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 scheme modifications 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 H 2 O adj: Refined buffer layer and T profile Full mods: H 2 O adjustment (std profile) in buffer layer (to avoid excessive MT moisture) Bias reductions from 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, 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 – q v constant: MT value – O 3 set to.6  O 3 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 H 2 O= 5 ppmv O 3 interpolated from table

WRF Water Vapor Issue Potential for Excessive Moisture at High Levels: Affects LW Flux Calculations – <Jan 2010: No H 2 O 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 q v : q v = 1e-6 kg/kg (o(5 ppmv)) (if q v < 1e-6 kg/kg) WRF: Atlantic Basin Tests

AMPS Upper-Level Water Vapor Summer Testing Top η 1/2 Level (  12 mb) Domain avg q v Winter Testing SAW= Sub-Arctic Winter SAS= Sub-Arctic Summer WRF-Var min q v 1e -6 Sounding maxima

Analysis of AMPS Heating Rates: Original RRTM LW WinterSummer Heating Rates Heating Rate Bias SAW= Sub-Arctic Winter SAS= Sub-Arctic Summer MLW= 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 WinterSummer 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 bias SC SAS: Projected cooling bias at MT (excl. artifact) for SC model AMPS’s lesser cooling rate may reflect colder Antarctic stratosphere SC top value: Artifact of extra level : Extrapolated SC

Analysis of AMPS Heating Rates: Modified RRTM LW WinterSummer Heating Rates 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 eliminate excess q v impacts  hr6 –  hr0 ∂  /∂t (LW)= Instantaneous heating rates avg’d/fcst hr 6 ∂  /∂t (Total)=  hr6 –  hr0 Level = η 1/2 Mods reduce cooling bias

Model Top Improvement: Winter ∂  /∂t (LW) Control ∂  /∂t (LW) New–Control ∂  /∂t (LW) New ∂  /∂t (Total) New–Control  hr6 –  hr0 ∂  /∂t (LW)= Instantaneous heating rates avg’d/fcst hr 6 ∂  /∂t (Total)=  hr6 –  hr0 Level = η 1/2 Mods reduce cooling

Summary WRF MT cooling bias seen in Antarctic/AMPS application – Summer signal – Moderate compared to non-polar WRF applications AMPS upper-level H 2 O vapor – Localized high q v biases near MT from soundings – Large vapor amounts can influence LW calculations RRTM LW Mods: Decreased MT cooling & T errors in AMPS RRTM 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 q v at MT