Jennifer Catto Supervisors: Len Shaffrey – NCAS Climate and Kevin Hodges - ESSC The Representation of Extratropical Cyclones in HiGEM

Outline Motivation Description of HiGEM Composites – Methodology – Results – Horizontal + Vertical Structure – Lifecycles Conclusions

Motivation Want to be able to represent climatology and structure of extra-tropical cyclones because; – Important for large-scale flow in transporting heat and moisture, – Huge socioeconomic impacts, – Want to be able to forecast how they will change in the future. Important to consider what the storms that the tracking is picking up actually look like – do they show the features of extratropical cyclones? – Structures important for regional climate impacts – strong winds and heavy rain have large socioeconomic impacts.

HiGEM & ERA-40 HiGEM – Atmosphere Based on HadGEM1 1.25° lat x 0.83° lon (N144) 38 vertical levels – Ocean 1/3° x 1/3° 30 levels – Land Surface – Dynamic Sea Ice – 50 years of present day control run excluding 20 years spin up time. ERA-40 – Approximately 1.1 ° x 1.1 ° – 45 years of data Storms found and tracked using Kevin Hodges’ tracking algorithm.

Composite Analysis - Methodology Step 1: Identify tracks using Kevin’s tracking program

Composite Analysis - Methodology Step 2: Choose at what stage in the lifecycle to composite the tracks e.g. – Maximum tendency – Maximum intensity – Maximum precipitation – Minimum pressure and identify where this occurs

Composite Analysis - Methodology Step 3: Extract the 20 o radius around this point and note the direction of propagation of the storms.

Composite Analysis - Methodology Step 4: Rotate these areas to the same direction of propagation and average them. + + =

Conceptual Models

Results – horizontal winds Colours – system relative wind speed (m/s)

Results – horizontal winds Colours – system relative wind speed (m/s)

Results – horizontal winds Colours – system relative wind speed (m/s)

Results – vertical slice along WCB

Results – vertical winds ERA-40 HiGEM Colours – vertical velocity (hPa/hour)

Results – Relative Humidity ERA-40 HiGEM Relative Humidity at 500hPa (%)

Conclusions – HiGEM does a very good job of representing the structures of extratropical storms when compared to ERA-40. – The warm conveyor belt, cold conveyor belt and dry intrusion can be identified (to some extent) in the composite storms.