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Hypothesis PresentationsEvaluation criteria:1.) Scientific merit: Are the scientific arguments well-
reasoned, clearly explained, and sensible from the standpoint of physical processes and previous research?
2.) Proposed method: Is it sound and well defended? Will the investigator actually be able to do what they propose (is the project “tractable”) in the time available?
3.) Value of work: To what extent will the proposed research benefit society, and potentially lead to larger implications and impacts, if successfully completed?
4.) Q&A: How well did PI respond to any audience questions/concerns?
Diabatic Rossby Waves as a Model for Convectively-
Coupled African
Easterly Waves
James RussellMEA716
African Easterly Waves (AEWs) and Diabatic Rossby Waves (DRWs)
DRWs1. Mid-latitude vortices/waves driven by
convective growth/propagation mechanism2. Convection ahead of PV maxima generates
low-level PV 3. New PV ultimately propagates and grows
wave
Fig: 2PVU iso-surface and 850hPa winds associated with a DRW (Winterstorm Lothar) approaching Europe.
Hypothesis:The DRW mechanism advects the AEW through convective generation of PV ahead of the AEW trough
Original AEW PV Anomalies
AEWs as DRWsConvection and diabatic heating generated ahead of AEW trough
Wave advected westward by convective generation of PV
New Convectively Generated PV
Case Study: AEW that led to Hurricane Earl19 - 26 Aug 2010
WRF Specs:Shin-Hong PBLTiedtke CumulusWSM-6 MicrophysicsNoah LSMRRTM and Dudhia Radiation
36km
12km4km
Method/Simulation
Sensitivity Study: Decrease moisture in IC’s and BC’s.Analysis: Examine PV budget.Expectation: Diabatic PV tendency weaker in sensitivity test.
TroughRidge
Wave moves westward with
time
Observed: ERA-Interim 650hPa Meridional Winds (m/s, color-shaded) & TRMM 3B42 Rainrate (mm/hr, contoured) averaged between 5-20N
Simulated: WRF 650hPa Meridional Winds (m/s color-shaded) & WRF Total Rainrate (mm/hr, contoured) averaged between 5-20N
RecapH
ypot
hesi
s The DRW mechanism has some role to play in the growth and propagation of AEWs.
Met
hod WRF control
simulation to resolve convection.Sensitivity study reducing moisture. Ex
pect
atio
n Diabatic PV tendency lower/ insignificant in sensitivity study when compared to control.
Questions?
AFRICAN EASTERLY WAVES (AEWS) Westward propagating synoptic scale disturbances
Precursor to many Atlantic hurricanes
Heavily modulates West African weather
Unsolved problem in atmospheric sciences
AEW EVOLUTION Barotropic‐baroclinic instabilities
Mesoscale convective triggers (latent heating)
Upstream Energy Dispersion
Orographic Forcing
OROGRAPHIC FORCING Lin et al., 2005
23/34 (’90‐’01) tropical cyclones began as MCCs near the Ethiopian Highlands (EH)
Concluded that pre‐Hurricane Alberto AEW linked with orographic forcing
Convection generated over EH and disturbance forms in the lee of EH
HYPOTHESIS African easterly waves can exist independent of orography African Easterly Jet exists due to the surface meridional temperature gradient, not orography
Hydrodynamic instability has been shown to be a major contributor to AEW (citations)
EXPERIMENTAL DESIGNHypothesis: African easterly waves can exist independent of orography
Simulations CONTROL: Default simulation with
original, observed orography
FLAT: Experimental simulation with completely flattened orography, all else same as CONTROL
Physics options (for both simulations) Kain‐Fritsch CP, WRF single moment
6‐class MP, and YSU PBL schemes
EXPERIMENTAL DESIGNHypothesis: African easterly waves can exist independent of orography
Analysis Longitude‐Time (Hovmoller) diagrams to analyze wave structure
Eddy kinetic energy (EKE) maps
EKE budget analysis
African Easterly Jet (AEJ) profile
PREDICTIONSHypothesis: African easterly waves can exist independent of orography
In the FLAT simulation, we will see less AEW activity in regions adjacent to and westward of mountainous regions, such as in Algeria (5 ◦E, 25 ◦N)
Everywhere else, in the FLAT simulation, other mechanisms with continue to produce AEW similarly to the CONTROL, but with minor differences
PRELIMINARY RESULTSHypothesis: African easterly waves can exist independent of orography
Wave Comparison
V windsFilteredV winds
PRELIMINARY RESULTSHypothesis: African easterly waves can exist independent of orography
Wave Comparison
V windsFilteredV winds
PRELIMINARY RESULTSHypothesis: African easterly waves can exist independent of orography
Wave Comparison
FilteredV winds
FilteredV winds
PRELIMINARY RESULTSHypothesis: African easterly waves can exist independent of orography
Mean AEJ profile (lines) and mean EKE (shaded)
CONTROL
FLAT
FURTHER EXPERIMENTATIONHypothesis: African easterly waves can exist independent of orography
Is 50 km grid spacing too coarse? AEWs are synoptic scale disturbances (L ≈ 1000 km) but could significant orographic effects that are perhaps unresolved by 50 km grid spacing affect AEW development?
