JOURNAL

OF GEOPHYSICALRESEARCH,

VOL. 98, NO. D7, PAGES 13,063-13,070, JULY 20, 1993

Intraseasonal Variability of Katabatic Wind Over East Antarctica
and Planetary Flow Regime in the Southern Hemisphere
TETSUZO YASUNARI AND SATOSHI KODAMA
Institute of Geoscience, University of Tsukuba, Tsukuba, Ibaraki, JapanThe Intraseasonal variation (30- to 50-day period) of katabatic wind has been found at Mizuho
plateau, East Antarctica, as a predominant mode of the subseasonaltime scale variability. The
atmosphericcirculation in the southernmiddle and polar latitudes associatedwith this fluctuation of
katabatic wind has been deduced by using the NMC gridded 500-mbar zonal wind and geopotential
height field. The axisymmetric circulation pattern to Antarctica is noticeable in the anomalouszonal
wind and height field. That is, the strong(weak) katabatic wind phasecorrespondsto the shallowerandbroadened(deepenedand narrowed) troposphericcircumpolar vortex with weaker (stronger) westerlies over the surroundingoceans. These results strongly suggestthat the intraseasonal variation of
katabatic wind regime over East Antarctica is part of the modulation of planetary flow regime andmeridional circulation in the southern middle and high latitudes, i.e., part of the index cycle of thesouthern hemisphere.

1.

INTRODUCTION

The katabatic wind regime over Antarctica has been
manifested as a huge drainage flow along the slope surface of
the ice sheet, maintained primarily by negative buoyancy of
the air near the surface, which is induced by strong radiational cooling at and near the ice sheet surface. A characteristic nature of this wind regime noted by many observations
is its steadiness throughout the year [e.g., Schwerdtfeger,1984], particularly in winter. The model studies by Ball
[1960], Parish [1984], and others have established the theories of steady katabatic wind as a sloped boundary layer
wind regime, where the Coriolis and frictional forces arebalanced with the buoyancy force.
The recent model-based studies [Egger, 1985; Parish andBromwich, 1991] have suggested that the katabatic windregime should be part of the large-scale tropospheric meridional

circulation

overand around

Antarctica.

ParishandBromwich [1991], for example, showedin a mesoscalemodelwith the realistic orography of Antarctica that the circumpolar vortex in the upper troposphere develops rapidly inresponseto the cooling of the ice slopes and development of
the katabatic wind regime. However, Egger [1985] andJames [1987] also pointed out that the circumpolar vortex
induced by the katabatic flow regime near the surface
counteracts the katabatic flow and even destroyed it throughthe intensified pressure gradient force of the upper level.
Egger [1992] further found the two steady state solutions of
the circulation regime, one where a realistic circulation
prevails under the substantial momentum transport by thecircumpolar westerly waves and another one with strong
upper level polar vortex but no surface easterlies (i.e.,
katabatic wind).
On the other hand, recent observational studies havepresented ample evidences of large variance of intraseasonal(20- to 60-day period) time scale in the planetary scale
circulation regime in the middle and polar latitudes of thesouthern hemisphere [e.g., Graham, 1989; Mo and Ghil,
1989; Shiotani, 1990; Kidson, 1991]. Shiotani [1990], forexample, showed a dominant mode of the north-south oscillation of zonal mean circulation in the middle through thepolar latitudes with the intraseasonal (30- to 40-day period)
time scale. Kidson [1991] deduced some dominant telecon-

nection patterns in the time-filtered 500-mbar height field,
which include the wave train patterns of wavenumber 3 or 4
and the zonally symmetric pattern involving the intensitychange of the circumpolar vortex.
These theoretical and observational studies have urged us
to investigate the observed temporal variability of the katabatic wind and its association with the planetary scale
circulation in the southern hemisphere. This paper willaddress this issue particularly relevant to the intraseasonalvariability, by analyzing the time series of the katabatic windover East Antarctica and the hemispheric gridded wind andpressure field data.

2.

DATA

Paper number 92JD02084.

