studying hector: meteorology and tracer transport

CentreCentre for for Atmospheric Science Atmospheric Science

Studying Hector: meteorology and Studying Hector: meteorology and tracer transport tracer transport

Maria Russo1, Charles Chemel2, John Pyle1

1.NCAS Climate, University of Cambridge

2.NCAS Weather, University of Hertfordshire

Manchester, 21 May 2009


Overview

1. 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

2. 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


“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


Precipitation rate (mm/hr)

Radar data

WRF

UM


Hygrometeors

CPOL Radar data

WRF

UM


The effect of Hector on the water vapour in the UTLS

Water vapour difference between 18:30 and 15:30 LT


Conclusions

1. Hector was simulated with WRF and UM and results have been compared to observations

2. Both models get a realistic timing of convection but WRF overestimates precipitation while the UM underestimates it.

3. The top of the storm is similar in the 2 models, but the vertical distribution of hygrometeors is quite different.

4. In both models Hector produces a moistening of the UTLS, although the moistening is larger with the UM than with WRF


Effect of resolution and convective parametrisation on the vertical transport of tracers

GLOBAL FORECAST ~60km

1km

12km


Experimental setup

• 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.

TRACER1 TRACER2 TRACER3 TRACER4

Source layer ~0-500m ~2-4km ~4-6km ~14-16km

28/11/2005

0Z 3Z 0Z

30/11/2005

45h 3h


Tracer 1: 45h mean profile

1km 12km 60km

Domain

Storm

------- Rain

------- No-rain



1km 12km 60km

Domain

Storm

------- Rain

------- No-rain



Domain

Storm

------- Rain

------- No-rain

1km 12km 60km


Effect of tracer lifetime:


Conclusions

1. The vertical distribution of tracers (and cloud ice) is very similar in 12 and 60 km model runs.

2. 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.

3. Sampling at storm locations highlights the difference between average vertical transport and convective transport.

studying hector: meteorology and tracer transport

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