Experiment Reduce grid spacing from 50 km to 36 km Add 12 km nested grids to current domain Examine smaller window of time to reduce computational expense
FURTHER EXPERIMENTATIONHypothesis: African easterly waves can exist independent of orography
Various orography removal Perhaps only some regions
contribute AEW development, or perhaps there is some dependency on orographic height
Experiments Reduce heights in various
locations, such as the Ethiopian highlands
Reduce heights and slopes by 50% and increase by 150% and examine AEW development
FURTHER EXPERIMENTATIONHypothesis: African easterly waves can exist independent of orography
Eddy kinetic energy (EKE) budget How does orography effect barotropic, baroclinic, and upstream dispersion EKE tendencies?
Experiment Examine different EKE tendency contributions in the different proposed experiments
The fields needed for this are already in the model output, so this is just a call for further analysis, not further simulations
QUESTIONS? ReferencesLin, Y.‐L., K. E. Robertson, and C. M. Hill, 2005: Origin and Propagation of a Disturbance Associated with an African Easterly Wave as a Precursor of Hurricane Alberto (2000). Mon. Wea. Rev., 133, 3276‐3298.
Motivation: Low instability convection poses a high risk to public safety!
Scientific Question: Are low instability convective environments sensitive to microphysics parameterization scheme choices?
Hypothesis: There is a microphysics parameterization scheme that is most favorable for simulating low instability convective environments.WSM6 = 31.8 mm Lin = 35.8 mm
mm
Predictive skill will improve by determining the most favorable microphysics scheme.
Better predictability means a reduction of public risk!
Real‐data case: February 18, 2009 Run a WRF ensemble of different microphysics parameterization schemes
Compare results to observations: Quantitative Precipitation Estimation Spatial coverage of precipitation Equitable Threat Score
Sensitivity of turbulent fluxes and precipitation pattern to terrain data
resolution in WRFMasih EghdamiMarch 15, 2016
Introduction
• Nastrom‐Gage (1985)
• Stronger precipitation has larger sensitivity and uncertainty. Smith et. al (2004)• Orographic clouds produce localized extreme values of rainfall that are associated
with natural hazards such as landslides, debris flows and flash floods. Nogueira et. al (2014)
• Deficiencies in the global angular momentum budgets. Kain et. al (2008)
Hypothesis
• If the terrain resolution is increased, turbulent fluxes also increase.
• How does the model know about the subgridscale topography statistics?
• Is there a scale invariance?
• In general, the total resolved plusparameterized variables in the modelshould be independent of theresolution.
• Accuracy of parameterizations can beused to improve the model.
‐5/3
‐3
Test and ComparisonStation Disdrometer Location Elevation (m)
P 02 University of North Carolina‐Asheville (UNCA) 646
P 03 Purchase Knob (Great Smoky Mountains) 1493
P 09 Haywood Community College 794
P 11 Mount Mitchell 1897
Rainfall data Wilson and Barros (2015)
Preliminary results
Arc Length scale
30 second 0.93 km
2 minutes 3.71 km
5 minutes 9.27 km
10 minutes 18.6 km
Resolution=12 km Resolution=3 km Resolution=1 km
May 12‐16, 2014 – (IPHEx) IntegratedPrecipitation and Hydrology Experiment
Res Do1 Do2 Do3
30 s 1.8151 2.3564 3.4586
10 min 0.5338 0.8012 1.0018
P2 – Valley (646 m)
Res Do1 Do2 Do3
30 s 0.5499 1.7269 4.3881
10 min 1.7133 1.5416 1.6015
P11 – Ridge (1493 m)
Not consistant
Understandingtheimportanceofincludingoceanicmesoscalecold‐coreandwarm‐coreeddiesintropicalcyclonesimulations
Motive: Improve hurricane simulations/forecasts by determining importance of inclusion of mesoscale eddies
Problems: Lack of ocean/atmosphere coupling leads to inaccurate estimations of tropical cyclone intensityUse of climatological profiles for SST does not take into account mesoscale eddiesMany variables: translation speed and thermocline depth!
Laura McGeeMEA 7163/15/2016
HurricaneKenneth(2005)
Pasch, Richard J. , 2006. Tropical Cyclone Report Hurricane Kenneth, 14‐30 September 2005: National Hurricane Center. Available from http://www.nhc.noaa.gov/data/tcr/EP112005_Kenneth.pdf [Access 15 March 2016].
