Definition of the mean environmental steering flow for TCM-90 tropical cyclones

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by  Bohner, Richard H.;Elsberry, Russell L.

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11.TITLE(IncludeSecurityClassification)
DefinitionofMeanEnvironmentalSteeringFlowforTCM-90TropicalCyclones
12.PERSONALAUTHOR(S) Bohner,RichardH.,Jr.
13a.TYPEOFREPORT 13b.TIMECOVERED 14 DATEOFREPORT(year,month,day) 15.PAGECOUNT
Master'sThesis From To 1992,September 91
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17.COSATICODES 18 SUBJECTTERMS(continueonreverseifnecessaryandidentifybyblocknumber)
FIELD GROUP SUBGROUP limitedregion/globalanalysis, meanenvironmental^ow, TCM-90, tropicalcyclonemotion,
wavenumberbandpassfiltering
19.ABSTRACT(continueonreverseifnecessaryandidentifybyblocknumber)
AdefinitionfortheenvironmentalsteeringflowinthevicinityoftheTCM-90tropicalcyclonesissoughtbybandpassfilteringtheNaval
OperationalGlobalAtmosphericPredictionSystemdeep-layermeanu-andv-velocityandgeopotentialheightfields. One-dimensionalandtwo-
dimensionalFourierdecompositionsinalimitedregion(120deg.long) andinaglobalregionarecomparedwithsixwavenumberbandpassfilters
(1-6,1-9,...,1-21). Themeasureofgoodnessoftheenvironmentalsteeringflowinterpolatedtothestormpositionwastodeterminetheminimum
standarddeviationsofthepropagationvector(definedasdifferencebetweenstormmotionandthesteeringestimate) forallsixstormsandthe
ensemble. Thebestresultswerefoundforeitherthelimitedregionandglobalone-dimensionalFourieranalysesoftheuandvwindfieldswitha
bandpassfilterthatincludedonlywavenumbers1-15. ThesixTCM-90tropicalcyclonesweresubsequentlyanalyzedusingthisdefinitionofthe
steeringflowtoestimatethepropagationvectorsandtoexaminethelinearshearandrelativevorticitygradientsoftheenvironmentalflow.
Exceptforearlystagesofstormsinlowlatitudes,thebandpassfilteredanalysesprovidedsteeringvectorsconsistentwiththechanging
translationdirections. However,thetranslationspeedstendedtoexceedthestormmotionandleadtomorewestwardpropagationvectorsthan
expected. Thesepropagationvectorstendedtobealmostperpendiculartotheabsolutevorticitygradientvector.
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Definition ofthe Mean Environmental SteeringFlow forTCM-90 Tropical Cyclones
by
Richard H. Bonner, Jr.
Lieutenant Commander, United States Navy
B.S., United States Naval Academy, Annapolis, Maryland, 1982
Submitted in partial fulfillment
ofthe requirements for the degree of
MASTER OF SCIENCE IN Meteorolgy and Physical Oceanography
from the
NAVALPOSTGRADUATE SCHOOL
September, 1992
ABSTRACT
A definition for the environmental steering flow in the vicinity of
the TCM-90 tropical cyclones is sought by low-pass filtering the Naval
Operational Global Atmospheric Prediction System deep-layer mean u- and v-
velocity and geopotential height fields. One-dimensional and two-
dimensional Fourier decompositions in a limited region (120° long) and in
a global region are compared with six wavenumber low-pass filters (1-6,1-
9,..., 1-21) The measure of goodness of the environmental steering flow
.
interpolated to the storm position was to determine the minimum standard
deviations of the propagation vector (defined as difference between storm
motion and the steering estimate) for all six storms and the ensemble.
The best results were found for either the limited region and global one-
dimensional Fourier analyses of the u and v wind fields with a low-pass
1-15.
filter that included only wavenumbers The six TCM-90 tropical
cyclones were subsequently analyzed using this definition of the steering
flow to estimate the propagation vectors and to examine the linear shear
and relative vorticity gradients of the environmental flow. Except for
early stages of storms in low latitudes, the low-pass filtered analyses
provided steering vectors consistent with the changing translation
directions. However, the translation speeds tended to exceed the storm
motion and lead to more westward propagation vectors than expected. These
propagation vectors tended to be almost perpendicular to the absolute
vorticity gradient vector.
in
.
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TABLE OP CONTENTS
I. INTRODUCTION 1
A. BACKGROUND 1
B. THE THREE-COMPONENT PARTITION 5
C. OBJECTIVES 6
II. PROGRAM DEVELOPMENT 7
A. MOTIVATION 7
B. ERRICO DETRENDING PROCEDURE 8
C. FILTER PROGRAM DESCRIPTION 9
D. WAVENUMBER FILTERING 10
III. DATA ANALYSIS 16
...
A. INTERPOLATION OF FILTERED FIELDS TO STORM POSITION 16
B. SELECTION OF OPTIMUM ANALYSIS METHOD AND FILTER 19
IV. STEERING FLOWS FOR TCM-9 STORMS 25
1. Typhoon Winona 25
2 Typhoon Yancy 32
.
3. Typhoon Zola 41
4 Typhoon Dot 47
5 Typhoon Ed 54
.
6. Supertyphoon Flo 61
V. CONCLUSIONS AND RECOMMENDATIONS 70
APPENDIX A: DISCUSSION ON FFT2D/FFT2B SUBROUTINES 73
IV
LIST OF REFERENCES 76
INITIAL DISTRIBUTION LIST 78
LIST OF TABLES
Table I. PARAMETERS CALCULATED FOR EACH BEST TRACK STORM POSITION. 17
Table II. DATE AND TIME (00 UTC OR 12 UTC) OF ANALYSES OF TCM-90
TROPICAL CYCLONES 18
Table III. MEANS AND STANDARD DEVIATION VALUES FOR X-COMPONENT (TOP
NUMBER) Y-COMPONENT (BOTTOM NUMBER) AND MAGNITUDE OF
, ,
PROPAGATION VECTORS DERIVED FOR 16 MAP TIMES DURING TYPHOON
ED 21
Table IV. NUMERICAL SUMMARY OF TCM-9 TROPICAL CYCLONE ANALYSIS BY
WAVENUMBER LOW-PASS FILTER AND ANALYSIS METHOD 23
Table V. SUMMARY OF TCM-90 TROPICAL CYCLONE ANALYSIS OF U, V WINDS
VS GEOSTROPHIC WINDS, ANALYSIS METHOD, AND WAVENUMBER LOW-PASS
FILTER BY STORM 24