Mesoscale weather prediction with the RUC hybrid isentropic-sigma

Mesoscale weather prediction with the RUC hybrid isentropic-sigma coordinate model and data assimilation system Stan Benjamin NOAA Forecast System Lab Boulder, Colorado Stan. Benjamin@noaa. gov http: //ruc. fsl. noaa. gov Rainer Bleck - Los Alamos John M. Brown - NOAA/FSL Kevin Brundage “ Dezso Devenyi “ Georg Grell “ Dongsoo Kim “ Geoff Manikin - NCEP/EMC Barry Schwartz - NOAA/FSL Tanya Smirnova “ Tracy Lorraine Smith “ Steve Weygandt “ Symposium - 50 th Anniversary - Operational NWP 15 June 2004

Rapid Update Cycle An unusual branch of the operational NWP family genealogy - Use of a quasiisentropic vertical coordinate for model prediction and data assimilation - Numerical weather prediction and data assimilation on a sub 12 h cycle (currently 1 h) 2

~1985 • FAA-sponsored Aviation Weather Forecasting Task Force • Recommendations: • Promote additional automated aircraft reports from commercial aircraft • Develop high-frequency NWP system • NMC (now NCEP) / PROFS (now NOAA-FSL) agreement on development of ‘high-frequency’ NWP system (Ron Mc. Pherson, Tom Schlatter, Sandy Mac. Donald) • Assimilation of anticipated increase of hourly 3 -d observations • wind profilers, commercial aircraft, satellite, radar, surface 3

Choices for vertical coordinate for atmospheric prediction models • Height • Pressure • Entropy Potential temperature - = T (1000/p)R/Cp Isentropic weather maps - commonly used in US in late 1930 s Rossby et al. 1937 - plagued by reported Montgomery stream function - inaccurate integration of hydrostatic 4 equation

Modeling efforts with pure isentropic vertical coordinates • Eliassen and Raustein – 1968 But what to do about that lower boundary condition … • Bleck – 1974, 1977 (carrying sfc as prognostic variable) Now how to resolve the planetary boundary layer … Hybrid isentropic-sigma models • Bleck – 1978 • Deaven – 1976 • Gall – 1972 • Uccellini et al. – 1979 • Johnson et al. - 1993 • Konor and Arakawa – 1997. . . 5

1990 FSL/Bleck model using Uccellini-type hybrid - model Bleck and Benjamin – 1993 - MWR Benj, Grell, Brown, Smirnova, Bleck, 2004 – MWR Bleck and Boudra – 1981 - hybrid-isopycnic model Generalized vertical coordinate 6

Montevideo south Vertical section through HYCOM solution. Heavy black lines: coordinate surfaces. Shaded contours: potential density Hybrid (isopycnic-sigma) Ocean Community Model – HYCOM - U. Miami, Los Alamos Natl. Lab - from Rainer Bleck 7

Why even try to use a quasi-Lagrangian vertical coordinate? • Adaptive higher vertical resolution - vertical gradient of wind, moisture, chemical species … • Less cross-coordinate vertical transport 3 -d fluid motion resolved largely by 2 -d transport - Less non-physical diffusion, less aphysical source of entropy in numerical model (Bleck…, Johnson 1997) 8

Quasi-horizontal / Cartesian vs. functional spatial definitions Isobaric Isentropic 9

Cross section A Vertical coordinate definition - examples: Sigma-pressure p(k), ptop (fixed) (+psfc) (adaptive) p(i, j, k) Generalized - pmin(k), v- ref(k) (fixed) (+psfc , v) (adaptive) p(i, j, k) RUC generalized vertical coordinate - configured as a hybrid isentropic-sigma coordinate Reference v values (220 -500 K) pre-assigned to each of RUC levels. 10

Continuity equation (inviscid, adiabatic conditions in generalized coordinate s) Pressure Isentropic ~0 0 Mass conv/div 0 ~0 11

12 h forecast 24 h forecast RUC 20 km model forecast - initial conditions – 12 z 4 February 2001 36 h forecast Tropopause level (h. Pa) - defined as potential vorticity (PV) unit = 2 12

Potential vorticity Relative humidity N S Vertical velocity (x 10 b/s) N S Vertical cross-sections from RUC 36 -h forecasts - valid 00 z 6 Feb 2001 13

