An Analysis of Central American Gyres
Philippe P. Papin, Kyle S. Griffin, Lance F. Bosart, Ryan D. Torn
Department of Atmospheric and Environmental Sciences: University at Albany/SUNY, Albany NY, 12222
Motivation
Fig 7. 850 hPa Circulation calculated
over a 500 km radius (shaded, s-1) and
850 hPa winds (vectors, between 1020 m s-1)
Fig 1b. Topography map of Central America.
September 2010 Gyre was well observed
Gyre produced series of major rainfall events in Mexico,
Jamaica, and the eastern United States
No previous gyre studies over Atlantic basin
Role of tropical cyclones (TCs)
1. TC Matthew as generator of Gyre
2. TC Nicole as product of Gyre
A 0000 UTC 27 Sep 2010
Gyre Definition
Northwest Pacific Basin
Low level cyclonic vortex on
order of 2500 km
Deep convection on
southern and eastern sides
of circulation
Mesoscale vorticies
downstream of convective
band (Possible TCs)
Multiweek lifespan
B 0000 UTC 29 Sep 2010
The Role of Gap Winds
Atlantic Basin (Sept. 2010)
Low Level cyclonic vortex
on order of 1000 km
Deep convection on
southern and eastern sides
of circulation
Mesoscale vorticies
downstream of convective
band (TC Nicole)
3-5 Day Lifespan
Fig 1. Track map of TCs Matthew and Nicole as well as a broad outline of the gyre circulation domain from 24-30 September.
Atlantic Basin
Fig 2. Meteosat 9 and GOES 12 Merged SAL Imagery For 0000 UTC 18 Sep 2010. Yellow to red shading indicates dry,
dusty lower tropospheric air, while white and gray areas represent cloud cover. Imagery courtesy of CIMSS
TC Julia
TC Igor
TC Matthew
TC Matthew
0000 UTC 24 Sep
0600 UTC 25 Sep
Fig 3. Precipitable water(shaded, every 2 mm), 850 hPa heights (white contours, 3dam), and 850 hPa winds (vectors).
A 0600 UTC 25 Sep
Anomalous easterly trade winds originate
in Saharan air layer (SAL) outbreak on
0000 UTC 18 September (Fig 2)
TCs Igor and Julia displace subtropical
ridge southward over Atlantic basin on
0000 UTC 20 September (Fig 3a)
850 hPa ridge rebuilds with enhanced
easterlies (Fig 3b)
Easterly flow (black arrow) maintained by
stronger than normal Bermuda high (Fig
4). Flow precedes easterly flow with TC
Matthew; aids in the gap flow through the
Chivela Pass (yellow arrow, Fig 3c).
B
0000 UTC 27 Sep
Anomalous Ridge
TC Matthew
Fig 4. 850 hPa geopotential height anomalies (shaded every
5m) along with anomalous winds (vectors) both averaged from
23-25 Sept.
Datasets
Enhancement of Azores-Bermuda high
necessary for gap winds in Chivela Pass
during summer.
Easterly flow on idealized NW/SE oriented
mountain chain will be diverted southward,
resulting in formation of low level jet
producing vorticity maxima that
propagates downstream.
Acts as source region for vorticity for
developing gyre
A
Synoptic-Scale Environment Sub Synoptic-Scale Analysis
SAL
0000 UTC 20 Sep
Calculating
Circulation makes it
easier to identify
center of gyre
rather than
following individual
vorticity lobes
Fig 5. Panel plots displaying NASA Merged IR BT data (shaded), and 850 hPa anomalous winds (vectors).
Gridded Climate Forecast System Reanalysis (CFSR)
NASA Merged IR Brightness Temperature (BT) data
0.5o resolution
Easterly winds shift northeasterly and
generate vorticity on windward side of Sierra
Madrea de Chiapas (Fig 6a,b)
Vorticity patch gets caught in westerly flow
over Pacific and loops back to Central
America(Fig 6 c,d,e,f). Gyre Forms at this
time
Vorticity patches continue to shift eastward
rounding the southern and eastern flanks of
gyre (Fig 6 g,h,i)
Furthest downstream vorticity patch
becomes TC Nicole (Fig 6j)
Gyre breaks down due to northerly midlatitude air (Cold Surge, Blue Arrow, Fig 6 i,j)
C
Synthesis and Conclusions
Anomalous easterly flow in Atlantic basin due to a SAL
outbreak and stronger than normal subtropical ridge lead
to a gap wind event through the Chivela Pass
Process generates vorticity that is shifts downstream of
mountains into east Pacific
Anomalous westerly flow in Pacific loops vorticity back to
Central America, resulting in a complete circulation
characteristic of a gyre.
TC Nicole results from
B
aggregation of vorticity on
periphery of gyre.
Breakdown of gyre occurs
with the introduction of
TC Matthew
TC Matthew
0000 UTC 25 Sep 2010
1200 UTC 24 Sep 2010
mid-latitude flow from
D
North America (cold surge)
L
TD Matthew
TC Matthew
1200 UTC 25 Sep 2010
E
0000 UTC 26 Sep 2010
F
1200 UTC 26 Sep 2010
G
0000 UTC 27 Sep 2010
H
Pacific Basin
September represents peak poleward progression of intertropical convergence zone (ITCZ) across the east Pacific.
Mean westerly low level flow between 5oN and 15oN in east
Pacific (Romero-Centeno et al. 2007).
Additional anomalous westerly flow on top of mean (Fig. 4,5)
Broad pattern of anomalous easterly winds over Gulf of
Mexico and Caribbean Sea combined with anomalous
westerly flow over east Pacific (Fig 5 A and B) leaves Central
America on cyclonic shear side of both wind anomalies.
Configuration favorable for cyclonic vorticity development.
Some
Questions
How Frequent are these
gyres?
Climatologically favored in
September?
Role of Kelvin waves
enhancing westerly flow
over east Pacific?
References and
Acknowledgements
1200 UTC 27 Sep 2010
I
0000 UTC 28 Sep 2010
J
TS Nicole
1200 UTC 28 Sep 2010
0000 UTC 29 Sep 2010
Fig 6. Panel 850-700 hPa layer relative vorticity (shaded, 10-5 s-1), terrain
(black contours, 500 m and up) and winds (vectors). The general
circulation of the gyre is highlighted by the black arrow and vorticity
maximums are circled in maroon.
 Lander, M. A., 1994: Description of a monsoon gyre
and its effects on the tropical cyclones in the western
north Pacific during August 1991. Wea. Forecasting, 9,
640–654.
 Mozer, J. B., J. A. Zehnder, 1996: Lee vorticity
Production by Large-Scale Tropical Mountain Ranges.
Part I: Eastern North Pacific Tropical Cyclogenesis. J.
Atmos. Sci., 53, 521–538.
 Romero-Centeno, R., J. Zavala-Hidalgo, G. B. Raga,
2007: Midsummer Gap Winds and Low-Level
Circulation over the Eastern Tropical Pacific. J. Climate,
20, 3768–3784.