Joint Seminar: Convective cloud-cloud interaction, memory, and precipitation extremes

Observational evidence points to an increase of convective precipitation intensity with temperature beyond the Clausius-Clapeyron rate of 7%/K [1-6], ruling out basic thermodynamics as a null-model. Here we perform large eddy simulations (LES) of the convective dynamics by imposing an idealized diurnal cycle of surface temperature. Convective events interact and self-organize, increase in intensity and area throughout the day, and largest intensities occur far later than the peak in rain area. By tracking events, we follow event histories throughout their life cycles, and find that colliding events react strongly to changes in boundary conditions, e.g. increased surface temperature, while solitary events remain unaffected. Intensication can also be reached by unchanged mean temperature but allowing more time for self-organization. This suggests, that the convective field as a whole acquires a memory of past precipitation and inter-cloud dynamics, driving precipitation intensity. Together, our results imply that convective precipitation intensities result from dynamical interactions between clouds and temperature increase is only one way how greater interaction can be achieved. The findings may have implications for the diurnal cycle of convection and its parameterization in large scale models.

 

References:
[1] G. Lenderink and E. van Meijgaard. Increase in hourly precipitation extremes beyond expectations from temperature changes. Nature Geosci., 1:511-514, 2008.
[2] R. Hardwick Jones, S. Westra, and A. Sharma. Observed relationship between extreme subdaily precipitation, surface temperature and relative humidity. Geophys. Res. Lett., 37:5 pp.,
2010. doi: 10.1029/2010GL045081.
[3] N Utsumi, S Seto, S Kanae, E E Maeda, and T Oki. Does higher surface temperature intensify
extreme precipitation? Geophys. Res. Lett., 38:5 pp., 2011. doi: 10.1029/2011GL048426.
[4] Peter Berg, Christopher Moseley, and Jan O Haerter. Strong increase in convective precipitation
in response to higher temperatures. Nature Geosci., 6:181-185, 2013.
[5] Geremy Panthou, Alain Mailhot, Edward Laurence, and Guillaume Talbot. Relationship between surface temperature and extreme rainfalls: A multi-time-scale and event-based analysis.
Journal of Hydrometeorology, 15(5):1999-2011, 2014.
[6] P Molnar, S Fatichi, L Gaal, J Szolgay, and P Burlando. Storm type effects on super clausius-clapeyron scaling of intense rainstorm properties with air temperature. Hydrology and Earth
System Sciences, 19(4):1753-1766, 2015.

Date

09.09.2015

Time

13:30 h

Place

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

Speaker

Jan Härter, Niels Bohr Institute, Copenhagen

Organizers

Stefan Bühler

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