Ship-board radiometric measurements of the air-sea temperature difference P. J. Minnett, A. Chambers & N. Perlin Rosenstiel School of Marine and Atmospheric Science, University of Miami, USA Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Outline Conventional measurements vs radiometric measurements Marine-Atmospheric Emitted Radiance Interferometer Properties of air-sea ∆T Representation of air-sea ∆T in models, ECMWF and WRF Summary and conclusions Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Background The air-sea temperature difference (ΔT) is important in controlling the stability of the lower atmosphere and the efficiency of transfers of heat, moisture and gases from ocean to atmosphere. Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Outline Conventional measurements vs radiometric measurements Marine - Atmospheric Emitted Radiance Interferometer Properties of air-sea ∆T Representation of air-sea ∆T in models, ECMWF and WRF Summary and conclusions Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Conventional measurements Thermometers in the air and in the sub-surface ocean. – Different fluids with different thermal capacities. – Different thermometers with different calibration histories. – Air-temperature thermometer, in particular, susceptibility to solar heating. Often necessary to discard daytime measurements. Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Radiometric measurements Using an infrared spectroradiometer, can measure the skin SST and the air-temperature with a single instrument with real-time internal calibration. Skin SST measured at wavelengths where the atmosphere is relatively transparent. Air temperatures measurements made where the atmosphere is much less transparent (CO 2 emission). Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Outline Conventional measurements vs radiometric measurements Marine - Atmospheric Emitted Radiance Interferometer Properties of air-sea ∆T Representation of air-sea ∆T in models, ECMWF and WRF Summary and conclusions Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Marine-Atmospheric Emitted Radiance Interferometer Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Measured spectra of atmospheric and sea-surface emission Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014 Skin SSTNear-surface Air Temperature

Outline Conventional measurements vs radiometric measurements Marine - Atmospheric Emitted Radiance Interferometer Properties of air-sea ∆T Representation of air-sea ∆T in models, ECMWF and WRF Summary and conclusions Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Differences between conventional and radiometric air-sea ∆T Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014 Radiometric Conventional Radiometric air-sea temperature difference K Conventional air-sea temperature difference K

Long duration cruise data M-AERIs have been mounted on research ships to sample a very wide range of conditions. M-AERIs have been mounted on the Royal Caribbean Cruise Lines ship Explorer of the Seas from Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014 M-AERIs are installed where they have a clear view of the sea-surface ahead of the bow wave, and of the sky.

Histograms of air-sea ∆T Explorer of the Seas Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Histograms of air-sea ∆T Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

R/V Atlantis, 2012 Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Global distributions Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Possible feedbacks Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014 Night-time Initial disturbance warms the skin SST Initial disturbance cools the skin SST

Outline Conventional measurements vs radiometric measurements Marine - Atmospheric Emitted Radiance Interferometer Properties of air-sea ∆T Representation of air-sea ∆T in models, ECMWF and WRF Summary and conclusions Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Representation of air-sea ∆T in models Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014 M-AERI air-sea ∆T measured in equatorial Pacific from R/V Mirai ECMWF air-sea ∆T in equatorial Pacific interpolated to positions of R/V Mirai U < 3ms -1 3ms -1 < U < 5ms -1 5ms -1 < U < 9ms -1 5ms -1 < U Comparison is best for low winds. ECMWF distribution is wider, with more large – ve values. For U > 3ms -1 mean ∆T ~ x measured mean. Cases of ∆T > 0 are absent.

WRF simulations in Agulhas Current area SST provided by NOAA 0.25 o daily OI. July 2002 Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014 Air-sea ∆T follows SST perturbations Distribution shows many air-sea ∆T > 0

Measurements in Agulhas Current area Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014 Cruise area and time are different to WRF simulations, but both are in similar conditions. Histogram of measured air-sea ∆T is similar to “standard” form with very few ∆T > 0.

Outline Conventional measurements vs radiometric measurements Marine - Atmospheric Emitted Radiance Interferometer Properties of air-sea ∆T Representation of air-sea ∆T in models, ECMWF and WRF Summary and conclusions Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Summary and conclusions Infrared hyperspectral measurements from ships provide information on important aspects of air-sea ∆T. Histograms of air-sea ∆T show very similar form irrespective of region, season and SST. Form of histograms imply dominance of negative feedbacks controlling air-sea ∆T. Very few cases of ∆T > 0; limited to areas downwind of coasts, and associated with atmospheric fronts and SST fronts. Some aspects of air-sea ∆T histograms reasonably well represented in models, but as winds increase, width of modeled air-sea ∆T’s increase cf measurements (ECMWF, Equatorial W. Pacific). Air-sea ∆T’s appear to be poorly represented in models of conditions with high SST variability (WRF, Agulhas Current area). Infrared hyperspectral measurements have the potential to “recalibrate” the quantitative understanding of air-sea temperature difference and the exchanges that depend on them – implications for remote sensing of air-sea fluxes. Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014

Acknowledgements: Many students and colleagues who have facilitated or participated in the ship-board campaigns. Captains, officers and crews of many ships. Funding from NASA, NOAA, NSF. Earth Observation for Ocean-Atmosphere Interactions Science Frascati, October 2014