November 9, 2010 Diurnal Warming and Associated Uncertainties Gary A. Wick NOAA ESRL/PSD New Chair, GHRSST DVWG

SST Science Team MeetingNovember 9, 2010 Outline The diurnal warming problem Recent results and research directions Specific results related to uncertainties in physical modeling of diurnal warming Wick et al.

SST Science Team MeetingNovember 9, 2010 What is the Problem? SST varies with time and depth Need to account for DW to: –Reference an SST value to another time Combination of observations from different times of the day –Reference values to a different depth Construction of foundation analyses Regression against observations at depth Wick et al.

SST Science Team MeetingNovember 9, 2010 Why the Difficulty? Warming is a complicated function of multiple parameters –Models still uncertain –Not all parameters easily measured from space Need complete time history of forcing parameters –Sampling of available parameters is not continuous –All parameters subject to measurement uncertainties Observations/validation still insufficient Wick et al.

SST Science Team MeetingNovember 9, 2010 A Fundamental Question Can we estimate diurnal warming with enough skill to improve SST products? To what degree is added complexity desired or justified? –Physical models vs. empirical parameterizations At what point is the data insufficient? Requires a detailed understanding of uncertainties Wick et al.

SST Science Team MeetingNovember 9, 2010 Progress to Date Work within the GHRSST DVWG and independent research has led to: Improved models Improved understanding and characterization of DW events Improved resources for evaluation of models –Aladin –Tropical Warm Pool+ Initial diurnal warming analyses Wick et al.

POSH Profiles of Surface Heating (POSH) –F96 –Absorption –Reduce accumulated heat/momentum –Structured profiles of temperature within the warm layer (CG empirical or Kantha/Clayson (WICK) profiles)

Dimensionless DW profile NonDim Depth (z) NonDim Heat Content

Comparison throughout the day

DW EXPERIMENTAL PRODUCTS Diurnal warming Available on request from 2004

In 2011 Hourly DW available in real time On the zone herewith See LeBorgne et al 2010 Proceedings EUMETSAT conference, Cordoba Questions: -Hourly values every hour? Which delay -Or daily files with 24 fields?

SST Science Team MeetingNovember 9, 2010 DVWG Priorities Provision of diurnal warming analyses Guidance on recommended/consensus approaches Improved estimates of uncertainties in diurnal warming products Wick et al.

Joint DVWG, HL-TAG, ST-VAL Workshop When – 28 th February to 2 nd March 2011 Where – University of Colorado, Boulder, USA Why – To allow more time to address the key scientific issues – To recognise the high degree of commonality between each group

Outline format Three main topics – High latitude SST estimation Retrieval, cloud masking, sea-ice analyses, both Arctic and Antarctic regions – Diurnal variability observation & analyses Arctic, SEVIRI, POSH, shallow water, TWP+ – SST uncertainty characterisation & SSES Uncertainty budgets, next generation radiometers, Argo, SSES Main plenary talks (20 min), with open discussion (5 min highlight talks) and working breakout sessions Open mainly to DVWG, HL-TAG and ST-VAL groups – 16 people confirmed with another 14 likely to attend – Some oral slots not yet taken

For more information Contact – Gary Corlett Gary Wick or Jacob Hoeyer On the web – ST-VAL-Workshop-2011.html ST-VAL-Workshop-2011.html

November 9, 2010 Intercomparison of the Uncertainty in Diurnal Warming Estimates from Physical Mixed Layer Models G. A. Wick 1 and S. L. Castro 2 with C. Merchant, A. Harris, C.A. Clayson, C. Gentemann, and Y. Kawai 1 NOAA ESRL 2 CCAR, Univ. of Colorado

SST Science Team MeetingNovember 9, 2010 Context GHRSST Diurnal Variability Working Group –Providing recommended approaches to estimating the amount of diurnal warming present in satellite observations –Sub-effort to compare the ability of existing models to reproduce observations of diurnal warming Constructing the SST Error Budget –What is the contribution of diurnal warming to the uncertainty of satellite SST products –Primarily relevant to SST analyses Wick et al.

