GHRSST 10: Report from Diurnal Variability Working Group Report on activities of the Diurnal Variability Working Group Chris Merchant University of Edinburgh

GHRSST 10: Report from Diurnal Variability Working Group Terms of reference The diurnal variability working group of GHRSST seeks to observe, understand, model, and parameterize near-surface ocean variability on sub-daily timescales.

GHRSST 10: Report from Diurnal Variability Working Group Motivation The GHRSST drivers are: to be able to estimate real geophysical biases between different types of ‘sea surface temperature’ (SST) observations to permit high temporal resolution SST analyses to maximise data use in operational systems to combine different observations properly in operations and re-analysis.

GHRSST 10: Report from Diurnal Variability Working Group Mean ocean diurnal-warming cycles SEVIRI/NWP based model, local time 0 K 1 K 2 K

GHRSST 10: Report from Diurnal Variability Working Group Peaky and streaky

GHRSST 10: Report from Diurnal Variability Working Group Peakiness and streakiness: Time history of wind minimum & insolation 10 am 1 m s -1 contour 2 pm 1 m s -1 contour Instantaneous model: >1.5 K Persistence model: >5 K

GHRSST 10: Report from Diurnal Variability Working Group “DVWG challenge” Diurnal Variability Analysis: Spatially complete blend of diurnal warming estimated from temporal evolution of observed SST from model-based knowledge appropriately combined to give estimated subdaily time evolution of skin/subskin/buoy-depth SST

GHRSST 10: Report from Diurnal Variability Working Group Diurnal Variability Working Group Fifth working group meeting in Rome

GHRSST 10: Report from Diurnal Variability Working Group Working Group programme Session 1 -- DSST MODELS –Gary Wick: study of efficiency of look-up table models based on K-C turbulence modelling –Mark Filipiak: full dynamic range empirical model of DSST driven by NWP –Yoshimi Kawai: experience with Godfrey- Schiller model Session 2 – OBSERVATIONS –Helen Beggs: Tropical Warm Pool intensive observation experiment -- plans

GHRSST 10: Report from Diurnal Variability Working Group Working Group programme Session 2 contd. –Chris Merchant: Multi-sensor observations of large diurnal warming events –Yoshimi Kawai: Report of modified ARGO profilers for near surface –Salvatore Marullo: Combining DSST observations in the Atlantic –Steinar Eastwood: High-latitude warm spots

GHRSST 10: Report from Diurnal Variability Working Group Working Group programme Session 3: DVA and miscellaneous –Pierre Le Borgne: Data driven DSST analysis –Helen Beggs: Skin SST analysis at BoM –Chris Merchant: The GlobColour depth of heated layer product –Carol-Anne Clayson: Seaflux interest in DV –Sandra Castro: length scales and self- similarity of DSST features

GHRSST 10: Report from Diurnal Variability Working Group

To what extent might these observations support understanding of skin-foundation differences? Steve Riser in DVWG break out session, Tues.

GHRSST 10: Report from Diurnal Variability Working Group METOP MODIS AQUA NIGHT BEFORE Around 11 a.m. 68 o N 5 o E, 2 June km

GHRSST 10: Report from Diurnal Variability Working Group Experimental DVAs Data driven (SST differences, day-night) Analyses differences (skin-foundation) Blending of NWP-driven model and data ECMWF NWP wind, SSI Nudge NWP Observed DSST ECMWF maximum wind & integrated Q fields DSST-based Wmax and Qint DSST analysis Invertible DSST model

GHRSST 10: Report from Diurnal Variability Working Group Based on SEVIRI SSTs + data driven analysis Cloudy areas set to zero diurnal warming 1 May 2006

GHRSST 10: Report from Diurnal Variability Working Group Estimates of DSST field before and after observation time

GHRSST 10: Report from Diurnal Variability Working Group Interaction with Data Buoy Cooperation Panel In conjunction with SSES/Val TAG and following the Science Team letter, we converged on the following recommendations to the DBCP (1) That comprehensive hourly reporting from drifting buoys as standard will be of immediate benefit to fundamental knowledge of diurnal variability globally noting that such reporting is very likely to be heavily utilized within GHRSST diurnal variability and validation activities immediately and in the future by operational DVAC. (2) Reporting in metadata of the nominal or design depth in calm water of the drifting buoy SST to an absolute accuracy of ±5 cm is encouraged to facilitate diurnal variability analysis. (3) Reporting of geographical location with an absolute accuracy of ±0.5 km or better is important for high resolution SST analysis and satellite SST validation. (We note that calculation of hourly velocity vectors arose in the discussions, and would require ±0.01 km resolution.) (4) Absolute accuracy of drifting buoy SST of ±0.05 K is recommended based on the needs of satellite SST validation, with SSTs reported with a resolution of 0.01 K (to fully resolve diurnal cycles in SST). (5) That the netCDF CF-1.3 standard name table is adopted for use by reporting agencies. (6) Reporting of the time of SST measurement to an absolute accuracy of ±5 minutes. (7) Reporting at hourly intervals (for purposes of matching to satellite observation and resolving diurnal cycles in time), but there is no requirement that the reports be made on or close to integer UTC hours.

GHRSST 10: Report from Diurnal Variability Working Group New ongoing projects Diurnal Variability Field Inter-comparison –Comparisons of various estimates of the diurnal cycle for defined periods and locations (Atlantic, Global) Intensive Observation Projects –ALADIN+ –Tropical Warm Pool+ –WASPARC Diurnal Variability Analysis Any new participants?