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Presentation given at the 21st. GHRSST Science Meeting (XXI), June 1-4, 2020

Poster presentedat the 20thGHRSST science meeting (XX), Frascati, Italy, June 3- 7, 2019.

Presentation given at the 20thGHRSST science meeting (XX), ESA/ESRIN, Frascati, Italy, June 3- 7, 2019.

During daytime, under low winds and due to solar heating, the skin and sub-skin temperatures, typically measured by satellites can increase by several degrees compared to the foundation temperature. Diurnal variability has been observed in the Mediterranean [5], western North Atlantic [1] and the global ocean [2,3] from in situ and satellite observations. Diurnal heating has been reported at higher latitudes [4] and an extended study to characterise the regional patterns of diurnal SST variability over the Atlantic Ocean and the European Seas [5], showed frequent occurrences of diurnal warming events reaching several degrees, in the Baltic Sea.Nonetheless, diurnal SST variability it is not fully resolved by ocean and coupled oceanatmosphere models. Although some of the important diurnal variability and cool skin effects [6] have been shown to be reproducible [7], the vertical grid resolution of the models is of meter-scale. In addition, regional CMEMS ocean forecasting systems only assimilate a single SST field per day, representative of night-time conditions when the water column is well mixed and thus, no diurnal signal is present. Such simplification of the SST has been reported to cause biases in the estimated surface fluxes [8,9]. The implications associated with the lack of a properly resolved SST daily cycle in atmospheric, oceanic and climate models have been quantified in terms of heat budget errors mostly in the Tropics. Heat flux errors associated with the warm layer development were reported in [9] to range between 10 and 50 Wm-2. In regions with diurnal warm layer formation, [10] reported an annual mean surface flux out of the ocean that reached up to 9 Wm-2. In addition, strong SST diurnal signals can complicate the assimilation of SST fields in ocean and atmospheric models, the derivation of atmospheric correction algorithms for satellite radiometers and the merging of satellite SST from different sensors [11]. Not accounting for the daily SST variability can cause biases in the prediction and modelling of algal blooms, especially as cyanobacteria blooms in the Baltic Sea are promoted by high SST values [12] - and the estimated net flux of CO2, as the outflux of oceanic CO2 is positively correlated with the increase of SST [13].Various models exist for the description of the diurnal cycle and their complexity varies from empirical parameterisations, based on various input parameters such as the surface winds and heat fluxes, to turbulent closure models. Parameterisation models are typically developed based on observational evidence at specific locations and depths, thus carry the uncertainty of their parameters and forcing fields, typically from Numerical Weather Prediction (NWP) models not resolving the SST diurnal cycle. Such parameterisations were compared to SEVIRI SST derived signals in the North Sea and the Baltic Sea [14] with moderate results. More sophisticated models such as turbulence closure models can resolve the vertical extend of the diurnal signal but are computationally expensive. The one-dimensional General Ocean Turbulence Model [15] was shown in [16] to perform very well in reproducing the vertical temperature structure as described by satellite SST and buoy measurements. The success of such modelling attempts highly depends on the accuracy of the input fields, typically obtained from atmospheric models. Consequently, there is a need to evaluate the impact of properly resolving the daily variability of SST in atmospheric models as well. When examining very strong diurnal warming cases, it was found that updating the SST every 6hours in the meso-scale model WRF, as opposed to using one daily value, resulted in average day-time differences of up to 20% for the 10 m winds and up to 40% for the surface heat flux [17].The “Improved Diurnal Variability Forecast of Ocean Surface Temperature through Community Model development (DIVOST-COM)” project will “improve the representation of diurnal variability and cool skin layer in forced ocean and coupled ocean-atmosphere models” and the aim of this report is to provide an overview of the project. Section 2 describes the project methodology, section 3 describes the background and expected outcomes while the main conclusions are presented in Section 4.

Presentation given at the 18th GHRSST science meeting (XVIII), Qingdao, China, June 5 -9, 2017

Presentation given at the 14th GHRSST science meeting (XIV), Woods Hole, MA, USA, June 17- 21, 2013.

Presentation given at the 14th GHRSST science meeting (XIV), Woods Hole, MA, USA, June 17- 21, 2013.

This study presents some preliminary results of the ESA Support To Science Element (STSE) funded project on the Diurnal Variability of the Sea Surface Temperature, regarding its Regional Extend and Implications in Atmospheric Modelling (SSTDV:R.EX.–IM.A.M.). Comparisons of SEVIRI SST with AATSR show zero biases and standard deviations around 0.5 K mostly in the Tropics where SEVIRI is found colder. Sensitivity tests on the methodology to derive foundation temperature fields show that using only quality 5 SEVIRI data results in warmer foundation fields while there is an added 0.2 K variability when using multi-day composites. Diurnal warming signals exceeding 2 K are identified in the European Seas but also in the mid-latitudes of the North and South Atlantic as well as in areas with strong currents. In the attempt to connect temperature measurements from satellites and in situ instruments, the 1-dimensional General Ocean Turbulence Model (GOTM) is applied. Preliminary results show that the initial temperature and salinity profiles may give a warmer start-up in the model while the light extinction scheme is a controlling factor for the amplitude and vertical extend of the daily signal.

Satellite Eye for Galathea 3 is a project funded by Egmont Fonden and the participating institutes – Risø DTU, DTU Space, ESA Eduspace, Niels Bohr Institute at University of Copenhagen, GRAS and DMI - in the period 2006 to 2008. During the Galathea 3 expedition around 10.000 satellite images were collected along the entire route. The expedition took place from 11th August 2006 to 25th April 2007. The satellite images were shown in near-real-time on Google Earth along with near-real-time ship observations. Based on the satellite images, the ship observations and through collaboration with many Galathea 3 research projects educational material for upper secondary schools were being prepared. A total of 41 educational projects were being developed. Most of this information was published at EMU, the Danish portal for schools during 2007 in Danish and English. In addition, a satellite image with a short text was published each week at the homepage www.satelliteeye.dk . During 2007 the Satellite Eye team jointly with Nature & science prepared an educational film ‘Satellite Eye – Galathea 3 fra rummet’. This work is funded by The Danish Ministry of Education, Tips- og Lottopuljen. The film will be sent to upper secondary schools along with the Satellite Living Atlas. The latter will consist of the 40 weekly images and a series of satellite image animations that shows our living Earth from space. Satellite Eye for Galathea 3 is a project funded by Egmont Fonden and the participating institutes – Risø DTU, DTU Space, ESA Eduspace, Niels Bohr Institute at University of Copenhagen, GRAS and DMI - in the period 2006 to 2008. During the Galathea 3 expedition around 10.000 satellite images were collected along the entire route. The expedition took place from 11th August 2006 to 25th April 2007. The satellite images were shown in near-real-time on Google Earth along with near-real-time ship observations. Based on the satellite images, the ship observations and through collaboration with many Galathea 3 research projects educational material for upper secondary schools were being prepared. A total of 41 educational projects were being developed. Most of this information was published at EMU, the Danish portal for schools during 2007 in Danish and English. In addition, a satellite image with a short text was published each week at the homepage www.satelliteeye.dk . During 2007 the Satellite Eye team jointly with Nature & science prepared an educational film ‘Satellite Eye – Galathea 3 fra rummet’. This work is funded by The Danish Ministry of Education, Tips- og Lottopuljen. The film will be sent to upper secondary schools along with the Satellite Living Atlas. The latter will consist of the 40 weekly images and a series of satellite image animations that shows our living Earth from space.