PIPS Development/Validation and a path to automated ice charts Michael Van Woert U.S. National Ice Center IICWG-IV, St. Petersburg 7 April 2003

PIPS History PIPS 1.0 (1980’s) -- Regional Hibler ice model Climatological ocean (currents and heat fluxes). Separate models for the Barents and Greenland Seas (25 km). PIPS 2.0 (1996) Northern hemisphere Coupled Hibler ice model/Cox ocean model 0.28 degree grid resolution (17-34 km) 15 vertical levels Solid wall boundaries Ocean loosely constrained to Levitus climatology Initialized with NIC/SSMI analysis.

Cox Ocean Model Hibler Ice Model Polar Ice Prediction System 2.0 Forecast Restart (ice-ocean) or Climatology and SSMI Ice Concentration Atmospheric Forcing NOGAPS Cox Ocean Model Hibler Ice Model Model Output Ice Drift Ice Thickness Ice Concentration Ocean Currents Ocean Temps Ocean Salinity 24-hour Forecast for Ice-Ocean Restart

PIPS Data Initialization Model initialized daily from SSM/I ice concentration (CAL/VAL algorithm) PIPS ice concentration is replaced only at locations where observed ice concentration is >80% or <50% and the difference between the two fields is >10% or >5% respectively PIPS ice thickness and ocean mixed layer temperature fields are adjusted to be consistent with the SSM/I observations CAL/VAL 2/26/02 PIPS Analysis 2/26/02 12/7/2018 IAHR

PIPS 2.0 Atmospheric Forcing Model uses daily NOGAPS fields (1 degree resolution) Fields used: Surface Pressure, Surface Air Temperature, Surface Vapor Pressure, Net Shortwave Radiation and Downwelling Longwave Radiation, surface wind stress

Operational Oceanography The norm for ocean forecast verification… “It looks like the ocean, it must be correct.”

For Dec 30, 2000 a) IABP buoy drift and pressure b) PIPS ice drift c) PIPS ice concentration d) PIPS ice thickness

Forecast Skill Scores #1 Af = error of the forecast system Ap = error of a perfect forecast Ar = error of a reference forecast In this formulation SS represents the improvement in accuracy of the forecast with respect to the reference forecast, relative to the total improvement in accuracy.

Forecast Skill Scores #2 Error defined as: Skill score becomes f = Forecast field O = Observed or analyzed field R = Reference field (Yet to be defined) P = Perfect forecast field (Forecast = Observed) Note: MSE for a perfect forecast is 0. That is: MSE(P,O) = 0.

Forecast Skill Scores #3 Perfect forecast SS=1; MSE(f,O)=0 No forecast skill SS=0; MSE(f,O)=MSE(R,O) In general: SS>0 (skillful) when MSE(f,O) < MSE(R,O) SS<0 (unskillful) when MSE(f,O) > MSE(R,O) MSE(R,O) is the yardstick for measuring skill!

Climatological Skill Scores 5% Threshold SS24 (Solid line) ~ 0.8 PIPS Does much better than a climatological forecast

Persistence Skill Scores 5% Threshold SS24 (solid line) ~ 0.1 to 0.3 PIPS slightly better than a persistence forecast in most months

CLIPER Skill Scores 5% Threshold SS24 (solid line) ~ -0.2 to 0.2 Linear combination of CLImatology and PERsistence does better than PIPS during the months of Oct-Feb! PIPS only slightly better than CLI-PER during other months Forecast model must be exceptional to add significant skill!

PIPS 3.0 - Goal New ice model based on technology gained in the 1990’s. Include the ability to forecast regions of lead formation (anisotropic rheology) Coupled to an updated ocean model Using improved atmospheric forcing Improved data assimilation 10 km grid resolution

Global Ocean Model (NCOM) CICE Model Polar Ice Prediction System 3.0 Forecast Restart (ice-ocean) or Ocean Analysis/ SSMI Ice Concentration and Satellite Ice Drift Atmospheric Forcing NOGAPS Global Ocean Model (NCOM) CICE Model Model Output Ice Drift Ice Thickness Ice Concentration Ice conv/div Ice strength Ocean Currents Ocean Temps Ocean Salinity 24-hour Forecast for Ice-Ocean Restart

PIPS 3.0 – Global Ocean Model PIPS 3.0 will be coupled to the NCOM global ocean model (includes daily data assimilation) 1/8 degree resolution with polar cap Arctic resolution ~10 km Model run time (with analysis) – 12 min/day using 128 processors (IBM Winterhawk 2)----5 days = 60 hours, 8 days = 96 hours

