1. COLPEX; Cold Air Pooling over Complex Terrain Bradley Jemmett-Smith 1 st year PhD RMets Conference 10 th July 2010

2. Overview Introduction to what Cold Air Pooling is:  Ideal conditions  In-situ cooling versus cold pool drainage The rationale behind the project COLPEX field campaign Preliminary results:  Observations from the COLPEX field campaign  High resolution model output from the Met Office Unified Model Summary Questions

3. What is Cold Air Pooling? Cold Pool occurrences are characterised by a temperature inversion, with cooler temperatures at lower levels. Ideal conditions are:  A stable/static atmosphere with no cloud cover.  Low wind speeds above the valley. Develop soon after sunset and breakdown following sunrise.

4. What is Cold Air Pooling? (Gustavsson et al, 1998)(Borgren et al, 2000) Cold Pool occurrences are characterised by a temperature inversion, with cooler temperatures at lower levels. Ideal conditions are:  A stable/static atmosphere with no cloud cover.  Low wind speeds above the valley. Develop soon after sunset and breakdown following sunrise.

5. Two mechanisms:  Drainage flows forced by radiative cooling on sloped surfaces which pool at the valley bottom.  In-situ radiative cooling and sheltering within the valley. What is Cold Air Pooling? WHICH IS MORE DOMINANT?

6. Cold pools are associated with high impact weather events such as fog and frost. Pollution episodes through the stagnation of air also give rise to health issues. Total economic losses related to fog alone can be comparable to those from other weather events such as tornadoes and hurricanes (Gultepe et al, 2007). Current representation of maximum/minimum temperature related to Cold Air Pooling in National Weather Prediction models is poor. Understanding the exact timing of formation and break-up of Cold Air Pools is lacking. Very few investigations previously on scales < 1km, only METCRAX (Meteor Crater Experiment) (Whiteman et al, 2006). Better representation of Cold Air Pools will improve regional weather prediction. Who will benefit?

7. England Shropshire Clun Valley (Map images ©2010 Google) COLPEX Field Campaign

8. Collaboration between the University of Leeds, the University Salford and the Met Office. Comprehensive field campaign from June 2009 – April 2010, based in the Clun Valley region Shropshire, UK. Instruments include; 3 x flux towers, 10 AWS, 20 x HOBOs, Lidar and radiosonde launches. COLPEX Field Campaign (Map copyright of the Met Office)

9. Preliminary Results : Case Study 04/03/2010

10. Preliminary Results : Case Study 04/03/2010

11. Summary Ultimate aim is to improve cold pool forecasting, this will be achieved through both observations and model investigations and comparisons. Successful field campaign concluded in April 2010. High resolution Model studies using the Met Office UM have recently begun, looking at Intense Observation Periods (IOP’s) conducted during field campaign. Preliminary results are encouraging, much to be done…….