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Dr Adrian Lock

From affecting where patches of frost will form in winter to causing sudden showers, clouds affect our weather in a whole variety of ways. Clouds are also particularly tricky to forecast accurately, but research being carried out by Adrian Lock and the Boundary Layer Processes team aims to change that.

The boundary layer is the part of the atmosphere directly affected by the earth's surface. Typically, as the ground warms during the day, heat is transported up into the atmosphere as thermals. This warm updraft cools as it rises until the moisture it carries condenses into clouds.

But exactly where and when clouds form depends on atmospheric turbulence caused by the interaction between that warm and cool air. It is also affected by instabilities resulting from wind flow and how physical features on the earth's surface alter its course. As Adrian points out, these factors can make forecasting cloud cover extremely difficult.

"A lot of the issues that we have with weather forecasts is being able to tell whether a cloud is going to form or not," he says. "This strongly links to how the transport of heat and moisture in the boundary layer is dealt with by the representation of turbulence within the model."

Sunshine or showers?

The challenge of forecasting clouds, Adrian explains, is that they can occur on much smaller scales than can be represented by even the Met Office's highest resolution weather model.

"In the UK model you have grid squares that each represent an area of 1.5 km2. Even at that size it is still important to represent the effects of clouds that are too small to fill a grid square completely. To do that you need to know about the processes that cause those clouds to form."

A particular focus of Adrian's research is the formation of stratocumulus clouds - low level, thin clouds that are strongly influenced by atmospheric turbulence. Stratocumulus has a big impact on the climate we experience. In winter, they can act as a blanket and keep the surface relatively warm over night, which means forecasting them accurately is important for predicting surface temperatures and whether roads are likely to be icy.

To increase their understanding of how these processes vary from one place to another, Adrian's team is gathering detailed observations using weather instruments set up over an area of the countryside of just a few kilometres in size. They'll use this observational data to create a weather model representing that same area of countryside. If they can accurately represent real conditions at such a fine scale, Adrian says, "We can start to think about how we might do it better with the larger scale models currently used by the Met Office."

Clouds and climate change

Adrian's research into stratocumulus clouds has a global reach. Currently he's working with international research groups such as Global Atmospheric Systems Studies (GASS) and the Cloud Feedback Model Intercomparison Project (CFMIP). Together they are exploring how banks of stratocumulus clouds - that are persistent over large areas of the ocean - regulate our climate by reflecting sunlight back into space. They are also looking at whether global warming will cause those clouds to break up, and let more sunlight through.

To study this process, the groups use a very highresolution simulator called the Large Eddy Model (LEM) to look at how moisture and air temperatures are transported by turbulence in the boundary layer. The LEM uses an incredibly fine grid of just 50 x 50 metre squares to capture the atmospheric eddies caused by hot air rising or cool air falling. Adrian explains that the LEM forms part of a three-tier model comparison system: "It acts as a crucial tool between larger scale models such as the Met Office Unified Model and observations that were made at one specific point. It's a way of generalising our observations so we can back up the Unified Model and explore where it can be improved."

Capturing the imagination

Adrian's interest in the boundary layer began when, after joining the Met Office after finishing his maths degree, he was assigned to the boundary layer group. "I didn't know anything about it when I started, but I found the real world application of mathematical principles fascinating. I look out of the window and see the things I'm trying to represent in the weather model, like the wind rustling the treetops even when it's quite still at ground level."

After completing a PhD with the Met Office, Adrian went on to improve the parameters needed to represent this boundary layer, with a new framework that's been part of the UK weather model for almost 15 years. "To see a small contribution to the model performing well is something I'm really proud of," says Adrian. "But I've been looking for ways to move it forward ever since. There's always a different challenge to explore, and something new to learn."