NCOM Global Grid Northern Hemisphere Use lat-long grid below 32 N (grid extends to 78.5 S). Use curvilinear grid above 32 N to cover the arctic. Use dx=dy locally from about 50 S to 32 N. Grids tried: 1/2 deg (dx = 55.6 km at eq) from 72 S to 72 N (720 x 422 x 30). 2/3 deg (dx = 78.2 km at eq) global (512 x 320 x 30). 1/3 deg (dx = 39.1 km at eq) global (1024 x 640 x 20). ~1/4 deg avg. 1/6 deg (dx = 19.6 km at eq) global (2048 x 1280 x 40). ~ 1/8 deg avg. AMOP 9; 1/8/01

Global NCOM Ocean Model www7320.nrlssc.navy.mil/global_ncom 41 vertical sigma-z levels NOGAPS winds with the assimilation 1m z-level top, 20 sigma of MODAS synthetic T/S fields 48-hr forecast each day Polar Overlap

PIPS 3.0 Ice Model LANL model CICE –Hunke, Lipscomb, Dukowicz) CICE, developed at Los Alamos National Laboratory( LANL), is available for public use via their website.

CICE – LANL Sea Ice Model EVP (efficient, improved response to forcing) Energy conserving Bitz and Lipscomb (1999) thermodynamics Multi-category, linearly remapped ice thickness Energy-based ice ridging Other improvements to physics parameterizations

PIPS 3.0 – Atmospheric Forcing PIPS 3.0 will be driven by the Navy’s global atmospheric model (NOGAPS) NOGAPS commenced running at 50 km resolution on Sept 25, 2002

Planned Data Initialization /Assimilation SSMI will be upgraded to the NASA Team 2 alogrithm Assimilation of satellite derived ice drift and buoy drift data (Preller et al., Tos, 2002) if available. Assimilation of ocean observations into the coupled ice ocean models can improve the sea ice forecast by improving the ocean model forecast

PIPS 3.0 March Ice Concentration

CICE results from 1-year simulation using 1984 ECMWF forcing

Model Initialization/Nowcast Goal: To develop an fully automated sea ice chart (nowcast). Minimum requirements: C, h, V Current practices: PIPS ice concentration (C)is updated at locations where observed ice concentration is >80% or <50% and the difference between the two fields is >10% or >5% respectively PIPS ice thickness (h) and is adjusted to be consistent with the SSM/I PIPS ice motion (V) is being update with Objective Interpolation Issues: Concentration and thickness sensitive to large SSM/I errors Concentration observations not necessarily consistent with ice dynamics

Initialization Methods Simple Replace model with observations or employ basic weighting (Method for PIPS Sea Ice Conc. Initialization) Statistical Minimize errors in statistical (e.g. least squares) manner Optimal Interpolation (PIPS 3.0, Ice Drift Assimilation) Kalman Filter Variational Minimize cost function (e.g. disagreement between model and observations) subject to constraints (e.g., model physics) Complex and can be difficult to develop

The Model Velocity: Concentration: Thickness: Sh is the total ice growth Sc is the rate at which ice-covered area is created by melting and freezing

Free Drift Model Free Drift 2% of Wind speed 20o Right of wind

Variational Method Data inputs: Prior day’s, 24 hour forecasts of u24, v24, C24, h24 Current days 85 GHz drift (uo, vo) Current day’s SSM/I ice concentrations Co Impose constraints fh(u,v,h)=0 fC(u,v,C)=0 The sprit of the approach is to keep the initialized fields close to the observations while exactly satisfying the constraints. l1 and l2 are unknown constant Lagrange Multipliers the w’s are data-specific, user-defined weights

Conclusions T=PIPS 2.0 -- 24 hour Skill referenced to climo ~ 0.85 Due to daily reinitialization, PIPS provides good forecast relative to climo T= PIPS 2.0 -- 24 hour Skill referenced to persist ~ 0.2 (Mar-Oct) Sea ice fields most variable in the MIZ Poor performance during “freeze-up” – MIZ parameterizations & forcing ? T=24 hour PIPS Skill referenced to CLIPER ~ 0.1 (Mar-Oct) Non-skillful forecasts Oct – Feb During winter months linear combination of persistence & climo does best PIPS 3.0 will come online shortly Will include assimilation of sea ice motion Further work is required to accurately initialize PIPS Ancillary benefit will be an Automated Sea Ice Chart

The End