Foundation Sea Surface TemperatureW. Emery, S. Castro and N. Hoffman

From Wikipedia:

• Sea surface temperature (SST) is the water temperature close to the surface.

• The meaning of surface varies according to the measurement method used.

• A satellite infrared radiometer indirectly measures the temperature of a very thin layer of about 10 micrometres thick (referred to as the skin) of the ocean which leads to the phrase skin temperature (because infrared radiation is emitted from this layer).

• A microwave instrument measures sub-skin temperature at about 1 mm.

• A thermometer attached to a moored or drifting buoy in the ocean would measure the temperature at a specific depth, (e.g. at 1 meter below the sea surface) — this temperature during the day is called temperature of the warm layer.

• The measurements routinely made from ships are often from the engine water intakes and may be at various depths in the upper 20 m of the ocean.

• In fact, this temperature is often called sea surface temperature, or foundation temperature.

• Note that the depth of measurement in this case will vary with the cargo aboard the vessel.

Daytime profile

Nighttime profiles

• Most of these concepts were derived from the GODAE High Resolution SST Pilot Project (GHRSST PP)\

• Foundation SST is a fairly recent concept that acknowledges that the upper ocean is influenced by the solar insolation and wind stiring.

Can we compute SSTfnd from the available data?

• XBT profiles (research vessels and ships of opportunity, long time series)

• ARGO float profiles (global but limited vertically…below 6 m)

• CTD profiles (research vessels only, very few globally)

Red = argoBlue = XBTGreen = CTD

Daytime 2006 June

Example Profiles

Red = ARGO

Blue = XBT

• Need to examine the upper portion of these temperature profiles.

• Develop an automated technique to define the SSTfnd.

• Should sort out the erroneous temperature profiles.

• Can only have ARGO + XBT + CTD for recent years (2006 to 2009).

Some XBT Examples

Light blue = dayDark blue = night

Other examples

Light = day, dark = night

Red = ARGO, Green = CTD, Blue = XBT

SSTfnd Depth (m)

• Using the automated identification of SSTfnd we produce monthly maps of SSTfnd depth and temperature.

• Each point requires a pair of temperature profiles to be able to properly define the depth of the SSTfnd. We can mix XBT, CTD and ARGO profiles.

• Results are strongly dependent on data coverage and point out the need for more uniformly sampling the ocean to be able to identify the SSTfnd and its depth.

• Here the depths can be based on any of these data types.

SSTfnd for Jan., 2006

SSTfnd Depth (m)

SSTfnd Temperature (°C)

There is no clear relationship between SSTfnd depth and temperature.

SSTfnd April, 2006

SSTfnd Depth (m)

SSTfnd Temperature (°C)

There is again no clear relationship between SSTfnd depth and temperature.

SSTfnd July, 2006

SSTfnd Temperature (°C)

SSTfnd Depth (m)

There is again no clear relationship between SSTfnd depth and temperature.

SSTfnd Oct., 2006

SSTfnd Temperature (°C)

SSTfnd Depth (m)

There is again no clear relationship between SSTfnd depth and temperature.

SSTfnd July, 2007

SSTfnd Temperature (°C)

SSTfnd Temperature (°C)

There is again no clear relationship between SSTfnd depth and temperature.

SSTfnd July, 2007

SSTfnd Temperature (°C)

SSTfnd Depth (m)

There is again no clear relationship between SSTfnd depth and temperature.

Conclusions

• Based on the temperature profile data available it is possible to estimate SSTfnd from day-night profile pairs.

• There is no clear relationship between SSTfnd depth and temperature regardless of month, season or year.

• There are significant month-to-month, seasonal and interannual variabilities in both SSTfnd depth and temperature.

• A next step is to compare these in situ SSTfnd measurements with “coincident” satellite skin SST measurements.

• Another next step is to compare the SSTfnd depths and temperatures with coincident wind speed, solar insolation and cloud cover.