RUC model with a) - coord (control) b) coord (fixed) much better moist reversibility w/ - model PDF – grid pts at lev 40 e conservation tests Histogram of e - e (proxy) (K) MWR article – Feb 2004 -Mesoscale wx pred W/ RUC hybrid model -Benj, Grell, Brown, Smirnova, Bleck 24 h forecast Init 00 z 8 Feb 2001 14

OI, 3 dvar techniques in - coordinate developed for RUC analysis Advantages of Coordinates for Data Assimilation Analysis - adaptive 3 -d correlation structures and analysis increments, esp. near baroclinic zones, vertical spreading = f( ) - improved coherence of observations near fronts for QC Forecast Model - reduced vertical flux through coordinate surfaces, leading to reduced vertical dispersion -- much of vertical motion implicit in 2 -d horiz. advection - conservation of potential vorticity - reduced spin-up problems (Johnson et al. 93 MWR) 15

~1985 • FAA-sponsored Aviation Weather Forecasting Task Force • Recommendations: • Promote additional automated aircraft reports from commercial aircraft • Develop high-frequency NWP system • NMC (now NCEP) / PROFS (now NOAA-FSL) agreement on development of ‘high-frequency’ NWP system (Ron Mc. Pherson, Tom Schlatter, Sandy Mac. Donald) • Assimilation of anticipated increase of hourly 3 -d observations • wind profilers, commercial aircraft, satellite, radar, surface 16

The 1 -h Version of the Rapid Update Cycle at NCEP 17 NCEP model hierarchy – RUC (1 h frequency) Eta (6 h) Global (6 h)

Model/ Assim system Horizontal resolution No. Assimilation Implement at vert frequency NMC/NCEP levels RUC 1 60 km 25 3 h 1994 RUC 2 40 km 40 1 h 1998 Added • state-of-art model physics – convection, mixed-phase cloud, land-sfc • assimilation of surface obs • hourly cycling of • 5 -type hydrometeor cloud variables, • land-surface variables (6 levels, snow variables) RUC 20 20 km 50 1 h 2002 Added assimilation of GOES cloud-top data 18 RUC development – ongoing interaction with NCEP and NCAR

Obs Data for RUC Data Type ~Number Rawinsonde 80 NOAA 405 MHz profilers 31 VAD winds (WSR-88 D radars) 110 -130 Aircraft (ACARS) (V, temp) 1800 -5500 Surface/METAR (T, Td, V, p) 1500 -1700 Buoy/ship 100 -150 GOES precipitable water 1500 -3000 GOES cloud drift winds 1000 -2500 GOES cloud-top pressure/temp ~10 km res SSM/I precipitable water 1000 -4000 In testing at FSL – early 2004 GPS precipitable water ~250 Radar reflectivity / lightning 4 km Mesonet 3000 -5000 METAR cloud/vis/wx obs Freq. /12 h / 1 h / 1 h / 6 h / 1 h 19

1 Analysis ~ ‘truth’ 3 6 9 12 RUC 20 Wind forecast Accuracy -Sept-Dec 2002 Verification against rawinsonde data over RUC domain RMS vector difference (forecast vs. obs) RUC is able to use recent obs to improve forecast skill 20 down to 1 -h projection for winds

Quasi-isentropic option for non-hydrostatic model Breaking mountain wave simulation - 2 km horizontal resolution Sigma-z version Quasi-isentropic version Thick - Thin coordinate surfaces Zuwen He, 2002 Ph. D. U. Miami 21

1985 2004 Anticipated use for RUC Current users of RUC data - Aviation community air traffic mgmt - NCEP Storm Prediction Center - NWS Forecast Offices - Private forecasting - Air quality - Energy industry. . . Changes in • Number of NWP users • Frequency of access to NWP data • Ability to use shorter- and longer-duration NWP data 22 • User requrements forecast accuracy, incl. short-range

RUC changes 2004 -2007 • Assimilation of surface cloud obs/ current weather/vis, radar reflectivity, GPS … • 13 km RUC (in testing at FSL) • WRF-based “Rapid Refresh”, replacing current RUC model • More common software (model, data assimilation) for replacements to RUC, Eta, Hurricane models. • NCEP, NCAR, NOAA labs, AFWA… Beyond (IMHO) • 15 -30 min continuous update cycle • Global update cycle • Ensemble update cycles • Use of quasi-Lagrangian vertical coordinate models – ocean, atmosphere 23