SST Science Team MeetingNovember 9, 2010 Approach Diurnal warming models tested for both idealized and real forcing Models initially considered –COARE warm layer model –Modified Kantha-Clayson –POSH –Generalized Ocean Turbulence Model (GOTM) – k-epsilon approach Tested models with common solar penetration model Used common skin layer treatment Used common vertical grid Fluxes computed with COARE model and used in other models Wick et al.

SST Science Team MeetingNovember 9, 2010 Approach Diurnal warming models tested for both idealized and real forcing Models initially considered –COARE warm layer model –Modified Kantha-Clayson –POSH –Generalized Ocean Turbulence Model (GOTM) – k-epsilon approach Tested models with common solar penetration model Used common skin layer treatment Used common vertical grid Fluxes computed with COARE model and used in other models Wick et al.

SST Science Team MeetingNovember 9, 2010 Idealized Forcing Goal to compare behavior at low wind speeds and assess sensitivity to factors including solar penetration model and environmental conditions Constant wind speed from 0.5 – 10 m/s Peak insolation from 50 – 1000 W/m 2 Conditions representative of tropics, mid- latitudes, and high-latitudes Models run for 5 days Wick et al.

SST Science Team MeetingNovember 9, 2010 Model Simulations Wick et al. Tropical conditions with u = 3 m/s, Qs peak = 800 W/m 2

SST Science Team MeetingNovember 9, 2010 Modeled Warming at the Skin Tropical conditions Results shown at 13:30 on day 3 of simulation Warming computed relative to 25-m depth Wick et al. Modified Kantha-Clayson COARE

SST Science Team MeetingNovember 9, 2010 Modeled Warming at 1-m Depth Wick et al. Tropical conditions Results shown at 13:30 on day 3 of simulation Warming computed relative to 25-m depth Modified Kantha-Clayson COARE

SST Science Team MeetingNovember 9, 2010 Sensitivity to Other Fluxes Results shown for Modified Kantha-Clayson model Wick et al. TropicsMid-latitudes

SST Science Team MeetingNovember 9, 2010 Sensitivity to Other Fluxes Results shown for Modified Kantha-Clayson model Wick et al. Mid-latitudes – Tropics

SST Science Team MeetingNovember 9, 2010 Sensitivity to Solar Absorption Modified Kantha-Clayson model, tropical conditions Wick et al. 3-Band from Fairall9-Band

SST Science Team MeetingNovember 9, 2010 Sensitivity to Solar Absorption Modified Kantha-Clayson model, tropical conditions Wick et al. 3-Band – 9-Band

SST Science Team MeetingNovember 9, 2010 Real Forcing Goal to evaluate absolute accuracy relative to observed warming and sensitivity to temporal resolution of forcing parameters ETL cruise database from the R/V Ronald H. Brown –Validation against sea-snake near-surface temperature –Data courtesy C. Fairall R/V Ronald H. Brown cruises with the CIRIMS –Validation against skin temperature observations from the CIRIMS –CIRIMS data courtesy A. Jessup Models forced with continuous meteorological observations from the ship Wick et al.

SST Science Team MeetingNovember 9, 2010 Real Simulations Example of visual comparison shown here Models ability to reproduce observations varies notably with conditions Wick et al. Skin Validation

SST Science Team MeetingNovember 9, 2010 Absolute Accuracy Models run for entire set of cruises and differences relative to observations binned as a function of local solar time Results shown for wind speeds less than 4 m/s Mean bias can be reduced to small levels but RMS differences of O(1K) remain even with full forcing data Wick et al. Modified Kantha-ClaysonCOARE

SST Science Team MeetingNovember 9, 2010 Impact of Forcing Resolution Simulations re-run for Modified Kantha-Clayson model and forcing data sampled at 6-hour intervals Significant degradation observed in both bias and RMS relative to observations Wick et al. Full ResolutionInterpolated 6-Hourly Data

SST Science Team MeetingNovember 9, 2010Wick et al. Conclusions Modeled diurnal warming highly variable at lowest wind speeds Significant sensitivity to solar penetration model Warming also exhibits some sensitivity to background fluxes Bias in warming predictions can be largely removed with tuned models RMS uncertainty in predicted warming on O(1K) at low wind speeds