ESSL Nested Regional Climate Simulations with WRF Bill Kuo 1 C. Bruyere 1, J. Done 1, G. Holland 1, R. Leung 2, Y. Liu 1,3, S. Tulich 1, A. Suzuki 4 1. Mesoscale and Microscale Meteorology Division/NCAR, Boulder, CO 2. Pacific Northwest National Laboratory, Richland, Washington, Boulder, CO 3. Chinese Academy of Meteorological Science, Beijing 4. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA

ESSL Approach and Current Focus Approach: Nesting the NCAR Weather Research and Forecasting Model into global/climate models as a 2-way Nested Regional Climate Model (NRCM); –Stage 1: Downscaling over North America (done); –Stage 2: 2-way atmospheric scale interactions in the tropics (current); –Stage 3: NRCM in CAM/CCSM, with coupled ocean model; as a community facility (to come) –Goal: a full global Weather/Climate system (longer term). Current Focus: Tropical scale interactions: –Importance of mesoscale organization of convection and its related surface exchanges and radiative influences for forcing tropical modes; –tropical cyclone development and intensification, tropical waves, East Asia monsoons

ESSL WRF-NRCM Simulations Forcing data: –NCEP/NCAR Reanalysis –AMIP monthly SST data Model parameterization: –YSU boundary layer –Kain Fritsch convective parameterization “Bluevista run” – – 30 o S – 45 o N – 34 levels, 50hPa TOA “Columbia run” – – 45 o S – 45 o N – 50 levels, 10hPa TOA “2005 N. Atlantic run” 12 4

ESSL TC detection methodology New storm detection 1)Find SLP local minima 2)|Max relative vorticity| > 5x10 -5 s -1 3)Max wind speed > 18m/s 4)General wind pattern 5)Warm core Pre-existing storm continuity 1)Distinctive SLP local minima within 20 o of last storm location 2)Max wind speed > 18m/s 3)Warm core Updates storm location A storm satisfies continuity requirement for at least 48 hours Tropical Cyclone Check for overlaps in newly found storms and pre-existing storms Check for merging of separate storms “Eye-ball checks”

ESSL Columbia Bluevista Total TC count by year NRCM overproduced TCs (by about 25%) –SST setting? Model physics? Parameterization? Positive definite advection scheme?

ESSL “Bluevista run” ( , 30S-45N)

ESSL “Columbia run” ( , 45S-45N)

ESSL 10 year statistics

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ESSL Southern boundary extension Blueviesta Columbia Bluevista boundary

ESSL Atlantic and Northwest Pacific 2005 is a particularly active year for observed hurricanes over the Atlantic. But, NRCM under- predicts the number of storms.

ESSL “2005 North Atlantic nested run” May-Nov km domain forced at Northern and Southern boundaries 12km domain is nested over North Atlantic 2-way nesting

ESSL Non-nested 36km 18 storms (+1 from E.Pac) Nested 36km 25 storms (+1 from E.Pac) Nested 12km 29 storms (+1 from E.Pac) 2005 N.Atl 28 storms actual

ESSL Impact of nesting to larger environment 10 days running mean du/dz, 10 o – 20 o N average du/dz is more favorable in the nested run

ESSL Nested (1DOM) vs. Non-nested (Columbia 2005 May-Nov)

ESSL Summary The seasonal and geographical distribution of observed TC are well captured by NRCM in general. NRCM overproduces number of TC by about 25%: –TC overproduction was enhanced in Columbia run over the western north Pacific. –TC genesis over the tropical N. Atlantic was not well captured. Extending the southern boundary improved TC climatology in South Indian Ocean Nesting improved 2005 North Atlantic TC statistics and distribution. The vertical wind shear is more favorable for genesis with the nested simulations. Nesting changed TC counts over other regions, indicating that the impact of nesting can propagate to other regions.

ESSL The Problem: Tropical Modes Observed CCSM All tropical modes are poorly handled by current climate models. This impacts everything from tropical cyclones to ENSO and interactions with the extratropics. (Lin et al 2006)

ESSL NRCM vs. CLAUS (1997) CLAUS = Cloud Archive User Service, 3-hrly, Tb from multiple geostationary satellites

ESSL NRCM vs. CLAUS ( )

ESSL NRCM vs. CLAUS Kelvin-filtered data

ESSL NRCM vs. CLAUS Kelvin wave activity

ESSL Wave structures via lagged linear regression

ESSL Rain Climatology

ESSL Conclusions NRCM is fairly successful at capturing the propagation speeds and structures of convectively coupled Kelvin waves Variance is significantly under-predicted over S. America, Africa, and the Indian Ocean, perhaps stemming from poor precipitation climatology

ESSL The Great Red Spot: Excessive rainfall

ESSL OBS NRCM

ESSL Why NRCM produces excessive rainfall in the pacific ocean in 1997? In order to understand the problems associated with erroneous rainfall, we conducted a few sensitivity experiments: (1) Control run (2) Change Kain-Fritch cumulus scheme to Betts-Miller scheme. (3) Use explicit cloud microphysics without cumulus parameterization (4) Replace the 1997 SST by 1998 SST (5) Re-initialized NRCM at 1 May 1997 (cold start) With the cold start initial condition: (6) Add diurnal cycle into monthly SST (Zheng and Beljaars 2005) (7) Replace monthly SST by daily SST (interpolated from weekly SST) (8) Add diurnal cycle into daily SST

ESSL Control New I.C. Monthly SST+ Diurnal Daily SST+ Diurnal Daily SST 98 SST Explicit scheme GPCP

ESSL SST & Cu. Parameterization Changing precipitation parameterization schemes do not significantly affects the results. New initialization improves the results. But, model “lost the memory” of the new initial condition after about 1 month. SST has a profound influence on precipitation prediction: –98 SST produces better results than 97 SST –Adding diurnal cycle in itself does not produce improved results –Using daily SST with diurnal cycle helps the simulation. Issues with “prescribed SST”: –No “interaction” between atmosphere-ocean –No “cut-off” of solar radiation as a result of convection, and no “cooling-off” of SST –The warm (just by a few degree) 1997 SST keeps triggering convections

ESSL Next Phase of NRCM Experiments Nest a 60-km NRCM (one-way) within CCSM-3 T-85 climate simulations, with 21st century A2 scenario. Conduct 60-km runs: –5 ensemble members –Four 5-year period: , , , Conduct 20-km nested runs for North America, and North Atlantic (for hurricane simulations) Conduct 4-km nested runs over western U.S. One-way nesting will be the primary approach. Selected tests with 2-way nesting will be performed.

ESSL Next Phase of NRCM Experiments 60-km 20-km 4-km 20-km

ESSL OBSNRCMOBSNRCM OBS

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