The wind and temperature data obtained at the 30-m
level of the meteorological tower of the Mizuho Station(70ø42'S, 44ø20'E, 2230 m above sea level (asl), which islocated at the slope of East Antarctica under the typical cold
katabatic climate zone [Dalrymple, 1966], were used as ameasure of the katabatic wind. The general feature of
katabatic wind over this region is described by Inoue et al.
[1983]. The data of about 2 years from February 23, 1979, toJanuary 7, 1981, were used, which were obtained as part of
the Polar Meteorology Experiment in the south polar region(POLEX-South), Japan. The data obtained originally forevery 1 min were edited to the daily mean values for thepresent analysis. The radiosonde observations made once or
twice a week at the Mizuho Station [Kawaguchi et al., 1985]
were also used additionally to examine the wind and temperature profile. The National Meteorological Center (NMC)
global analysis data in 5ø x 5ølatitude/longitude grids at 0000
GMT were adopted for the analysis of the hemispheric0148-0227/93/92JD-02084505.00

circulation

Copyright 1993 by the American Geophysical Union.

13,063field.

13,064YASUNARI AND KODAMA.' KATABATIC WIND AND PLANETARY FLOW

-10.0

-21.2

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-43.7

-55.0

(•s)

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18.0

12.0

6.0

0.0

w

27O.O

180.0
90.0

0.0 M A M J I A S O N D I
1979

F M AM I J A S ON D J

ß 1980•. 1981Fig. 1. Daily time series of (a) temperature, (b) wind speed, and (c) wind direction at Mizuho Station, East
Antarctica, during the period from March 1, 1979, to January 31, 1981.

3.

SPECTRA AND COSPECTRA OF WIND AND TEMPERATURE
AT MIZUHOSTATION

Figure 1 shows the time series of daily mean wind speed,
temperature, and wind direction for the analysis period of
684 days (from February 23, 1979, to January 7, 1981). The
wind speed shows the steadinessthrough the period with themeanspeedof about15m s-1 , buta weakseasonal
cycleisalso apparent with the minima in midsummer (January). The
wind direction shows the strong steadinessthrough the yearwith the direction of around 90ø (i.e., from the east), indicating the characteristic of the katabatic wind at the slope of
the ice sheet. The temperature shows, by contrast, a large
seasonal cycle with the coreless winter [van Loon, 1967]. In
addition, both the wind speed and the temperature series
show shorter time scale fluctuation with a few days to 1- or
2-month periods.
Spectral analysis of the maximum entropy method (MEM)
was applied to these time series of wind speed and airtemperature to see more quantitatively the dominant periodicities. The annual cycles (represented by the 1-year plus
half-year harmonics) were subtracted from the original series
before applying the spectral analysis. Figure 2 shows thepower spectra of wind speed and temperature. A remarkablefeature that appeared commonly in the two diagrams is a

predominantpeak in the intraseasonaltime scalewithin a 30to 60-day period, though the maximum power of the twoseries appears in a slightly different period range from eachother, i.e., the 30- to 40-day period in the wind speedbut 50to 60-day period in the temperature. There seems to beanother peak of about a 10-day period in the temperature,
but no correspondingpeak is apparent in the wind speed.
Figure 3 shows the two components of the cross spectra
between wind speed and temperature. The cospectrum(Figure 3a) shows one isolated positive peak at 30- to 40-day
period, implying the existence of the in-phase component of
the wind-temperature fluctuation of this period range. The
quadrature spectrum (Figure 3b) shows a predominant pos-

itive peak at 40: to 50-day period, which implies that aquarter-cycle phase difference between the temperature andthe wind speed is prominent in this period range.
To examine

the seasonal and interannual

modulationof

intraseasonal variability, time series of wind speed andtemperature were filtered for the 30- to 60-day period range.
The butterworth filter [Murakami, 1979] was adopted todeduce the filtered series with the maximum response of
40-day period and a half-time response of the 30-day and60-day period, respectively. The seriesof wind speedclearlyshowsa predominancyof this time scalethrough most of theYASUNARI AND KODAMA: KATABATIC WIND AND PLANETARY FLOW

analysisperiod but with relatively small amplitudesin spring(Septemberand October). The seriesof temperature showsa
significant seasonal modulation, i.e., large amplitudes in
winter half years (March to September)but small amplitudes
in summer half years. It seemsnot easy to deduce a simple
phase relation between the temperature and the wind speed
series,but nearly in-phaserelation is apparentthroughmostof the analysisperiod except March through July 1979. This
result suggeststhat the variation of temperature of thisperiod range is generally related to the large-scalefeatures of
the Antarctic circulation, rather than to the local or regional
effect (e.g., downslope advection) of the katabatic wind, inwhich the wind speedis expectedto be negatively correlated
to the temperature anomaly. This feature will further be

