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Unraveling the Life Cycle of Low Clouds. Mark A. Miller Rutgers University . Suppressed environments f avor low clouds Significant (but not overwhelming) subsidence Adequate BL water vapor Source of BL TKE Saturation beneath the inversion Shallow clouds dominate regardless the time of day

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unraveling the life cycle of low clouds
Unraveling the Life Cycle of Low Clouds

Mark A. Miller

Rutgers University

slide2

Suppressed environments favor low clouds

    • Significant (but not overwhelming) subsidence
    • Adequate BL water vapor
    • Source of BL TKE
    • Saturation beneath the inversion
    • Shallow clouds dominate regardless the time of day
  • Cloud Systems
    • Eastern Ocean Stratocumulus
    • Northern ocean and Arctic Stratus
    • Wintertime continental stratocumulus
    • Continental Forced Cumulus
thermodynamic profiles in stratocumulus clouds
Thermodynamic Profiles in Stratocumulus Clouds

Adiabaticity

Adiabatic

Cloud

Sub-Cloud

Nicholls, 1984

fundamental relationships
Fundamental Relationships

Shortwave Albedo

Assume extinction efficiency Qe≈2

Liquid Water Path (LWP)

How much total liquid in the cloud?

How much surface area does

the liquid have?

Effective Radius

--Mean radius for scattering

Kim et al. 2003

slide9

Optical Depth as measured by MFRSR

  • LWP Measured by Microwave Radiometer
  • Observations made every 5 mins
science questions
Science Questions
  • What are the relationships between optical depth, effective radius and liquid water path under different cloud regimes?
    • Different cloud types
    • Different stages of cloud life cycle
ship based data sets from se pacific vocals rex 2008
Ship-based data sets from SE Pacific (VOCALS-Rex 2008)
  • Radars
    • Scanning C-band
    • Vertically-pointing cloud radar
  • Scanning Doppler Lidar
  • Soundings
  • Microwave radiometer
  • Satellite imagery

NOAA ship Ronald H. Brown

It’s like MAGIC!

Courtesy of Sandra Yuter

typical open cells with intermediate drizzle
Typical open cells with intermediate drizzle

dBZ

23 Oct 2008, 12 UTC

1 deg

120 km

Max 27 dBZ

2 km

Courtesy of

Sandra Yuter

automated cell tracking 3 min data
Automated Cell Tracking (3 min data)

Projected position based on track’s

established direction and speed

Cells connected to tracks based on proximity and number of pixels of overlap with projected position

Courtesy of

Sandra Yuter

slide15

Reflectivity

 Filtered/Enhanced

 Cells Identified

“Cell” = contiguous group of pixels > 6 dBZ and  0.5 km2 (8 pixels, each 0.25 km x 0.25 km)

Cell’s centroid and area are calculated

Courtesy of

Sandra Yuter

slide17

Drizzle cell increasing in intensity

Counts

Cell’s Max dBZ change per scan

Slowly decreasing

Drizzle cell decreasing in intensity

Minutes into Track

science questions1
Science Questions
  • How does drizzle influences the cloud field and affects the life-cycle of stratocumulus clouds?
  • How does drizzle influences the formation of open/closed cells?
slide19

Xiquan’s Talk:

Focus on statistics of Azores/SGP Clouds

cumulus topped bl
Cumulus topped BL

Stevens, 2006

marine trade cumulus
Marine Trade Cumulus

General conditions associated with a fair weather boundary layer

Ghate et al., 2011

forced cumulus clouds
Forced Cumulus Clouds
  • exists only while there is forcing from the ML thermal
  • lifespan of several minutes as long as updraft is sustained
  • air entering cloud base is quickly deflected back into ML by inversion
  • no venting of ML air into free atmosphere above
    • vapor and pollutants trapped
  • thin clouds with -diameters roughly equal ML depth

Inversion Base

LCL

Parent ML Thermal

slide25

Reach Convective Temperature (T = Tc)

LFC

CIN

700

Pressure (hPa)

800

1000

0

40

20

30

10

Temperature (°C)

slide26

Reflectivity

Doppler Velocity

Ghate et al., 2011

slide27

Active

Reflectivity

Passive

Forced

Forced

Doppler Velocity

Ghate et al., 2011

science needs
Science Needs
  • Routine observations of forced clouds at the ARM sites.
  • Observations of associated liquid water path and radiation.
slide30

Bragg Scatter

Amplified

Dual

Wavelength

LWC

Stevens 1999

science needs1
Science Needs
  • More frequent measurements/retrievals of temperature and humidity in both clear and cloudy conditions.
mwrp thermodynamic profiles
MWRP Thermodynamic Profiles

Courtesy of

Lynne DiPretore

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