2008 report
Progress: 40%
1. Work done and achievements made
The work during the last year concerns experimental studies (observations) including satellite data, analyzing previous Arctic data sets (collected prior or unrelated to DAMOCLES), analysis of reanalysis data and modelling studies.
The first major field experiment was carried out with intensive continuous meteorological observations by UT at the Tara drifting ice camp. Synoptic observations from R/V Polarstern during late summer 2007 (AWI) and an aircraft campaign in March 2007 near Svalbard (AWI). Furthermore, aerosol observations were carried out from R/V Oceania over the North Atlantic Ocean.
The main DAMOCLES effort was the Tara ice drift experiment, with an emphasis on boundary-layer structure (WP2.2) but also with importance for WP2.3. Soundings were made with a tethered system, generating in all 95 profiles over 35 days, including three full 24-hour periods. Surface radiation was also measured continuously; FMI and FIMR contributed to the planning radiation measurements. Additionally, rawinsonde data and routine meteorological observations, including radiation fluxes and cloud cover observations, will soon be available from Polarstern expedition ARKXXII/2, which was carried out by AWI to the inner Arctic between end of July and end of September 2007.
AWI has made available datasets for DAMOCLES, obtained during the previous AWI aircraft based campaigns REFLEX and ARTIST (Deliverable D2.3-1). Flights were carried out during these campaigns in the cloud-topped polar boundary layer over the ice covered Barents Sea and Fram Strait near Svalbard. Data consist of mean atmospheric variables (wind, temperature, humidity) and of turbulent and radiative fluxes partly within clouds. SU has made the meteorological data set from the Arctic Ocean Experiment 2001 (AOE-2001) available to the DAMOCLES community (Deliverable D2.3-3), as a temporal substitute for the Arctic Summer Cloud-Ocean Study (ASCOS) data, which will come one year later than originally planned due to factors outside of our control, see below. This data contain observations of Arctic summer boundary layer and cloud vertical structure, boundary-layer fluxes as well as regular weather station observations. These datasets can be used for process studies with mesoscale models and for the test of parameterizations. SU has also finalized the analysis of ARCMIP model simulations for the SHEBA year (Deliverable 2.3-2). The main conclusions can be summarized in winter clouds being too optically thin for longwave radiation, while summer clouds are modelled too optically thick for shortwave radiation. Both discrepancies are believed to be related to Arctic cloud microphysics and aerosol climate being different to that at more southerly latitudes. The results were summarized in a manuscript that was tentatively accepted by the Journal of Applied Meteorology and Climatology.
UB has continued the work with satellite retrievals of cloud parameters. Version 0 of the cloud liquid water (CLW) retrieval is an integrated retrieval of cloud liquid water (CLW), total water vapour, sea-surface wind speed, surface temperature and ice cover from data of AMSR-E (Advanced Microwave Scanning Radiometer, on the satellite Aqua). It uses a maximum a posteriori (optimal estimation) inverse method (see, e.g., Rodgers, "Retrieval of atmospheric temperature and composition from remote measurements of thermal radiation," Rev. Geophys. & Space Phys. 14(4), 609-624, 1976). This algorithm was originally developed and implemented at DTU, and has then been adapted to and integrated into the software infrastructure at UB. First test runs have been completed by UB.
FMI has carried out modelling studies of warm-air advection over Arctic sea ice (also see report to Task 2.2). Considering Task 2.3, attention was paid to cloud formation and associated changes in radiative transfer. The operational weather prediction model HIRLAM suffered from excessive moisture and cloudiness in the atmospheric boundary layer, but investigations demonstrated that during warm-air advection, the reasons for this were not related to air-ice exchange in the Arctic but to excessive moisture at the lateral boundary conditions over the open ocean. A two-dimensional research model with boundary conditions prescribed according to aircraft observations did not suffer from excessive moisture. A manuscript has been submitted to Tellus (see Task 2.2.)
FIMR and FMI also studied the precipitation, cloud cover and radiative fluxes over the Arctic Ocean based on the NCEP/NCAR reanalysis and ECMWF operational analyses. The objective was to validate the applicability of these data as forcing for thermodynamic sea ice models. In addition, the effect of surface albedo on sea-ice mass balance has been studied. The modelling experiments were carried out using CHINARE2003 and SHEBA data sets. On seasonal scale, from May to September, the NCAR/NCEP air temperature is warmer than that of the ECMWF operational forecasts, while during the ice melting period the ECMWF air temperature is slightly warmer. For seasonal variation during CHINARE2003, ECMWF and NCEP/NCAR results are in general comparable, except that the NCAR/NCEP precipitation is much larger than in the ECMWF. The ECMWF operational analyses have better quality to drive the HIGHTSI model to produce reasonable results than the NCAR/NCEP re-analysis. The surface albedo, which is parameterized as function of snow and ice thickness is important for ice mass balance, particularly during the onset of snow melting. An improvement of surface albedo parameterization scheme is even more essential than to reduce the uncertainties of precipitation in the external forcing. A manuscript summarizing these results has been submitted to Journal of Geophysical Research.
Planning for the Arctic Summer Cloud-Ocean Study on the Swedish icebreaker Oden has moved into an operational phase. Funding is in place for all components, including for an aircraft based component (AMISA) in collaboration with NASA where the NASA P-3 research aircraft will fly six missions from Svalbard to the ASCOS ice drift location. The experiment will focus on boundary-layer clouds from physical, chemical and aerosol points of view, with an extensive measurement program on the icebreaker with various remote sensing instruments including cloud and wind radars and lidars, atmospheric chemistry and aerosol observations. Measurements on the ice include surface fluxes under and above the ice and various sounding instrumentation. A special emphasis of the planned activities is on the transition from summer to autumn freeze-up conditions. The expedition is currently planned for late July through mid-September, 2007.
