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New technique to better understanding of cloud behaviour developed

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Posted May 28, 2015

Scientists do not always need expensive specialized equipment to achieve new goals and to broader understanding of certain phenomenon. Scientists at University of California, Berkeley used two off-the-shelf digital cameras to collect three-dimensional data on cloud behaviour that have never been possible to collect before.  This method, called stereophotogrammetry provides unique window into clouds, thus improving climate models.

One of two cameras is being positioned to take images of clouds. Being a kilometre apart these cameras help to get 3-D images of clouds and measure their properties. Image credit: LBL

One of two cameras is being positioned to take images of clouds. Being a kilometre apart these cameras help to get 3-D images of clouds and measure their properties. Image credit: LBL

3-D images are created by two digital cameras situated about a kilometre apart facing Miami’s Biscayne Bay. This allows scientists to measure how fast the clouds rise. New data may help to better understanding about lightning rates, extreme precipitation to the ozone hole and improve global climate models. David Romps, a climate scientist who specializes in clouds, said that they are attempting to answer the most basic question – at what speeds do clouds rise through the atmosphere? Best technique to do that happens to be stereophotogrammetry.

Stereophotogrammetry uses photos to make 3D measurements of cloud boundaries. It was used before, but it always required a reference point, for example, mountain, building or other land-based object. New method does not require such reference point and allows using stereophotogrammetry to study clouds over the open ocean. This is very important, because scientists do not have many measurements from the clouds above the ocean, which appear to behave very differently than those above the land. Satellite data showed that continental areas light up with a lot of lightning and oceans less so.

Animation showing updraft of the cloud formations. Image credit: LBL

Animation showing updraft of the cloud formations. Image credit: LBL

Digital cameras spaces about 1 kilometre apart take pictures every 10 to 30 seconds, allowing scientists to look at the full lifecycle of clouds. This technique already provided some interesting results. Using stereophotogrammetry, scientists have measured the speeds of shallow clouds rising through the atmosphere at 1 to 3 meters per second and of deeper clouds rising at speeds in excess of 10 meters per second. These updraft speeds can impact lightning rates, as faster clouds tend to produce more lightning and play an important role in the microphysics, general precipitation, and aerosol processing, which all impact climate simulations.

If clouds are moving upwards fast enough they can penetrate the stratosphere, throwing out water vapour and ice. This sets the humidity of the stratosphere, and that has an impact both because water vapour is greenhouse gas and also because water vapour, through a sequence of events, has an effect on the ozone hole. Clouds, in fact, are the largest source of uncertainty in today’s climate models, because scientists are still seeking a fundamental theory for moist convection.

David Romps  said that knowing speed of clouds “is important for several reasons; the important one is that we lack a really basic understanding of what processes control these clouds, the levels they peter out at, and how buoyant they are.” Stereophotogrammetry can provide very useful information in this quest of achieving more accurate parameterizations of clouds that go into global climate models.

However, a lot more work needs to be done. Stereophotogrammetry has been a labour-intensive process, but scientists are already using new algorithms and supercomputers to make this work easier and faster. Next step is to compare new data from stereophotogrammetry to other sources of information to answer basic questions about cloud life cycles. Scientists are particularly interested in understanding what environmental conditions can be used to forecast the sizes, speeds, depths, and lifetimes of convective clouds. Their achievements will better understanding about global climate.

Source: LBL

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