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HAIC WP5.2: Natural ice crystals. Part 1 : Individual ice crystal properties in convective cloud systems (tropics, mid latitude, oceanic, continental,…). Alfons Schwarzenboeck*, Christophe Duroure*, Régis Dupuy*. * Laboratoire de Météorologie Physique: http://wwwobs.univ-bpclermont.fr/atmos.

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  1. HAIC WP5.2: Natural ice crystals Part 1 : Individual ice crystal properties in convective cloud systems (tropics, mid latitude, oceanic, continental,…) Alfons Schwarzenboeck*, Christophe Duroure*, Régis Dupuy* *Laboratoire de Météorologie Physique: http://wwwobs.univ-bpclermont.fr/atmos

  2. HAIC WP5.2: Natural ice crystals Ice particle growth regimes in convective clouds • Identification of crystal growth mechanisms after nucleation with subsequent: • a) vapor diffusion b) aggregation and/or c) riming • (pristine crystal), (snowflake), (graupel, hail). • Pure riming growth regimes (graupel and hail) in convective cores (often not sampled) of MCS systems and pure aggregation regimes (snowflakes) in more stratiform parts are hardly observed. • Larger hydrometeors in convective cloud systems seem to be the result of a complex mixture of riming and aggregation processes, even far away (few hundred of kilometers) from convective regions. • Compared to mid latitude convective systems, tropical MCS evidencesomewhat well mixed growth histories of hydrometeors on a mesoscale : riming-aggregation continuum.

  3. HAIC WP5.2: Natural ice crystals Crystal growth in convective clouds dominated by 3 major growth mechanisms: - aggregation ( crystal concentration.,..) - diffusion ( ice supersaturation, temp…) - riming ( existing crystals,  important supercooled droplet concentration.,..) Aggregation Diffusion Riming CPI (cloud particle imager): data CNRS-LaMP

  4. HAIC WP5.2: Natural ice crystals Data from HYMEX: Mid-latitude convection & high precipitation on 15/10/2012 Diffusion-aggregation domain 500 µm • Clouds can show mixing of crystals, having experienced different growth regimes for the same size (500µm here). The two ice crystals shown here (CPI images) have grown by pure vapor diffusion (left) and aggregation (right) of smaller crystals that originally had grown by vapor diffusion. • Crystal growth in the diffusion-aggregation plan is often observed in isolated strong convective cells.

  5. 2 mm HAIC WP5.2: Natural ice crystals Megha-Tropiques 2010 over West Africa: MCS type convection • Continental MCS type convection! Note that a simple MCS definition with only one convective and one stratiform region may not be realistic. • MCS type ice crystals predominantly in the riming-aggregation domain. • Transition can be observed at small scales (MT1-flight20,T= -7°C, D=5 Km) . Riming-aggregation domain PIP (precipitation imaging probe): data CNRS-LaMP • Crystal growth predominantly observed in the diffusion-aggregation plane is not the case in large Mesoscale Convective Systems (MCS) were riming plays a more dominant role! • Variable growth modes in convective systems: The smaller the ice crystals the more its growth is dominated by vapor diffusion, whereas the larger ice crystal growth is dominated by riming or aggregation..

  6. HAIC WP5.2: Natural ice crystals Megha-Tropiques 2011 over the Indian Ocean: Oceanic convection: partly MCS type, partly isolated convection Primary & secondary diffusional growth CPI (cloud particle imager): data CNRS-LaMP • Secondary crystal growth known as capped columns: primary column (initial growth at T<-20°C) and secondary growth of mostly plates (at approximately temperatures of -10°C) or sometimes side stellars (higher supersaturation than for side plates). Capped columns (secondary plates on both end of primary column) are frequently observed in convection over ocean.

  7. HAIC WP5.2: Natural ice crystals Part 2 : Crystal parameterization crystal geometry parameters crystal size (PSD, MMD) ice density

  8. Physical parameters HAIC WP5.2: Natural ice crystals Crystal geometry: • Length or Dmax • Width • Area • Perimeter Length or Dmax Center of Gravity Width

  9. PSD: crystal size occurrence HAIC WP5.2: Natural ice crystals The occurrence of ice crystal physical parameters (size & number) is shown on the cloud particle size distribution (PSD). • PSD trends as a function of Dmax of the particles observed during the two measurement campaigns of Megha-Tropiques: • MCS above Indian Ocean” (November 2011). • Isolated convection above the Indian Ocean (December 2011). • MCS above African continent (August 2010).

  10. HAIC WP5.2: Natural ice crystals Crystal density Median mass diameters, ice density expressed in m(Dmax) relationships for continental & oceanic convection Will come in very few weeks: we are re-evaluating the available data sets for final MMD diameters and m(Dmax) averaged relationships to be published

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