Impact of Microwave SST Dr. Craig Donlon and The International GHRSST Science-Team

Group for High Resolution Sea Surface Temperature SST requirements for GHRSST GODAE defined the minimum data specification required for use in operational ocean models: –global coverage (all weather implies microwave SST) –a spatial resolution of 10 km or better –an accuracy of 0.5ºC or better –updated every six hours & be available in near real time. GCOS defines the requirements for SST ECV –Bias <0.1 K for all global oceans, –Stability 0.05 K decade -1 (e.g. Merchant et al for the AATSR CDR) GHRSST data products should properly address the difficult issues of: –sea ice edge (implies high resolution microwave data) –diurnal variability –include uncertainty estimates to facilitate their use by data assimilation systems.

Group for High Resolution Sea Surface Temperature Measuring the ocean SST MEDS GTS Drifter data, May 2003 YSI Thermistors Practically zero in situ coverage! Available every day from

Group for High Resolution Sea Surface Temperature Polar Orbiting infrared has high accuracy & spatial resolution Geostationary infrared has high temporal resolution Microwave Polar orbiting has all-weather capability GHRSST Builds on EO complementarities Data Merging In situ data provide reality in all weather conditions

Group for High Resolution Sea Surface Temperature Microwave emission low frequency, ~ 1.4 GHz gives access to ocean salinity. ~ 6-7 GHz offer the best sensitivity to sea surface temperature, but contains error contributions due to salinity and wind speed can be partly removed using measurements around GHz. NWP data required (or scat winds) Measures SSTsub-skin ~1mm depth After Wilheit et al Salinity SST Wind speed

Group for High Resolution Sea Surface Temperature RFI Errors (hot lobe) in AMSRE SST due to refection of TV broadcasts in Europe at certain view angles (C. Gentemann, RSS)

Group for High Resolution Sea Surface Temperature Seasonal bias in IR and PM SST coverage October 1999 to September 2000 (L. Guan, ORSI, China) SST Availability in region I Only PM SST’s (TRMM TMI) provide unbiased sampling throughout the year Study Region

Group for High Resolution Sea Surface Temperature Temperature ( o C) Arabian Sea WHOI Mooring Data - Spring 1995 (From the work of A. Stuart-Menteth) (1mm data estimated using Fairall et al. (1996)) Year Day SSTfnd (Foundation Temperature) Temperatures at all depths collapse to the same value before local sunrise Impact of diurnal SST variability

Group for High Resolution Sea Surface Temperature CF1.3 standard names for SST Depth (z) 10  m 1 mm 1 m 10 m SST skin – SST 10m (K) 1. Night-time (or strong winds) profile in red 2. Day time situation, strong solar radiation and light winds shown in black CF1.3: sea_surface_skin_temperature GHRSST: SSTskin CF1.3: sea_surface_subskin_temperature GHRSST: SSTsubskin CF1.3: sea_water_temperature GHRSST: SSTdepth CF1.3: sea_surface_foundation_temperature GHRSST: SSTfnd CF1.3: sea_surface_temperature GHRSST: SSTint sea_surface_skin_temperature (SSTskin) sea_surface_subskin_temperature (SSTsubskin) sea_water_temperature at depth z (SST depth SST 1m ) sea_surface_foundation_temperature (SSTfnd) Night-time (or strong winds) profile in red sea_surface_temperature (SSTint)

Group for High Resolution Sea Surface Temperature Conclusion 1 and 2 1.The GHRSST- requirements cannot be met without access to passive microwave SST data preferably at a resolution of 10km or better. 2.SST measurements must be qualified using standard names.

Group for High Resolution Sea Surface Temperature Hurricane research August 25, 1998 Bonnie caused significant cold upwelling not evident in AVHRR SST because of the clouds surrounding the storm. When Danielle passed over the cold wake of Bonnie the intensity decreased sharply and the storm veered to the NE. (C Gentemann, Remote Sensing Systems)

Group for High Resolution Sea Surface Temperature Hurricane Dean cold upwelling 21st August 2007 Use of GHRSST satellite data (esp. microwave) allows changes in SST to be rapidly detected. Old NWP SST OSTIA SST minus Climatology : Contours at 0.5° intervals.

Group for High Resolution Sea Surface Temperature Tropical Cyclone prediction Time series of Hurricane Katrina every 6 hours (12 UCT 27 August to 0600 UTC 30 August 2005, from the best track data (black), the IR-only SST analysis run (blue) and the IR+MW SST run (red). A) The sea level pressure. (SLP) B) The track forecast errors. Image from J. Cummings US Navy GHRSST SSTs give improved TC forecast track errors

Group for High Resolution Sea Surface Temperature Impact of high-resolution SST on ECMWF wind stress (D Chelton, Oregon State ) ECMWF increased the resolution of the operational model grid to T511 (~0.35°) in 2001 Also changed from Reynolds weekly SST analysis to NOAA RTG-SST - higher resolution (0.5°) analysis (2001/5/9) The response of the ECMWF wind stress field to SST is only about half as strong as the coupling inferred from QuikSCATwinds and TMI SST Higher resolution SST has a positive impact on operational surface wind field - High resolution SST is important for NWP From Chelton 2005