13,065(nVa)""o
40.0

22.5

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-12.5

-30.0 I......

i OOO

PERIOD(DAY)discussed later.
(m/s)*'C

4.

VERTICALSTRUCTURES OF WIND

AND TEMPERATURE

70.0

FIELD OF THE INTRASEASONAL TIME SCALE

By utilizing the filtered time series of wind speed (Figure4), we identified the strong (and weak) katabatic wind phases
for the intraseasonaltime scale, irrespective of the seasons.
The radiosonde data at Mizuho Station are, then, categorized to the strong, weak, or moderate phases. Unfortunately, as the number of radiosonde observations (about 60
times during the analysis period of the 2 years) were notsufficientfor producing the compositewind and temperature

50.O

30.0

I0.0

-1o.o I

1o

1oo

1ooo

PERIOD(DAY)POWER(-c)**o
400.0(a) TEMPERA•........

,........

,

Fig. 3. Two components of cross spectra between temperature
and wind speed at Mizuho Station. (a) Cospectrum and (b) quadrature spectrum.

I

300.0

200.0

0.0

10

100

1000

PERIOD(DAY)windis very weak(around5 m s-i) above800m fromthe

POWER((m/.)"*i)
400.0

surface. The wind direction is concentrated to NE (45ø) to E........

(90ø) in the katabatic wind layer and around E (90ø) in theupper layer up to 5000 m asl. In the weak phase, by contrast,
no (strong) katabatic wind layer is seen in the lower layer,
and the wind speedincreaseswith height up to about 3500 m
with nearly the constant direction from W (270ø). These
contrastive features between the strong and the weak windphase are more or less common in other strong and weakwind cases, which roughly correspond to the maximum andthe minimum wind speedphasesshown in Figure 4. That is,in the strong wind phase, the katabatic wind layer with adepth of 200-400 m is prominent with persistent easterly

300.0

200.0

o.o •

profiles; typical examples for the strong and weak katabatic
wind phase specified from Figure 4 is shown here. Figure 5
shows an example of the temperature and wind field profile
for the strong phase (April 7, 1980) and the weak phase(April 28, 1980). In the strong case the temperature is
generally high compared to the weak phase, except thenear-surface layer, where strong surface inversion exists.
The strong wind layer (i.e., the katabatic wind layer) in thestrong phase has a depth of about 400-500 m with a maximum at 200 m above the surface (about 2200 m asl), but the,o,oo
PERIOD(DAY)Fig. 2. Power spectra of (a) temperature and (b) wind speedat
Mizuho Station for the series shown in Figure 1. The seasonalcycle
is prefiltered.

windof morethan10m s-1. In themiddletroposphere,theweak northeasterly wind prevails. In the weak wind phase,
the westerly wind prevails throughout the tropospherewith
increasingwind speedwith height. The temperature profileshows systematic higher values in the strong phase than in13,066YASUNARI AND KODAMA.' KATABATIC WIND AND PLANETARY FLOW

(m/s)
4

3
2

0

0

Z

-2

-3
-4

i

-5

A

:

M

•

J

e

J

',

A

I

S

I

O

I

N

I

I

J

I

F

I

M

I

I

A

M

I

J

I

J

I

A

I

•

'

S 'O

•

' N ' D

I

J1980

1979

Fig. 4.

