improving upper-level performance in amps: longwave radiation
DESCRIPTION
Improving Upper-Level Performance in AMPS: Longwave Radiation. Jordan G. Powers, Steven M. Cavallo, and Kevin W. Manning. • Motivation for AMPS Investigation – Examination of WRF simulations of Atlantic basin hurricanes: T biases at upper levels found - PowerPoint PPT PresentationTRANSCRIPT
Jordan G. Powers, Steven M. Cavallo, and Kevin W. Manning
• Motivation for AMPS Investigation
– Examination of WRF simulations of Atlantic basin hurricanes: T biases at upper levels found
– Model top cooling from longwave (LW)processes (RRTM LW scheme) significantly higher than observation
• AMPS Testing
– Analysis of summer and winter periods to assess extent of problem
– Test simulations with RRTM LW schememodifications performed
Upper-level T Biases: WRF 2009 Atlantic Basin Hurricane Forecasts
(WRF) (v. Time) WRF–GFS Analysis (v. Time)
Upper-level cooling over time
Output from fcst hr 6
-10K max
Note: SLP RMSEs also decrease with modified scheme.
– 1 week period / Fcsts every 12 hrs / 6-hr fcsts – MLS= Mid-Latitude Summer / TROP= Tropical
W/o H2O adj: Refined buffer layer and T profile
Full mods: H2O adjustment (std profile) in buffer layer (to avoid excessive
MT moisture)
Bias reductionsfrom mods
RRTM LW Scheme Modification— Atlantic Basin Experiments
Heating Rates Heating Rate Differences (Modified – Unmodified RRTM)
Configuration of AMPS for Investigation / Testing
Domains: 45-km / 15-km
Test fcsts: 6-hr
IC/BCs: GFS
Test periods:
Summer January 1-7, 2010
Winter July 1-7, 2009
15 km
45 km
RRTM LW Scheme: Original Model Top Treatment
• Buffer layer from model top (MT) to top of atmosphere (TOA)
– Extra computational level in LW scheme only: No new model η-level
• Layer properties
– T isothermal: MT value
– qv constant: MT value
– O3 set to .6O3 MT value
RRTM LW Modifications
• Computational layer refined: Multiple levels to TOA added
– p= 2.5 mb
– Extra levels in scheme, not η-levels (no significant extra run time)
• Improved T representation
– Temps at new levels related to average T profile (using T at MT)
• Excessive moisture prevented: Layer H2O= 5 ppmv
• O3 interpolated from table
WRF Water Vapor Issue
• Potential for Excessive Moisture at High Levels: Affects LW Flux Calculations
– <Jan 2010: No H2O vapor fields above 100 mb in GFS files
– WPS assumption (where nec’y): 5%≥ RH ≥1% for 300–50 mb
– Problem: Too moist in stratosphere
• Standard profile value: 5 ppmv
• WRF-Var minimum qv: qv= 1e-6 kg/kg (o(5 ppmv))
(if qv < 1e-6 kg/kg)
WRF: Atlantic Basin Tests
AMPS Upper-Level Water Vapor
Summer Testing
Top η1/2
Level(12 mb)
Domainavg qv
Winter Testing
SAW= Sub-Arctic Winter SAS= Sub-Arctic Summer
WRF-Var min qv 1e-6
Sounding maxima
Analysis of AMPS Heating Rates: Original RRTM LW
Winter Summer
Heating Rates
HeatingRateBias
SAW= Sub-Arctic Winter SAS= Sub-Arctic SummerMLW= Mid-Latitude Winter MLS= Mid-Latitude Summer
Net= ∂/∂t LW + ∂/∂t SW
SAS LW
AMPS–SAW AMPS–SAS
SAS SW
Cooling bias
Excessive LW
AMPS Differences from Standard Profiles and Single-Column (SC) Tests
Winter Summer
Summer SC SAS test: Problem in RRTM LW scheme
SAW Temps/SAS Temps: SC model run w/given temp profiles
Single column: SC version of RRTM (run from domain-avgd profile of T)
AMPS: Cooling biasSC SAS: Projected cooling bias at MT(excl. artifact)
for SC model for SC model
AMPS’s lesser cooling rate may reflect colder Antarctic stratosphere
SC top value: Artifact of extra level
: Extrapolated SC: Extrapolated SC
Analysis of AMPS Heating Rates: Modified RRTM LWWinter Summer
HeatingRates
Modified –Control
Control= Original RRTM LW Experiment= Modified RRTM LW
MT T 5 days: ~9 K
Max ~1.8K/d
Model Top Improvement: Summer ∂/∂t (LW) Control
∂/∂t (LW) New–Control
∂/∂t (LW) New
_6h (Total) New–Control
Mods reduce cooling and eliminateexcess qv
impacts
hr6 – hr0
∂/∂t (LW)= Instantaneous heating rates avg’d/fcst hr 6 ∂/∂t (Total)= hr6 – hr0 Level = η1/2
Mods reduce cooling bias
SummarySummary
• WRF MT cooling bias seen in Antarctic/AMPS application
– Summer signal
– Moderate compared to non-polar WRF applications
• AMPS upper-level H2O vapor
– Localized high qv biases near MT from soundings
– Large vapor amounts can influence LW calculations
• RRTM LW Mods: Decreased MT cooling & T errors in AMPSRRTM LW Mods: Decreased MT cooling & T errors in AMPS
– Mods reduce LW flux errors and excessive cooling
– Mods avoid LW errors due to areas of excessive qv at MT