ASET (Atmosphere Sea ice Exchanges and Teleconnections)
Over the last decades, the Arctic sea ice has experienced a drastic decline which is expected to continue in the near-term future. Arctic changes are thought to impact the mid-latitude atmospheric circulation to an extent and through mechanisms which are still highly debated. Heat exchange between sea ice and atmosphere plays a crucial role on the rate of Arctic sea ice melting (Rothrock et al, 1999 ; Screen and Simmonds, 2010) as well as on the teleconnections between polar and non-polar regions (Bader et al 2011 ; Vihma, 2014 ; Overland et al 2015). Lower troposphere heating through turbulent heat fluxes (latent and sensible) dictate the thermal structure of the lower atmosphere and plays a key role in the development of atmospheric circulation anomalies (Overland, 2015).
The representation of surface turbulent fluxes of sensible and latent heat at the ice-atmosphere interface is relatively crude in most climate models. They are typically estimated using bulk formulas (e.g. Roy et al, 2015), based on Monin-Obukhov similarity theory (e.g. Andreas 2002 ; Andreas et al, 2010a,b). Most of the existing formulations, however, have been developed exploiting observational campaigns which took place in the tropics or the mid-latitudes (e.g Belamari and Pirani 2007) and are not necessarily suitable for the particular conditions found in polar regions (e.g. high stability of the atmospheric profile, surface roughness). Formulations developed specifically for polar conditions rely on sparse observational data and still lack an accurate formulation of the stability functions appropriately accounting for high stability and surface roughness (e.g. Andreas 2002 ; Andreas et al, 2010a,b ; Lupkes et al, 2012, 2013). The transfer coefficients are therefore often instead assumed to be constant over sea ice (Parkinson and Washington 1979 ; Maykut, 1982) in state-of-the-art climate models. The lack of available observations is the main reason for the lack of more advanced or suitable parameterisations, together with the insufficiently detailed simulated surface roughness.
The Year of Polar Prediction (YOPP) was an extended period (2017-2020) of coordinated intensive observational and modeling activities aiming at improving polar prediction capabilities. YOPP was a WCRP/WWRP (World Climate Research Programme / World Weather Research Programme) initiative as part of the Polar Prediction Project and provided an opportunity to gather a wide variety of new observations in the polar regions. The ASET project offers to improve the realism of modelled Arctic climate changes and linkages between polar and mid-latitude regions through the development of novel formulations of turbulent heat exchanges between the atmosphere and sea ice, exploiting the wealth of YOPP new observations.
1. The first objective is to build a database documenting as extensively as possible the atmosphere-ice interface and heat exchanges from the YOPP-endorsed and previous campaigns.
2. The second is to develop new parameterisations for the latent and sensible heat fluxes at the ice surface exploiting the YOPP data.
3. The third is to improve our understanding and refine estimates of the Arctic climate change and its impact on the midlatitudes, exploiting model improvements from ASET.
... still in progress ...