DBand-passfilteredtime series(with periodbandof 30 to 60 days)of wind speed(solidcurve) and temperature(dashed curve) at Mizuho Station.

the weak phase, though there seems to be no significant
difference of the relative profile or lapse rate pattern. In
some casesthe inversion near the surface is strongerin thestrongphase than in the weak phase (e.g., Figure 5), becauseof stronger advection of colder air from the interior of the
Antarctic plateau. In this case the negative correlation,rather than the positive correlation, between the wind speed
and the temperature becomes apparent, e.g., in MarchthroughJuly 1979.Thus the relation betweenthe wind speed
and the temperature is variable dependingupon the strengthof the downslope advection, though the large-scale effectseemsto be dominant, as shownin Figure 4. The associationof the vertical profiles over Mizuho Station with the hemispheric flow regime in the southern polar latitudes will be
discussed

later.

a.s.L (m)(a)

5.

COMPOSITES OF PLANETARY FLOW REGIME

To deduce

the association

betweenthe katabatic

windvariability and the planetary flow regime, the hemisphericgeopotential and wind field are composited in reference tothe strong and weak phases of katabatic wind shown in
Figure 4. Before making composites, we produced thefiltered geopotential and wind field by operating the same
filter as adopted for the Mizuho Station to the original grid
point data. Figure 6 showsthe compositegeopotentialanomaly field at 500 mbar for (Figure 6a) strong and (Figure 6b)
weak phases,which approximately showsa zonally symmetric structure of the anomaly field with positive (negative)
anomaly over Antarctica and negative (positive) anomaly
over the surroundingoceansduring the strong(weak) phase.

a.s.L(m)(b)

a.sd.(m)

(c)

42OO

-35.0

-30.0

-25.0

Temperature
CC)

-20.0

0.0

$.0

10.0

15.0

20.0

WindSpeed
(m/s)

25.0

0.0

90.0

180.0

W'md
•on

270.0

MOO

(des.)

SampleofTheStrongPhase- (4/7,1980)

SampleofTheWeakPhase- (4/28,1980)
Fig. 5.

Vertical structureof (a) temperature,(b) wind speed,and (c) wind directionfor a typical caseof strongand
weak katabatic wind at Mizuho Station (2230 m).

YASUNARI AND KODAMA: KATABATIC WIND AND PLANETARY FLOWThis anomaly pattern implies that the circumpolarvortex isweakened (intensified) and the meridional gradient of geopotential height is slackened (steepened) during the strong(weak) phases. Consistently with this anomaly pattern ofgeopotential field, the zonal wind anomaly at 500 mbar
(Figure 7) becomeseasterly (westerly) along the coastal zoneof Antarctica (about 50ø-60øS) during the strong (weak)phases. Mizuho plateau is located closely at one maximum
along East Antarctica in this anomaly zone. The equatorward of this anomaly zone, another zonally oriented zone ofzonal wind anomaly with the opposite sign is noted, whichsuggeststhe equatorward extent (poleward shrink) of thecircumpolar westerlies during the strong (weak) phases.
Figure 8 shows the composite wind vector anomaly at 500
mbar for the strong katabatic wind phase. As has beensuggestedin Figures 6 and 7, the anomalous anticyclonic
circulation is dominated over the circumpolar vortex zone

13,067
O'

s

90'W

90'

E

90'

E

180'

0'

Weak Pase0'

Strong
Phase

90'W

90'

w

90'

E

b
180'
180'

Fig. 7.

0'

90'

W

90'

E

t80'

Fig. 6. Anomalous geopotential height field at 500 mbar compositedfor (a) strongkatabatic wind and (b) weak katabatic wind of
the intraseasonaltime scale at Mizuho Station. Contours are 5 gpm(m) and negative values are shaded. Areas where the difference of
anomalies between the strong and the weak katabatic wind phaseshows 5% (or less) significant levels are dotted. The location ofMizuhoStationis indicated

with

"M."

