-sea interactions from residuals in the budget analyses.

3. Significant Accomplishments
During the first year of the project, the primary achievement was the
completion of the task of data processing. The data set consists of

rawinsonde, aircraft, surface and satellite wind vector data. These four