Chris Davis (NCAR) Collaborators: Lance Bosart Ron McTaggart-Cowan Andy Heymsfield
Benjamin J. Moore, Lance F. Bosart , and Daniel Keyser
description
Transcript of Benjamin J. Moore, Lance F. Bosart , and Daniel Keyser
Synoptic environments associated with predecessor rain events in advance of
landfalling tropical cyclones
Benjamin J. Moore, Lance F. Bosart, and Daniel KeyserDepartment of Atmospheric and Environmental Sciences, University at
Albany/SUNY, Albany, NY 12222
Michael L. Jurewicz, Sr.NOAA/NWS, Binghamton, NY
Northeast Regional Operational Workshop XI, Albany, NY
5 Nov 2009
NOAA/CSTAR Grant NA07NWS4680001
Outline
• Motivation• Definition of a PRE• Data and methodology• TC-relative composite analysis• PREs associated with TC Frances (2004) and TC
Rita (2005)• Concluding remarks
Motivation
• Identify preferential dynamic and thermodynamic configurations for PREs to improve forecasts
• Establish physical mechanisms accounting for different spatial and temporal characteristics of PREs
TC Frances12Z 8 Sep 2004
TC Rita06Z 25 Sep 2005
66 66PRE
PRE
Motivation
Definition of a PRE
• Defined as distinct mesoscale regions of heavy rainfall [~100 mm (24 h)−1] ~1000 km downstream of landfalling and recurving TCs (Cote 2007)
• Develop as a poleward stream of deep moisture from the TC interacts with a baroclinic environment
Conceptual model from Bosart and Carr (1978) for a rain event associated with TC Agnes (1972)
Data and Methodology
• PREs for 1988–2008 identified using:• National base reflectivity radar mosaics (cases during
1995–2008)• 1° GFS analyses and 2.5° NCEP–NCAR reanalysis data • NCDC Hourly Precipitation Dataset• NPVU QPE • UPD
• PREs stratified by TC recurvature at time of PRE initiation
• Pre-recurvature – no component of TC motion vector in the positive x-direction• Post-recurvature – component of TC motion vector in
the positive x-direction
Data and Methodology
• TC-relative compositing:– 6 hourly 2.5° NCEP–NCAR grids for PRE cases were
shifted so that TCs were located at same position– PRE cases were stratified into pre- and post-
recurvature categories and composited at time of initiation
– Cases which deviated significantly in synoptic environment were excluded
– Only one PRE from each parent TC was used in compositing
PREs 1988−2008
PRE-REC
URVATURE
POST-RECURVATURE
05
10152025303540
Num
ber o
f PRE
s
PRE-REC
URVATURE
POST-REC
URVATURE0
5
10
15
20
25
DURA
TIO
N (h
)
• 65 PREs associated with 37 TCs• Pre-recurvature category is
characterized by larger separation distance and longer duration
PRE-RECURVATURE POST-RECURVATURE300
500
700
900
1100
1300
1500
SEPA
RATI
ON
DIS
TAN
CE (k
m)
29
34
N=63
TC-Relative Composites
Pre-recurvature PREs Post-recurvature PREsN=12 N=13
kts
200 hPa heights (dam, black), winds (kts, barbs ≥40 kts), wind speed (kts, shaded ≥50 kts); 850 hPa relative vorticity (10−5 s−1, blue)
200 hPa
TC-Relative Composites
Pre-recurvature PREs Post-recurvature PREsN=12 N=13
mm
700 hPa heights (dam, black), 500-850 hPa layer-averaged wind (kts, barbs ≥10kts), total column precipitable water (mm, shaded)
700 hPa
TC-Relative Composites
Pre-recurvature PREs Post-recurvature PREsN=12 N=13
850 hPa heights (dam, black), Q-vectors (10 −11 K m −1 s −1), Q-vector convergence (10 −16 K m −2 s−1, shaded), potential temperature (K, red)
850 hPa
10 −16 K m −2 s −1
PRE associated with TC Rita 24–26 Sep 2005Pre-recurvature PRE
1200 UTC 24 Sep – 0000 UTC 26 Sep 2005: 200 hPa mean geopotential height (dam, black), wind speed (≥70 kts, red), and total precipitation (mm, shaded)
mm
00Z25 Sep
06Z19 Aug
03Z25 Sep
06Z25 Sep
12Z25 Sep
Source: NCAR case selection archive
Radar EvolutionWSR-88D base reflectivity
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
0600 UTC 25 Sep 2005
850 hPa 200 hPa
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
0600 UTC 25 Sep 2005
850 hPa Pre-recurvature composite
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−2 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
0600 UTC 25 Sep 2005
200 hPaPre-recurvature composite
1200 UTC 7 Sep – 0000 UTC 9 Sep 2004: 200 hPa mean geopotential height (dam, black), wind speed (≥70 kts, red), and total precipitation (mm, shaded)
mm
PRE associated with TC Frances 7–8 Sep 2004Post-recurvature PRE
Radar Evolution
06Z8 Sep
12Z08 Sep
09Z8 Sep
15Z8 Sep
Source: NCAR case selection archive
WSR-88D base reflectivity
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
1200 UTC 8 Sep 2004
850 hPa 200 hPa
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−1 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
1200 UTC 8 Sep 2004
Post-recurvature composite850 hPa
Synoptic Environment
mm850 hPa heights (dam, black),
Q-vectors (10−11 K m−2 s−1), potential temperature (K, red), total column precipitable water (mm, shaded)
kts
200 hPa heights (dam, black), winds (kts, barbs), wind speed (kts, shaded);
850 hPa relative vorticity (10−5 s−1, blue)
1200 UTC 8 Sep 2004
Post-recurvature composite 200 hPa
PREs in context of extreme rain producing MCSs
Frontal type flash flood pattern from Maddox et al. (1979)
PRE Composite
Surface 1000 hPa winds (m s−1), heights (dam), θe (K)
66
LH
5 m s−1
Concluding RemarksKey features of composites– Pre-recurature PREs• PRE develops in equatorward entrance region of
anticyclonically curved upper-level jet streak
• Upper-level flow characterized by ridge overlying the TC and broad, positively tilted trough well upstream and poleward of TC
• Low-level anticyclone downstream of TC facilitates poleward flow towards zonally oriented baroclinic zone frontogenetical forcing, moisture transport from the TC
Concluding RemarksKey features of composites– Post-recurvature• PRE develops in equatorward entrance region of
anticyclonically curved upper-level jet streak
• TC much closer to axis of upstream trough and jet streak
• TC circulation impinges upon low-level baroclinic zone
• Frontogenetical forcing at the terminus of low-level jet associated with TC circulation and downstream anticyclone
• Tropical moisture plume extends poleward and eastward along a SW−NE oriented baroclinic zone
Case studies– Rita (2005): Pre-recurvature PRE
• PRE was quasi-stationary and long-lived• PRE developed along zonal baroclinic zone in equatorward
entrance region of upper-level jet• Anticyclone over the eastern U.S. aided in the transport of TC
moisture to region of lift– Frances (2004): Post-recurvature PRE
• PRE was small-scale and quasi-stationary• PRE developed on the warm side of baroclinic zone in
equatorward entrance region of upper-level• Strong low-level flow associated with TC and downstream ridge
was associated with moisture transport and warm air advection
Concluding Remarks