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Harm Jonker Harry Van den Akker

A statistical approach to the life cycle analysis of cumulus clouds selected in a virtual reality environment. Eric Griffith Frits Post Michal Koutek. Harm Jonker Harry Van den Akker. Thijs Heus (thijs.heus@zmaw.de). J. Geophys. Res. 2009. Life cycle of cumulus clouds.

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Harm Jonker Harry Van den Akker

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  1. A statistical approach to the life cycle analysis of cumulus cloudsselected in a virtual reality environment Eric Griffith Frits Post Michal Koutek Harm Jonker Harry Van den Akker Thijs Heus (thijs.heus@zmaw.de) J. Geophys. Res. 2009

  2. Life cycle of cumulus clouds • Life cycle effects are often a bias in statistics • Not that much observational time-dependent data present; how can we be even sure that the definition of non-decaying clouds in airplane observations is correct? • LES should be perfect tool with complete datasets: Select a large number of clouds to analyze in time, e.g. conditional sampling over life stage. 2

  3. Pulsating growth • Observed in reality and/or models by Malkus(1952), Grinnel(1996), French(1999), Blyth(2005), Zhao & Austin (2005),… • All are studies on limited amount of clouds • Why does this pulsating growth happen anyway? 8

  4. Cloud Selection • Create 4D, high-res data sets in DALES • Visualize in Virtual Reality (thanks to Eric Griffith et. al.) • 35 exemplary clouds from BOMEX, plus quite some from other cases selected => Possibility of statistics 9

  5. Mean cloud statistics 10

  6. tp = 408s Cloud properties in height and time 11

  7. W versus t/z • Inside the cloud Around the cloud 12

  8. Cloud lifecycle means 15

  9. The composite pulse • The pulse is the building block of the cloud • A pulse is defined here as the distance between 2 minima in liquid water at 800m • The average lifetime of a pulse tp=408s • Composition over 140 pulses 16

  10. Pulse Properties 17

  11. No Pulsating signal from the sub cloud 19

  12. Mass flux and Lateral entrainment The buoyancy precedes the massflux, that precedes the horizontal divergence 20

  13. Ye Olde Cloud top/lateral mixing controversy 21 Heus et al., JAS 2008

  14. 24

  15. Conclusions • Pulse based statistics capture much more of the cloud dynamics than cloud based statistics • Pulses are independent of subcloud and mesoscale, but due to massive entrainment below the ascending pulse top • The APT creates a detrainment/entrainment pattern that may resemble cloud top entrainment for the first pulse, but is effectively lateral mixing after this initial phase 25

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