Posts Tagged ‘Convection’

Storms and climate change

March 25, 2010

I’ve been pretty distracted recently with the Institute of Physics issue. I’ll hopefully draw that chapter to a close in the next couple of weeks (it looks like the IoP are going to stick their head in the sand and wait for it to blow over) but right now I’m bringing my current project to a close so I thought I’d look at how that work has gone and where it’ll go in the future.

The work I’ve been doing at Manchester over the last few years is looking at how storms form – the kind of storms that lead to floods like the one seen in Boscastle in 2004.

These type of storms are pretty difficult to forecast because they are often smaller than the computer model grid box size that such models use to chunk up the atmosphere into a more manageable mathematical problem. I spoke about this in a recent edition of the NERC Planet Earth podcast.

I’ve been part of a couple of big projects that try and observe these storms as they form. We do this by getting big teams of scientists, around 50 or so, to go to a certain location for a few months and then use surface stations, aeroplanes, weather balloons, radar, lidar and satellite data to get a really good picture of what’s going on.

The video below shows the Chilbolton radar scanning convective clouds as they develop whilst someone launches weather balloons in the bottom left hand corner – this is pretty typical of what goes on at several locations during these campaigns, although this is the biggest dish we’ve used.

I’ve only been looking at a small part of the storm problem: how does air that descends from the stratosphere influence these storms?

I’ve shown that this upper-level air can sometimes make storms less likely by introducing thin layers into the atmosphere that can cap storms before they get going (Russell et al., 2008) and sometimes make storms more likely by changing the temperature structure of the atmosphere to make the convection more powerful (Russell et al., 2009).

That doesn’t sound much like progress, does it? Well, now that we know a lot more about these two types of effect, we can start to generalise them and use that knowledge to help forecasters improve their predictions and computer models. This is what we are working on now.

So how does climate change fit in to all this?

The next big step in this work is to try and define a “storm environment”, including what we now know about these upper-level features, and apply this to the kind of projections that climate models produce. These projections use even bigger grid boxes than weather models so this step will not be easy but if we can show that this method works using the data that is available now (and hope for better resolution soon) then we can start to think about the likely changes in this storm environment. These big storms can really affect people’s lives so this type of work is something that would influence how we start to prepare for the future.

References:

ResearchBlogging.orgRussell, A., Vaughan, G., Norton, E., Morcrette, C., Browning, K., & Blyth, A. (2008). Convective inhibition beneath an upper-level PV anomaly Quarterly Journal of the Royal Meteorological Society, 134 (631), 371-383 DOI: 10.1002/qj.214

ResearchBlogging.orgRUSSELL, A., VAUGHAN, G., NORTON, E., RICKETTS, H., MORCRETTE, C., HEWISON, T., BROWNING, K., & BLYTH, A. (2009). Convection forced by a descending dry layer and low-level moist convergence Tellus A, 61 (2), 250-263 DOI: 10.1111/j.1600-0870.2008.00382.x