Same as Figure 6 but for zonal wind. Contours are
0.5ms -1 .

centered over East Antarctica. It is interesting to note thatthe center of the anticyclonic circulation correspondswell tothe source region of mean katabatic wind regime locatedover the East Antarctic plateau. Another feature is a more orless zonally oriented zone of westerly anomalies along the
mid-latitudes (30ø-50øS), though it is less significant than the
anticyclonic anomaly zone over Antarctica.
To confirm the change of the real circulation over andaround Antarctica associated with the change of katabatic
wind regime, the total (i.e., nonfiltered) height field at 500
mbar was composited for the two phases. Figure 9 shows thetwo meridional sections of 500-mbar height along the longitude lines of 45øW to 135øE and 45øE to 135øW, the latternearly passesthrough the Mizuho Station at East Antarctica.
During the weak phase the deepened polar vortex and thesteeper meridional gradient of geopotential height along theoff-coastal zone of Antarctica are apparent, as has beensuggestedin the anomaly field. During the strong phase, bycontrast, the polar vortex is shallowed and broadened tosome extent. It is noteworthy to state that locally over East
Antarctica the meridional gradient is reversed in sign with a13,068

YASUNARI AND KODAMA: KATABATIC WIND AND PLANETARY FLOW
0u

(a)

•

Deep
Polar
Vortex •(b)

Show Polar
Vortex

90'W

10.

Om/s

Fig. 8. Difference of wind vector at 500 mbar composited forstrong and weak katabatic wind phases. Areas which are notsignificant(with 5% level) are shaded.

small maximum height immediately over the highestplateau
of Antarctica. This feature is par--ticularlyremarkable along
the line of 45øE to 135øW(Figure 9b). This implies that theso-called "polar anticyclone" near the Antarctic surface(a)500mbhe'i•ht
along
45W-13$E-a-Strng
5680-•-Weak

546O

524O

5O2O

480O

30

60

60

90

90

LatitudeAir(m)

500nabheightalong45E-135W
59O0=•-Strong
5680

StrongKatabaticPhase

Fig. 10. Schematicdiagramsof the upper troposphericcirculation over and around Antarctica for (a) weak katabatic wind phaseand (b) strong katabatic wind phase.

developseven to the midtroposphereduringthe strongphaseof katabatic wind regime.
The results obtained here agree well with the verticalprofile of temperature and wind field over Mizuho Station
described in section 4 (e.g., Figure 5). That is, the easterly
wind over Mizuho Station at 500 mbar in the strong windphase (Figure 5) is well consistent with the anticyclonic
circulation with the geostrophiceasterly over East Antarctica, as shownin Figure 8. The relatively high temperatureat
this level seemsto correspondto the relatively weak polar
vortex over Antarctica. The equatorward pressure gradientover Antarctica, associated with the formation of the nearsurface polar anticyclone centered over the East Antarctic
plateau, may be a direct causefor the strongkatabatic wind.
The composite hemisphericflow regime associatedwith
the strong (or weak) katabatic wind at Mizuho Stationstronglysuggeststhat theseanomalyflow regimesshouldbe
responsiblefor the anomalous state of katabatic wind not
only over the Mizuho plateau but also over the whole ofAntarctica, as shown in the nearly symmetric anomaly flow
pattern (e.g., Figures6 and 7) for the pole, or more exactly,
for the Antarctic plateau.

-•-Weak

6.

DISCUSSION

546O

524O

5020

4800

30

60

90

60

3O

LatitudeFig. 9. Cross sectionsof 500-mbar height compositedfor strong
and weak katabatic wind phasealong the longitudeline of (a) 45øWto 135øE and (b) 45øE to 135øW. The latitude of Mizuho Station isindicated with "M" in (b).

The intraseasonal variability of katabatic wind over Mizuho Stationwith about a 40-day period hasbeen revealedto
be closely related to the fluctuation of the hemisphericplanetary flow regime in the southern polar and middle
latitudes. The axisymmetric anomaly circulation patterns
deducedfrom the strong(or weak) katabatic wind phaseshas
led us to conclude that the change of katabatic wind regime
over Antarctica with this time scale is directly linked withthe changeof intensity of the upper troposphericcircumpolar vortex over Antarctica. The relation between the upper
troposphericflow regimeand the katabatic wind regime may
be schematicallysummarizedin Figure 10. It is clear that the

YASUNARI AND KODAMA: KATABATIC WIND AND PLANETARYFLOW

strong (weak) katabatic wind regime is associated with theshallow (deep) polar vortex with weaker (stronger) upper
westerlies. The supposed meridional circulation over thepolar latitudes may be strong (weak) during the strong(weak) katabatic phase. The warm (cold) anomaly in thetemperature field over Mizuho plateau during the strong(weak) katabatic phase may be fundamentallyinfluencedby
the intensity of the polar vortex. The role of adiabatic
heating due to the downward motion as part of the meridional circulation may be additional, but the cold air advection
from the upstreamsideof the ice plateau is, in some cases,
responsible for the lower temperature anomaly near thesurface during the stronger katabatic wind, as pointed out
earlier.

