NASA SST Science Team

Seattle, 8-10 November.
Chris Merchant representing SST CCI.

A real scientific buzz at this NASA SST meeting, with lots of good progress reported, particularly in understanding SST variability across the full range of time scales and space scales (literally from O(1 s, 1 cm) to O(year, global)), and thinking through how that affects our statements about SST and its uncertainty in remotely sensed products.

I (CM) presented the principal concepts underlying the approach in the SST CCI to the long-term climate data record (CDR). Generated quite a lot of questions and discussion. Generally, the idea of tying up the ATSR and AVHRR time series via radiance cross-calibration was welcomed as an innovative approach. It is different to the US route, and this is seen as helpful. AVHRR folks (Ken Casey, Bob Evans, Sasha Ignatov) seem keen to interact with us during the SST CCI, which is excellent.

I tried to communicate some of the subtleties about assessing CDR quality using the range of measures including formal independence of the information content as well as the traditional accuracy, resolution, etc. I presented the opportunities for involvement, including the algorithm selection process via the round robin. Sasha is interested in the Algorithm Selection exercise, and we discussed the contents necessary for his group to participate efficiently using their new "hybrid" algorithm.

Off-line discussions with Ken about transferring the AVHRR archive across the Atlantic have sparked some download experiments using alternative routes, but none so far have given us the data rate we need (by a factor of three or four too slow). Still need to pursue all possibilities.

Carol-Anne Clayson and Alexander Soloviev showed diurnal warming modelling results that explain the 5 pm kink in the average diurnal cycle in SST-skin: as solar insolation reduces there is a transition in the depth communicating with the atmosphere accompanied by a period of turbulent kinetic energy increasing temporarily over a greater depth. Thereafter, the thermal inertia being cooled is greater, and so the rate of cooling diminishes to the rate is sustains during the night. The diurnal cycle shape seen in their idealized (constant wind speed) model runs is essentially identical to the global average diurnal cycle shape Mark Filipiak gets from his analysis of Pierre Le Borgne's SEVIRI observations, including the peak time and the time of this TKE-related transition. They also had different explanations for the observation that the >4 K diurnal events all seem to happen in the mid-latitudes, not in the tropics. Carol-Anne finds a role for the extended length of day during mid latitude summer, while Alexander reckons they happen when the air-sea temperature difference is more positive than typically seen in the tropics. The latter idea certainly fits with the tendency of the >4 K event distribution to be nearer land masses, and could easily be tested by getting the NWP data for the events.

Some discussion from Dudley Chelton and Dick Reynolds about how sampling limits the true information in L4 analyses at higher spatial frequencies, this being relevant to the satellite-only OSTIA analysis we will generate in the SST CCI. Seems to me, the key thing is to construct proper, dynamic uncertainty estimates, including covariance effects, rather than to smooth the data, which is Dudley's recommendation. Although, for those interested in SST gradients rather than absolutes, they did show that under-sampling can introduce big problems (spurious gradients particularly from the patchiness of IR data).

Lots of enthusiasm for coming to next year's GHRSST meeting that we are hosting in Edinburgh -- should be a great event.