Latest News - Richard P. Allan
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University of Reading joins International Space Innovation Centre
Complex mathematical representations of Earth's atmosphere, oceans and land are required to make realistic predictions of future weather and climate. Satellite data is becoming increasingly important in evaluating and improving the physical representation of simulations of planet Earth that are made by these detailed computer models. For example, since 2003, Met Office weather forecast model simulations have been routinely scrutinised through comparisons with GERB satellite measurements of the Earth's radiative energy balance. Detailed analysis has been undertaken to understand and improve the simulation of cloud processes, examining the radiative properties of cirrus cloud from aircraft condensation trails and identifying the the greenhouse effect of desert dust.
As part of the commitment to the exploitation of satellite data in monitoring and measuring the workings of planet Earth's environment, the University of Reading has joined ISIC. Read more...Above: Radiative energy (units: Wm-2) emanating from planet Earth at 6am GMT on Monday 24 October 2011 as simulated by the Met Office global forecast model and the Geostationary Earth Radiation Budget (GERB) satellite instrument.
Dark regions in the image denote high altitude cloud, with cold tops that only weakly emit thermal infra-red (or longwave) radiative energy out to space. Relatively cloud-free, hot regions, such as Saudi Arabia in the image, emit strongly in the longwave part of the electromagnetic spectrum and appear light in the image above. This image was produced as part of the joint University of Reading and Met Office SINERGEE project (see article describing method), funded by the Natural Environment Research Council.
Intensified flows of moisture into the tropical rainy belt
Moisture is the fuel for tropical storms. Since they typically rain out in a day more water than is contained in the column of atmosphere, rain storms rely on a convergence of water vapour from surrounding regions. As part of the Natural Environment Research Council PREPARE project, work lead by project scientist, Matthias Zahn, has indicated an intensification of the inflow of moisture at low levels and outflow higher up in the tropical atmosphere over the last 2 decades (see Figure which depicts changes in moisture inflow into the tropical wet regions 1989-2008).
We found that detailed calculations every 6 hours were required to accurately follow the flows of moisture and our results have implications for the tropical water cycle and the intensity of rainfall. Further work is required to understand the changes in tropical circulation and its implications for changes in precipitation patterns. This work was published in the Journal of Geophysical Research.
Changes in Earth's radiative energy balance 1985-2010
In an article published in Meteorological Applications I put together the latest estimates of changes in the amount of energy entering the top of Earth's atmosphere. This comprises incoming sunlight, the outgoing reflected sunlight and the outgoing thermal emission of longwave radiation. The diagram below shows how this net flux changes from month to month (after removing the normal seasonal changes) based on satellite data (ERBS and CERES) and from reanalysis data which combines weather forecast models with observations:Estimates of near-global changes in (a) the net flux of energy into the top of the atmosphere (Net) and (b) the cloud radiative effect (NetCF) on this energy balance calculated by removing the simulated clear-sky fluxes (both in Watts per metre squared) since 1985 (the region considered is 60oS-60oN).
The warm El Niño years of 1998 and 2010 are characterised by negative departures from the norm. This is a result of natural shifts in the distributions of water vapour, cloud and surface temperature. Also prominent is a drop in net flux following the Pinatubo volcanic eruption in 1991 visible in the ERBS satellite data. Reflective particles called aerosol entering the stratosphere following the eruption increased the reflectivity of the planet (this is not seen in the reanalysis model since the volcano was not included and so the NetCF shows the influence of aerosol and cloud on the radiation balance; climate models can actually capture volcanic induced changes in the energy budget quite well).
Future work is endeavouring to understanding in more detail the bumps and dips in this graph which may tell us more about how the climate responds to small yet persistent radiative imbalances that determine whether our climate warms of cools. At present, human influences on the atmosphere have caused the Earth to receive more energy each year than it loses to space, resulting in a heating of the oceans.
Richard P. Allan Location: Department of Meteorology (2U15)