Radiative influences on glaciation time scales in mixed phase clouds
Download
1 / 13

Radiative Influences on Glaciation Time-Scales in Mixed-Phase Clouds - PowerPoint PPT Presentation


  • 110 Views
  • Uploaded on

Radiative Influences on Glaciation Time-Scales in Mixed-Phase Clouds. Zachary Lebo, Nathanial Johnson, and Jerry Harrington Penn State University Acknowledgements: DOE-ARM and Dennis Lamb for many useful discussions. Why Can Liquid and Ice Persist in Mixed-Phase Clouds?.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Radiative Influences on Glaciation Time-Scales in Mixed-Phase Clouds' - ulla-sears


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Radiative influences on glaciation time scales in mixed phase clouds

Radiative Influences on Glaciation Time-Scales in Mixed-Phase Clouds

Zachary Lebo, Nathanial Johnson, and

Jerry Harrington

Penn State University

Acknowledgements: DOE-ARM and Dennis Lamb for many useful discussions.


Why Can Liquid and Ice Persist in Mixed-Phase Clouds? Mixed-Phase Clouds

Previous work has shown:

  • Cloud tops can maintain narrow liquid layers if ice crystals remain small and updrafts are sufficiently strong (Rauber and Tokay, 1991)

  • It is possible to maintain a mix of liquid and ice during ascent (Tremblay et al., 1996)

  • Liquid topped arctic clouds that precipitate ice are possible if ice nuclei concentrations are small (Pinto, 1998, Harrington et al., 1999) and if ice nuclei are removed through sedimentation (Harrington and Olsson, 2001, Morrison et al., 2005).


Glaciation time scales
Glaciation Time-Scales Mixed-Phase Clouds

  • Hence, time-scalefor complete glaciation of mixed-phase clouds is important and depends on (at least):

    • Ice concentration and updraft velocity

  • Since radiation affects the growth of drops, is there a similar influence on the Bergeron process?

160 min ~ 2.6 hrs

16 min

1.6 min

From Korolev and Isaac (2003)


Radiatively modified ice growth
Radiatively Modified Ice Growth Mixed-Phase Clouds

  • Method is that of Korolev and Isaac (2003) but add the radiative term for the growth of ice:

Radiative Effect = Ed

  • Start with a simple box model

    • Integrate above equation numerically until a fixed amount of cloud liquid water content (LWC) is depleted.


Computing radiative influence
Computing Radiative Influence Mixed-Phase Clouds

  • Use simple, static adiabatic model of stratiform arctic cloud.

  • Solar (SW) and infrared (LW) radiative heating computed via two-stream model(Harrington and Olsson, 2001)


Radiative heating cooling of crystals
Radiative Heating/Cooling of Crystals Mixed-Phase Clouds

Ed At Cloud Top

Plate Crystals

  • Ed easily computed at each vertical level within the idealized cloud.

  • LW Cooling: Increases rapidly while SW Heating increases more slowly with size.

  • Net Effect: LW dominates at small sizes with cross-over to net heating at large sizes


Radiative influences on ice supersaturation
Radiative Influences on Ice Supersaturation Mixed-Phase Clouds

  • Cloud Top: Radiative cooling dominates, sui increases to over 30% from ~ 15%

  • Mid Cloud: SW heating dominates decreasing sui to less than 15%.

    • When SW Heating becomes large enough  Crystals will actually sublimate

Crystal

Sublimation

Crystal

Growth

Plate Crystals

Ni = 1 L-1

Ttop = -15 C

q0 = 450


Radiative influence on glaciation time scale
Radiative Influence on Glaciation Time-Scale Mixed-Phase Clouds

  • No Radiation: Results similar to Korolev and Issac.

  • LW Cooling: Drastic decrease in glaciation time

    • Positive feedback: Larger crystals, more cooling, etc.

  • SW Heating: Reduces LW effect at cloud top.

Initial LWC: 0.1 g m-3

Ni = 1 L-1

Plate Crystals


Radiative influence on glaciation time scale1
Radiative Influence on Glaciation Time-Scale Mixed-Phase Clouds

  • LW Cooling drops off rapidly.

    • 100 m below cloud top glaciation time-scales not at strongly impacted.

  • Mid-Cloud: Since SW heating dominates, glaciation does not occur.

    • Crystals grow to radiatively limited sizes.

Initial LWC: 0.1 g m-3

Ni = 1 L-1

Plate Crystals


Glaciation time scale fixed rates
Glaciation Time-Scale: Fixed Rates Mixed-Phase Clouds

No Radiation

  • Crystals grow too large in box model

    • Fix ice growth rates at a particular size

  • Small crystals, glaciation time is long  radiative influences don’t matter

  • Larger crystals, glaciation times shorter (< 100min) so radiative influences quite important.


Concluding remarks
Concluding Remarks Mixed-Phase Clouds

  • Simple box model calculations suggest that radiative heating and cooling may substantially influence glaciation times.

    • LW cooling at cloud top may enhance crystal growth

    • SW heating (even when weak) may substantially increase mixed-phase cloud lifetimes (as long as q0 > 750)

  • Computations with bin microphysical model tend to corroborate these results.

  • Next plan to incorporate into parcel models, and LES, to test radiative influences on more realistically simulated clouds.


Stratiform arctic mixed phase persistence
Stratiform Arctic Mixed-Phase Persistence Mixed-Phase Clouds

LES-Derived Water Paths

  • In the Arctic: Mixed-phase clouds occur throughout the year.

  • Ice nuclei ice concentration (& size) Important for mixed-phase longevity(Pinto, 1998; Harrington et al., 1999; Morrison et al., 2005).

M-PACE

Observations


Radiative influence on glaciation time scale2
Radiative Influence on Glaciation Time-Scale Mixed-Phase Clouds

Cloud Top

  • LW Cooling andSW Heating using spheres: Results similar to those for plates.

Spheres

Initial LWC: 0.1 g m-3

Ni = 1 L-1


ad