Group for High Resolution Sea Surface Temperature Impact of high-resolution SST boundary specification on NWP - Meso Eta forecast, 30 th December 2000 Dec 2000: NWS Meso Eta model provided poor guidance –failing NOAA-14 AVHRR – swap out to Reynolds SST analysis –forecast deeper cyclogenisis and stronger frontal activity & precip (>15cm) than other models along the Atlantic coast. Following a full review, the poor forecast was attributed to the lack of structure and incorrect gradients in the analysis SST (Eta used 1° Reynolds in this case). A high resolution (0.5°) variable covariance SST analysis (now called the RTG_SST) was developed and tested during the investigation High resolution SST provided the best bottom boundary condition (sharper gradients) along the E. Coast of the USA and had the most influence on this storm development. This conclusion was significant highlighting the impact of a poor SST boundary condition. See NOAA NWS Tech. Proc. Bull. 477 Recent evidence using HadGEM1a on the Earth Simulator finds a similar result. (From Thiébaux et al, 2003)

Group for High Resolution Sea Surface Temperature Operational SST & Sea Ice Analysis Daily 1/20° (~5.6km) global SST analysis. –Analysis of the ‘foundation’ SST [pre- dawn or below the diurnal warm layer]. Blend of data sources, using satellite (microwave & IR) and in situ data. –Using many GHRSST data products. –Almost all Medspiration products. Now running daily, operationally. Using a variational scheme, with persistence based background. Uses sea ice analysis performed by EUMETSAT OSI-SAF (met.no / DMI). Sample analysis for 19 Apr 2007

Group for High Resolution Sea Surface Temperature OSTIA : Source Data Sensor (Platform) TypeResolutionData SourceCoverageSub sa- mpling AMSR-E (Aqua) Microwave~25km (swath) Remote Sensing Systems (ssmi.com). L2P Format. Global (~1 million/day) 2222 TMI (TRMM)Microwave~25km (swath) Remote Sensing Systems (ssmi.com). L2P Format. Tropics (~0.5 million/day) None AATSR (EnviSAT)Infra-red~1km (swath)Medspiration RDAC, L2P Format Global (~2 million/day) 3333 AVHRR -LAC (NOAA 17 & 18) Infra-red~1/10° (Grid) Medspiration RDAC, L2P Format (NAR) & NAVOCEANO-JPL North Atlantic (grid) (~0.5 million/day) 3333 AVHRR -GAC (NOAA 18) Infra-red~1km (Swath) NAVOCEANO-JPLGlobal (~2 million/day) None AVHRR-FRAC (METOP-A) Infra-red ~1km (Swath)Ifremer / CMSGlobal (~2 million) 8989 SEVIRI (MSG1)Infra-red0.1° (Gridded)Medspiration RDAC, L2P Format Atlantic sector (~2 million/day) None In-SituShips, drifting and moored buoys. In-situMet Office MetDB (GTS) Global (~25,000 /day) None Sea IceSSMI, Gridded10km, Gridded.OSI-SAF (Met.no)Global.None.

Group for High Resolution Sea Surface Temperature Warm Arctic 2007 Exceptionally warm Arctic SSTs due to sea ice retreat & clear sky conditions. (from NSIDC)

Group for High Resolution Sea Surface Temperature Old NWP SST didn’t capture the warming (no Microwave data). OSTIA - climatology OSTIA – NWP SST NWP Bias 925hPa, 48hr forecasts

Group for High Resolution Sea Surface Temperature August NWP Trial Results… OSTIA SSTs substantially reduced the negative bias seen with NWP SSTs at 850hPa. NWP SSTs OSTIA SSTs Forecast Range ( to 5 days) Mean Error (K)

Group for High Resolution Sea Surface Temperature OSTIA improved the RMS and bias in the NWP forecasts during the trial period. RMS Error Mean Error Reduced Bias at low levels Pressure Level

Group for High Resolution Sea Surface Temperature OSTIA gets accelerated. Problems with the Arctic SSTs lead to strong drive from NWP to improve the SST –SST’s wrong in the Arctic –Atmospheric sounder boundary conditions were wrong –Negative impact on forecasts Operational implementation was accelerated –Trial for August 07 showed improvements in surface temperature (but slightly exaggerated an existing warm bias at 500hPa). –Net impact was positive (good). Resulted in an ‘accelerated’ implementation in the Met Office regional and global NWP models (by October 2007) Impact largely due to Passive Microwave SST’s

Group for High Resolution Sea Surface Temperature GHRSST / OSTIA at ECMWF OSTIA / GHRSST – OPER / NCEP August 2008 Validation against buoy data (North of 70 N, August 2008) OPER / NCEPGHRSST / OSTIA OPER / NCEP SST RTG SST RTG SST 0.5 x 0.5 degrees 0.5 x 0.5 degrees

Group for High Resolution Sea Surface Temperature Conclusion 3 3.Passive Microwave SST improves operational NWP at global and regional scales.

Group for High Resolution Sea Surface Temperature Summary Passive microwave SST’s are essential to meet the requirements of GHRSST, NWP and Ocean forecasting systems. Passive microwave SST’s are essential for the climate data record as they avoid the ‘clear sky’ bias associated with persistent cloudy areas.