January 2012:

Observed changes in top-of-the-atmosphere radiation and upper-ocean heating...

In an article published in Nature Geosciences we present an analysis of the heat entering our planet since 2000, measured at the top of the atmosphere by satellite instruments and down to a depth of 1800m within the world's oceans by automated profiling floats.

Despite an apparent break in the warming trend of the global ocean surface since the warm El Nino year of 1998 (see Figure, right), our analysis (lead by Dr Norman Loeb of the NASA Langley research centre) suggests that heat has continuing to build up at the rate of 0.5 Watts for each square metre of the Earth's surface - that is equivalent to the output of around 100,000 large power stations. This is important since it suggests that while surface warming appears to be absent over the last decade, energy continued to build up below the ocean surface, at a rate that is consistent with the effects of increased greenhouse gas concentrations in the atmosphere.

Global climate change results from an imbalance between the amount of sunlight absorbed by Earth and the thermal radiation emitted back to space. Elevated concentrations of greenhouse gases, due primarily to the burning of fossil fuels, have reduced the efficiency at which Earth can cool to space through thermal radiative emission, resulting in a positive energy imbalance. Once this excess energy enters Earth's climate, small amounts are used heating up the atmosphere and the land as well as melting ice, but the bulk enters the oceans which have the capacity to store vast quantities of energy. Therefore fluctuations in radiative energy entering at the top of Earth's atmosphere (see previous post) must vary in unison with changes in ocean heating rate.

The effects of El Niño and La Niña - the climatic phenomena affecting normal weather patterns across the tropical Pacific - are enough to disturb this steady build up of heat. Yet scientists had previously puzzled over additional "missing energy" that was detected entering the planet but which appeared not to arrive in the oceans. Our analysis suggest that changes to the way sea temperatures are measured, improvements in the satellite data products and substantial statistical margins of error are enough to account for this discrepancy. Furthermore, they confirm that energy has indeed been accumulating in Earth's climate since 2000 and that much of this "excess energy" has been continuing to heat the sub-surface ocean.

December 2011:

Winter floods in Britain are connected to atmospheric rivers

Work by David Lavers and co-authors has linked flooding in UK river catchements with distinct flows of warm, moist air termed moisture conveyors or Atmospheric Rivers (see New Scientist article).

These moisture conveyors carry large quantities of atmospheric moisture, the vast majority of which is invisible vapour, and this provides the fuel for intense precipitation. When moisture laden air masses are raised over mountains, the air cools and since cooler air carries less water vapour, rapid condensation of droplets can initiate heavy rainfall.

Over a period of a day or so, these heavy rainfall events can rain out much more water than is contained in each vertical column of air. This is only possible with the continual supply of moisture from further afield. In this work we have identified these warm, moisture conveyors or atmospheric rivers of moisture that supply large quantities of water vapour over a period of a few days. In the case shown in the Figure, this particular event caused substantial flooding in Cumbria.

Flooding will be particularly acute in catchments with rapid rainfall-river flow response times such as those found in the north and west of Britain. More results are described in the paper in Geophysical Research Letters

Since water vapour is almost certain to increase on average in a warming world, there are the implications that these events may become more severe and this is research that we are interested in conducting in the future. This research was conducted as part of the HydEF project funded through the Natural Environment Research Council's Changing Water Cycle program (read more on the departments Weather and Climate Discussion Blog).

October 2011:

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...

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.

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September 2011:

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.

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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:

The warm El Nino 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.

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