The implication of the anomalous flow patterns deduced
here associatedwith the fluctuation of katabatic wind regime
seemsto be very interesting. The previous theoretical studies [e.g., Egger, 1985; James, 1986, 1989; Parish andBromwich, 1991] showed that the katabatic wind regime over
Antarctica plays an important role in the generation of thecircumpolar vortex in the upper troposphere through thegeneration and transport of the vorticity in the strong easterly wind near the surface. The observational evidence thatin the seasonal cycle the katabatic wind regime is strongest
during winter when the circumpolar vortex is also strongest[Schwerdtfeger, 1984] seems to support this general idea.
James [1986] estimated that the vorticity generated by themeridional circulation induced by the katabatic wind iscomparable to that generated by the temperature gradient
between the Antarctic ice cap and the surroundingoceans.
On the other hand, most of these studies also noted thatthe katabatic wind regime decays quickly due to the opposing meridional pressure gradient force induced by the development of the circumpolar vortex unless the northwardtransport of cyclonic vorticity is out of the polar domain.
Recently, Egger [ 1992] further demonstrated in the axisymmetric model that two types of steady state be possible in the
Antarctic meridional circulation, one where strong katabatic
wind is coupled with weak upper level westerlies (or eveneasterlies) and another where weak or no katabatic wind iscoupled with strong upper level westerlies and deep circumpolar vortex. He noted that the selection of the state
depends on the strength of transport of westerly angularmomentum by eddies (i.e., wave and cyclone activity)
parameterized at the northern boundary of the model domain.

It is noteworthy to state that the two steady states notedby Egger [1992] seem to be comparable quite well to thestrong and weak katabatic wind phases in the present
analysiswith respect to the horizontal and vertical structureof wind, pressure, and temperature field. In fact, the slackened pressure gradient (or broadened and shallowed circumpolar vortex) in the strong katabatic wind phase may
correspond with the low-index type circulation over thesouthern high latitudes (40ø-60øS) around Antarctica withintensifiedplanetary wave activity. The deepenedcircumpolar vortex with stronger upper level westerlies over thesurrounding oceans, by contrast, correspond to the highindex type circulation with weakened planetary wave activity. The set of the anomalous 500-mbar height patterns
deducedhere (Figure 6) really seemsto be one (i.e., EOFs 5)of the dominant circulation patterns for the intraseasonal
time scale obtained by Kidson [1991], who has applied the

13,069empirical orthogonal function (EOF) analysis to the fiRered
500-mbar height field of 9 years (1980-1988) over the southern hemisphere. The similar pattern is also deduced by Mo
and Ghil [ 1989] as the first EOFs with a dominant periodicity
of $0 days.
This anomalous pattern should also be compared to themultiple equilibria of zonal mean flow of this time scale
noted by Yoden et al. [1987] and Shiotani [1990]. Though
they focused on the zonal mean statistics and their analysis
period is different from ours, the meridional structure ofzonal mean flow supposedfrom Figure 7 seems to be very
compatible with theirs. That is, the intraseasonalvariabilityof the katabatic wind regime described here is really part of
the hemisphericmodulation of the general circulation in thesouthern middle and high latitudes. In a sensethe katabatic
wind regime interacts with the planetary flow regime around
Antarctica, which result in the wax and wane of the cir-

