Diurnal Warming and Associated Uncertainties

November 9, 2010

Diurnal Warming and Associated Uncertainties

Gary A. Wick

NOAA ESRL/PSDNew 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.


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.


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.


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.


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 profileN

onD

im D

epth

(z)

NonDim Heat Content

Comparison throughout the day

DW

EXPERIMENTALPRODUCTS

Diurnal warming 2004-2010

Available on request from 2004

In 2011

Hourly DW available in real timeOn the zone herewith See LeBorgne et al 2010Proceedings EUMETSAT conference, Cordoba

Questions: -Hourly values every hour? Which delay -Or daily files with 24 fields?


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– 28th February to 2nd 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 ([email protected]), Gary Wick (

[email protected]) or Jacob Hoeyer ([email protected])

• On the web– http://www.ghrsst.org/Joint-DVWG,-HL-TAG-and-S

T-VAL-Workshop-2011.html

mailto:[email protected]



http://www.ghrsst.org/Joint-DVWG,-HL-TAG-and-ST-VAL-Workshop-2011.html

http://www.ghrsst.org/Joint-DVWG,-HL-TAG-and-ST-VAL-Workshop-2011.html

November 9, 2010

Intercomparison of the Uncertainty in Diurnal Warming Estimates from

Physical Mixed Layer Models

G. A. Wick1 and S. L. Castro2

with C. Merchant, A. Harris, C.A. Clayson, C. Gentemann, and Y. Kawai

1NOAA ESRL2CCAR, Univ. of Colorado


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.


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.


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/m2

• Conditions representative of tropics, mid-latitudes, and high-latitudes

• Models run for 5 days

Wick et al.


Model Simulations

Wick et al.

• Tropical conditions with u = 3 m/s, Qspeak = 800 W/m2


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


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



Sensitivity to Other Fluxes

Results shown for Modified Kantha-Clayson model

Wick et al.

Tropics Mid-latitudes


Sensitivity to Other Fluxes

Results shown for Modified Kantha-Clayson model

Wick et al.

Mid-latitudes – Tropics


Sensitivity to Solar Absorption

Modified Kantha-Clayson model, tropical conditions

Wick et al.

3-Band from Fairall 9-Band


Sensitivity to Solar Absorption

Modified Kantha-Clayson model, tropical conditions

Wick et al.

3-Band – 9-Band


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.


Real Simulations

• Example of visual comparison shown here• Models ability to reproduce observations varies

notably with conditions

Wick et al.

Skin Validation


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.



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 Resolution Interpolated 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

Diurnal Warming and Associated Uncertainties

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