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Studying Hector: meteorology and tracer transport

Explore how severe thunderstorm Hector influences water vapor in the UTLS using UKMO-UM and WRF models. Study focused on tracer transport processes with varying resolutions and parameterizations.

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Studying Hector: meteorology and tracer transport

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  1. Studying Hector: meteorology and tracer transport Maria Russo1, Charles Chemel2, John Pyle1 NCAS Climate, University of Cambridge NCAS Weather, University of Hertfordshire Manchester, 21 May 2009

  2. Overview • Hector case study 30 Nov ‘05. In collaboration with Charles Chemel • Models: WRF and UKMO-UM at 1km resolution • Impact of Hector on UTLS water vapour • Effect of resolution and convective parametrisation on the vertical transport of tracers • Model: UKMO-UM at 60, 12 and 1km • Using passive tracers with 6hr lifetime to study fast transport processes

  3. “Quantifying the imprint of a severe Hector Thunderstorm during ACTIVE/SCOUT-O3 onto the Water Content in the UTLS”Chemel et al., Monthly Weather Review, in press 1. Hector case study: 30 Nov ’05 • Horizontal resolution: 1km • Vertical resolution in UTLS: 100m for WRF and 500m for UM • Simulation started: 28 Nov for WRF, 29 Nov for UM • Initial and lateral boundary data: ECMWF for WRF, UKMet Office for UM

  4. Precipitation rate (mm/hr) Radar data WRF UM

  5. Hygrometeors CPOL Radar data WRF UM

  6. The effect of Hector on the water vapour in the UTLS Water vapour difference between 18:30 and 15:30 LT

  7. Conclusions • Hector was simulated with WRF and UM and results have been compared to observations • Both models get a realistic timing of convection but WRF overestimates precipitation while the UM underestimates it. • The top of the storm is similar in the 2 models, but the vertical distribution of hygrometeors is quite different. • In both models Hector produces a moistening of the UTLS, although the moistening is larger with the UM than with WRF

  8. Effect of resolution and convective parametrisation on the vertical transport of tracers GLOBAL FORECAST ~60km 12km 1km

  9. Experimental setup 0Z 3Z 0Z 3h 45h 28/11/2005 30/11/2005 • 3 hour spin-up followed by 45 hour run (48h in total) • Convection: parametrized for 12, 60km, explicit for 1km • Initial conditions are the same for all resolutions • LBC for 12 and 1km are derived from the global model run • 4 passive tracers with 6h mean lifetime: zero initial concentration + tracer concentration in its source layer is kept fixed throughout the run.

  10. Tracer 1: 45h mean profile Domain Storm ------- Rain ------- No-rain

  11. Tracer 2: 45h mean profile Domain Storm ------- Rain ------- No-rain

  12. Tracer 3: 45h mean profile Domain Storm ------- Rain ------- No-rain

  13. Tracer 4: 45h mean profile Domain Storm ------- Rain ------- No-rain

  14. Effect of tracer lifetime:

  15. Conclusions • The vertical distribution of tracers (and cloud ice) is very similar in 12 and 60 km model runs. • In the 1km model run, the surface tracers (1 and 2) are subject to less vertical transport compared to runs with parametrized convection, while tracer 3 and 4 reach higher than in the runs with parametrized convection. • Sampling at storm locations highlights the difference between average vertical transport and convective transport.

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