cumpolar vortex or the "index cycle" of this time scale inthe southern hemisphere westerly flow. The mechanism
proposed by James [1989] that decaying mid-latitude cyclones induce net flux of cyclonic vorticity out of thecircumpolar vortex and maintain the katabatic wind seemsto
be very compatible with the present result. In the northernhemisphere, in contrast, the vacillation of the planetary
waves is an essential mechanism of the index cycle.
One problem may be what determines the time scale ofthis cycle. Is it an inherent mode of the southern higher
latitudes under the dynamic and thermodynamic constraintsof Antarctica and the surrounding oceans? Or otherwise,
does any external forcing from or interaction with theintraseasonal oscillation in the tropics [Madden and Julian,
1972] play an important role? Though there has been so far
little hemispheric scale evidences for the latter case [e.g.,
Shiotani, 1990; Kidson, 1991], some regional scale evidences[e.g., Yasunari, 1981a, b] suggest the possibility of thedirect interaction

betweenthe Antarctic

circulationand thetropical or monsoon circulation with this time scale.
7.

CONCLUSIONS

The fluctuation of katabatic wind regime with 30- to SO-day
period has been noted over Mizuho plateau, East Antarctica,
as a predominant mode in the intraseasonaltime scale. Thismode has been proved to be closely associated with thevariability of the hemisphericflow regime of the middle andupper troposphere in the southern middle and polar latitudes. The strong katabatic wind phase correspondsto theweak and shallow upper tropospheric circumpolar vortex
with weaker upper westerlies around it. The anticyclone
seems to be formed in the near-surface

level of the Antarctic

ice sheet at this phase. The weak katabatic wind phase, bycontrast, correspondsto the deep circumpolar vortex withstrongerwesterlies. The anomalouscirculation pattern at the
500-mbar level associatedwith this change of katabatic windregime approximately shows the axisymmetric (i.e., zonal
wavenumber zero) structure, suggestingthe close relation to
the multiple flow equilibria of the southernwesterlies [ Yoden
et al., 1987; Shiotani, 1990]. These observational results
have been found to be very compatible to the model resultsby Egger [ 1992] that two steady states of the katabatic windregime are possible in the axisymmetric flow over andaroundAntarctica

under the conditionof momentum

port by eddies at the northern boundary.

trans-

13,070
Further

YASUNARI AND KODAMA.'KATABATIC WIND AND PLANETARYFLOW
observational

as wellas theoreticalstudies haveto be made for understandingthe role of this variability in the
katabatic wind regime on the general circulation of thesouthern hemispheres.
Acknowledgments. We would like to thank Makoto Wada andTakashi Yamanouchi of National Institute of Polar Research (NIPR)
for supplyingus the edited meteorologicaldata obtained at Mizuho
Station during the POLEX-South. This paper is dedicatedto the late
Jiro Inoue of Disaster Prevention Research Institute of Kyoto
University, in memory of his extensive study on the climate ofMizuho plateau during the POLEX-South.
REFERENCES

Ball, F. K., Winds on the ice slope of Antarctica, in Proceedingsof
the Symposiumon Antarctic Meteorology, Melbourne, 1959, pp.
9-16, Pergamon, New York, 1960.
Dalrymple, P., A physical climatology of the Antarctic plateau, in
Studiesin Antarctic Meteorology, edited by M. J. Rubin, Antarct.
Res. Ser., 9, 195-231, 1966.

Egger, J., Slope winds and the axisymmetric circulation over
Antarctica, J. Atmos. Sci., 42, 1859-1867, 1985.
Egger, J., Topographic wave modification and the angular momentum balance of the Antarctic troposphere, J. Atmos. Sci., 49,
327-334, 1992.

Graham, N. E., Slowly evolving features in the winter Southern
Hemisphere 500 mb height field, Extended abstracts, in Third
International Conference on Southern Hemisphere Meteorology
and Oceanography, Buenos Aires, pp. 121-124, American Meteorological Society, Boston, Mass., 1989.
Inoue, J., H. Nishimura, and K. Satow, The climate of the interiorof Mizuho plateau, Mere. Natl. Inst. Polar Res., 29, 24-36, 1983.
James, I. N., Katabatic drainage flow over Antarctica and the polar
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S. Kodama and T. Yasunari, Institute of Geoscience, Universityof Tsukuba, Tsukuba, Ibaraki 305, Japan.

(Received January 7, 1992;
revised August 31, 1992;
accepted August 31, 1992.)