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![Page 1: High-resolution Observations and Model Simulations of the Life Cycle of an Intense Mesoscale Snowband over the Northeastern United States Reporter: Prudence.](https://reader035.fdocuments.us/reader035/viewer/2022062517/56649ed95503460f94be706c/html5/thumbnails/1.jpg)
High-resolution Observations and Model Simulations of the Life Cycle
of an Intense Mesoscale Snowband over the Northeastern United States
Reporter: Prudence Yi-Yun Chien
Reference:
Novak, D. R., B. A. Colle, and S. E. Yuter, 2008: High-resolution Observations and Model Simulations of the Life Cycle of an Intense Mesoscale Snowband over the Northeastern United States. Mon. Wea. Rev., 136, 1433–1456.
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Outline
• Key words
• Introduction
• Datasets and methodology
• Case overview
• Band life cycle
• Moisture availability
• Summary and discussion
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Key words
yy
v
xy
u
yyx
v
xx
u
x
dt
dF D
1
2
2D form of frontogenesis equation (Miller, 1948)
Assess frontal forcing for ascent F2D > 0
3
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Key words
esgEPV Saturation equivalent potential vorticity (EPV)
θes surface slope > M surface slope
EPV<0Saturation environment
0
0
EPVfzgyMf
yMf
eses
es
1→2
Conditional Symmetric instability
CSI condition:
4
0
0
y
Mzes Conditional stable
Inertial stable, M = fy-ug
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Introduction
• Motivation:Advance cool-season QPF=> Structural and dynamical evolution of a cool-season mesoscale snowband
• Using high-resolution obs. & model
• Case period: 2002/12/25~ 2002/12/26
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Datasets and methodology
Dual-Doppler synthesis
1. Upper-air obs2. Doppler radar3. Wind profiler4. ground-based integrated
precipitable water vapor (IPW)5. Conventional surface obs6. Commercial aircraft
Observation
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MM5 V3.4
Cumulus Grell (1993)
Microphysics Dudhia (1989)
PBL MRF
IC NCEP - EDAS analysis (0000UTC 25 Dec)
BC NCEP – Eta forcast (0000UTC 25 Dec)
SST US Navy OTIS
Model configurations
31 sigma levels
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Case overview
• Synoptic-scale evolution
• Mesoscale evolution
• QPF
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Synoptic-scale evolution
500-hPa Φ(solid)
300-hPa wind (barb)
IR brightness temperature (shaded)
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Synoptic-scale evolution
isobars (solid)
isotherms (gray)
wind (barb) 10
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Mesoscale evolution
700-hPa Φ (thick solid)
F2D (thin solid)
reflectivity (shaded)
MM51800UTC 12/25
2760m2790m
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Mesoscale evolution
700-hPa θ (thick solid)
F2D (shaded)
wind (barb)
MM5 700-hPa Φ (thick solid)
F2D (thin solid)
reflectivity (shaded)
2100UTC 12/25
2700m 2760m
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Mesoscale evolution
700-hPa Φ (thick solid)
F2D (thin solid)
reflectivity (shaded)
MM50000UTC 12/26
2670m 2728m
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QPF 24-h accumulated precipitation (liquid equivalent)
1200UTC 12/25 ~ 1200UTC 12/26
Max = 76mm
Max = 53mm
underpredict~ 30%
Max = 59mm
underpredict~ 22%
Max = 46mm
underpredict~ 40%
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Band life cycle
• Band formation
• Band maturity
• Band dissipation
• Model time series
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Band formation
Conv.
R1
R2
Conv.
R1*
R2*
Conv.
R2Defm.
Conv.
R2*Defm.
1802UTC WSR-88D
1929UTC WSR-88D
1800UTC MM5
1930UTC MM5
F2D (shaded)
θ (solid)
Reflectivity, 1km (shaded)
wind, 3km (barb)
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Reflectivity (shaded)
Ascent (dot)
F2D (solid)
EPV (shaded) RH=100% (thick solid)
Negative η (dot)
θes (gray solid)
II & CICI
II & CI
snowfall
F2D max
Ascent max
1802UTC WSR-88D
1800UTC MM5
II
F2D max
Ascent max
II
CI:conditional instability
II: inertial instability
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Band maturity2101UTC WSR-88D 2100UTC MM5
2100UTC MM5
R2R2*
F2D (shaded)
θ (solid)
Reflectivity, 1km (shaded)
wind, 3km (barb)
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Reflectivity (shaded)
Ascent (dot)
F2D (solid)
EPV (shaded) RH=100% (thick solid)
Negative η (dot)
θes (gray solid)
2101UTC WSR-88D
2100UTC MM5
CI
Weak CSI
II
II
F2D max
Ascent max
F2D max
Ascent maxCS
Weak CSI
CS:conditional stability
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2300UTC MM52359UTC WSR-88D
2300UTC MM5
R2
R2*
Band dissipation
F2D (shaded)
θ (solid)
Reflectivity, 1km (shaded)
wind, 3km (barb)
20
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2300UTC MM5
2359UTC WSR-88D
Reflectivity (shaded)
Ascent (dot)
F2D (solid)
EPV (shaded) RH=100% (thick solid)
Negative η (dot)
θes (gray solid)
II
CI
II
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Model time series
Cross section A-B
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Moisture availability
Obs: IPW
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Band formation (1930UTC 12/25 MM5)
Band dissipation (2200UTC 12/25 MM5)
1930UTC
2200UTC
1930UTC
2200UTC
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2525
Compare QPF between 2100UTC and 2200UTC
Ascent profile Θe profile (QPF2200-QPF 2100)/QPF 2100
same -6%
same -23.5%
=> Changes in ascent dominated changes in moisture
MD
-0.14
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• Band evolution=> forcing, stability, and moisture
• Forcing (MM5 results)(1) Band formation deepening of a midlevel trough Increase in deformation, convergence, and frontogenesis
(2 )Band dissipation midlevel trough less defined, and frontogenesis weakened Conditional stability led to weak frontal circulation
Summary and discussion
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Summary and discussion
• StabilityConventional thinking: CI and SI increase => band formationThis study: CI occurred before band formation~1.5h band formation: CI decrease & F2D increase
• W max & F2D maxPrevious study: W max locate on the warm side of F2D max ~50-200km This study: W max and F2D max are nearly coincident
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Summary and discussion
• Moisturesource: Atlantic Ocean (band formation)change of ascent => change of moisture
• QPFMM5 underforecast ~30% max preci. (Δx=4km)axis of heaviest preci. ~50km to the SE of the observation locationHigher horizontal model resolution => improvement QPF much better improvement on F2D, stability, and moisture
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Thanks for your listening.&
Questions?
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Conditional instability (CI)
0
zes
0
zes
(Holton, 2004: An Introduction to Dynamic Meteorology (4 th Ed.), Fig9.10, p.294)
(2) Air parcel reach the LFC
0
zes
(1)
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Inertial instability (II)
Absolute momentum: M = fy - ug
(Holton, 2004: An Introduction to Dynamic Meteorology (4th Ed.), p.205)
In this study, set M = fy – u u=ug+u’
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Fig.7
Fig.8
Band formation
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