Hypothesis: Using a climatological profile, we will see a radical difference in Kenneth’s intensity—namely, intensity will not decrease. Inclusion of mesoscale eddies in models of hurricanes with slower translation speeds (such as Hurricane Kenneth) will more accurately represent real‐life hurricane intensity.
WRF‐ARWRunGFS Analysis DataDomain: 10 to 20N, 112 to 140W12 km grid spacing3D PWP ocean model activatedNamelist options:
Microphysics scheme: WRF SM6CSLong‐ and short‐wave physics : RRTMGSurface layer physics: MM5LSM: NOAHPBL: YSUCumulus Parameterization: Tiedtke (old)
WorthinessHurricane translation speed can change due to unforeseen factorsSlow translation speed over colder/warmer waters can decrease/increase hurricane intensityKnowing intensity = vital for evacuation, damage estimates, insurance purposes
Overview
• High-shear, low-CAPE* (HSLC) convection represents a serious forecasting problem over portions of the U.S.
Sherburn et al. (2016, in prep.)CAPE
0-6
km s
hear
Tornado Watch Missed Tornadoes
Dean and Schneider (2008, 2012)
Tornado Watch False Alarms
Dean et al. (2009) *SBCAPE ≤ 500 J kg-1
MUCAPE ≤ 1000 J kg-1
0-6 km SVM ≥ 18 m s-1
Overview
• HSLC environments encompass a large fraction of EF1 or greater tornadoes and significant wind reports in the cool season and overnight
Sherburn et al. (2016, in prep.)
Overview
• Until recently, research on HSLC environments has primarily been limited to case studies, with little investigation into dynamics governing the evolution and strength of HSLC convection
Sherburn et al. (2016, in prep.)
• Typically associated with strong synoptic forcing for ascent, intense flow throughout the depth of the troposphere, and moist lower troposphere
• Instability, albeit limited, tends to be focused over the lowest 3 km, while low-level shear tends to be stronger in severe events
Initial Question
How is severe convection initiated and maintained in an environment with limited buoyancy?
Surface θ’ (K)
Sherburn and Parker (2015, AMS Mesoscale Conference)
Reflectivity (dBZ)
Homogeneous environment
Two approaches…
Heterogeneous environment
Reflectivity (dBZ) Courtesy: Jessica King
Initial Question
How is severe convection initiated and maintained in an environment with limited buoyancy?
Homogeneous environment
Two approaches…
Heterogeneous environment
• Initialized by a single sounding
• Initialized with cold block to mimic cold front or, perhaps more appropriately, a gust front
• i.e., need some artificial forcing to initiate convection
• Convection eventually organizes along this initial cold block or a separate, storm-generated cold pool
• Realistic?
• Pre-convective environment modulated only by convection itself
• Full four-dimensional heterogeneity
• Convection develops “naturally”, with a realistic treatment of synoptic and mesoscale influences
• Recent work has highlighted importance of low-level θe advection and potential instability in rapid environmental evolution preceding convection
• Pre-convective environment evolves due to convection and by continued synoptic and mesoscale influences
My Research Question(s)
How much of the pre-convective environmental evolution is attributable to the convection itself, and is a single-sounding approach ever sufficient to determine potential severity of an
HSLC environment?
Hypotheses: A relatively small percentage of environmental evolution is explained by the influence of the convection itself.
However, a single-sounding approach will be sufficient to provide a reasonable depiction of convection evolution and its potential severity (measured by lowest model level wind speeds and low-
level rotation tracks), assuming it is representative of the convection’s immediate environment (i.e., within ~1 hour of
convection’s arrival at a given location).
Methodology
Heterogeneous: WRF• 12-km parent domain, 4-km and 1.333-km
one-way nests
• Tiedtke CP scheme on 12-km domain, explicit otherwise
• WSM6 microphysics scheme (consistent with work by Jessica King; may experiment with others)
• YSU PBL scheme (consistent with results from Cohen et al. 2015)
• NARR initial/boundary conditions
• Plan on at least two simulations• February 26, 2008• February 24-25, 2011• Represent cases where potential instability and low-
level advection were especially important, respectively (Jessica King)
Homogeneous: CM1• 250-m grid spacing
• Previous experiments have revealed substantial changes in strength of convection between 500-m and 250-m; relatively small change between 250-m and 125-m runs
• Initialized with single sounding taken from WRF simulations 120, 90, 60, and 30 minutes prior to arrival of convection
• NSSL double-moment microphysics scheme (may change to keep consistent with WRF)
• No surface fluxes, radiation, Coriolis
• Initialized with line of warm bubbles (may use cold block if warm bubbles proves insufficient)
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