Earth Radiation Budget: Insights from GERB and future perspectives Imperial College London, University of Reading and the Geostationary Earth Radiation Budget (GERB) International Science Team GERB: the world’s only Earth Radiation Budget Instrument in Geostationary Orbit, providing observations every fifteen minutes and offering a unique perspective on the impact of rapidly varying parameters on the Earth’s energy balance GIST involves partners from UK, Europe and US but scientific lead is from Imperial College. Bi-annual joint science meetings with the US CERES team and the French/Indian Megha-Tropiques mission. Data record available from early 2004; third in a series of four instruments successfully launched in June, total mission lifetime projected to extend to at least 2018

Process studies: Impacts of cloud and aerosol Exploit synergy with narrow-band observations and high temporal resolution Partitioning of cloud radiative forcing by cloud type GERB Quantifying the radiative effect of mineral dust Tracking individual convective systems Dust optical depth (0.55 mm) LW Radiative Effect (W m-2) Systems originating over land are deeper and brighter. Ocean systems have a larger precipitating fraction Some examples of work that has been done looking at the radiative impact of specific climate components, exploiting the fact that we have temporally continuous coverage and additional ‘scene type’ information from co-located instrumentation. Red: Africa Blue: Atlantic

Model Evaluation - some examples of issues highlighted and quantified by GERB Comparisons with NWP output (SINERGEE) Discrepancies in the frequency, brightness and LW heating due to marine stratocumulus cloud – a key player in climate cloud feedback Desert albedo too high and dust storms not included Regional Climate Models Benefits for the forecast and climate modelling community. Many of the features seen in the (independent – i.e. not UKMO) regional climate model are also seen in the UKMO NWP model – improvements on the forecast timescale can potentially directly processes important at longer timescales. Tropical convection timing and duration over land incorrect –systematic errors of up to ~ 80 W m-2 Marine stratocumulus too bright

Observations also permit an assessment of model parameterisation schemes Near real-time comparisons provide a direct evaluation of NWP model upgrades... Top plots show the difference between GERB and UKMO NWP model OLR and albedo averaged over a specific domain for all-sky and clear conditions as a function of time. The effect of changes in model parameterisation schemes for convection and the boundary layer can be evaluated, as can changes to the surface representation. Many of these updates were implemented because of the issues identified in the previous slide. The bottom plot uses GERB OLR as an indicator of deep convection and looks at how the length scale associated with convective clusters evolves as a function of time of day. Bright areas show, for each data set, times when there are more storm systems than average at each length scale. The upward sweep in the observations indicates a tendency for smaller storms to cluster together and grow through the afternoon and early evening, something not seen at the 12 km scale (parameterised convection), but present at 4 km (parameterisation switched off). Using the OLR as a metric allows the model output to be sampled in a consistent manner to the observations. ...while focused high resolution studies in the CASCADE project suggest that explicitly resolving convection leads to a better representation of its diurnal cycle and the associated radiative impact

Future Opportunities with GERB The only broadband measurements that resolve the diurnal cycle are: A unique resource for climate & forecast model evaluation & development Quantifying the radiative impact of processes, on the timescales at which they vary: complementing current SEVIRI observations, and a future benefit to upcoming missions like EarthCare. Helping international efforts to quantify long-term variability in the global radiation budget Process based insights at the relevant timescale Allows routine evaluation of the impact of updates to data assimilation schemes: already proven benefits through the ad-hoc SINERGEE project, current interest from ECMWF and UKMO GERB provides an independent assessment of schemes used to merge broadband fluxes observed from polar orbit with those estimated from imagers in geostationary orbit: an ongoing effort – feeds through to longer-term studies investigating the variability in the global net radiation budget: fundamental climate metric. (BB GEO) (Polar BB + NB GEO) (Polar BB) Namibian stratus: SW flux diurnal cycle Enhanced products required by observational and modelling communities (e.g. clear-sky fluxes, monthly mean time-step means, dedicated process orientated products) requires a non-trivial effort and dedicated support