AOSC 620
Cloud & Precipitation (Rogers and Yau Chapt. 5)
Russell Dickerson 2015
Three states of water
• Water vapor
• Liquid water
• Ice crystals
A cloud is comprised
of tiny water droplets
and/or ice crystals.
A snowflake is an aggregate
of many ice crystals.
A rain drop is just liquid water.
Copyright © 2013 R. R. Dickerson
& Z.Q. Li
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http://scim.ag/aad1386_mov1
Thermal vent in Iceland
2
• Beals et al., Science, 2015.
• Airborne (underwing) in-line digital
holographic imaging system (Spuler &
Fugal, Appl. Optics, 2011)
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& Z.Q. Li
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& Z.Q. Li
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& Z.Q. Li
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Supplementary Figures
Figure S1: Holodec mounted on the (a) NCAR C-130 (upper right instrument) and (b)
University of Wyoming King Air (instrument on right) during the IDEAS 2011 and 2012
projects, respectively.
Beals et al., (2015)
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Fig. 1 Relative constancy of cloud droplet diameter during entrainment and mixing and its
possible bias from sampling and averaging.
Matthew J. Beals et al. Science 2015;350:87-90
Published by AAAS
Fig. 2 Centimeter-scale measurements of cloud droplet spatial distributions and
corresponding size distributions obtained with the HOLODEC instrument.
Matthew J. Beals et al. Science 2015;350:87-90
Published by AAAS
Fig. 3 Mean cubic droplet diameter versus cloud droplet number density n, measured with
digital holography in two convective clouds.
Matthew J. Beals et al. Science 2015;350:87-90
Published by AAAS
Final Draft (7 June 2013)
Chapter 7
IPCC WGI Fifth Assessment Report
Executive Summary
Clouds and aerosols continue to contribute the largest uncertainty to estimates and interpretations of the
Earth’s changing energy budget. This chapter focuses on process understanding and considers observations,
theory and models to assess how clouds and aerosols contribute and respond to climate change. The
following conclusions are drawn.
10
Cloud Views
~535pm LST
~1135pm LST
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& Z.Q. Li
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Cloud Optical Thickness
(The MODIS cloud products: Algorithms and examples from Terra
Platnick S, King MD, Ackerman SA, et al., IEEE TRANSACTIONS ON
GEOSCIENCE AND REMOTE SENSING, 2003.)
Level-3 Monthly
April 2001
tc
20
16
12
8
4
0
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& Z.Q. Li
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Cloud Effective Droplet Radius
(The MODIS cloud products: Algorithms and examples from Terra
Platnick S, King MD, Ackerman SA, et al., IEEE TRANSACTIONS ON
GEOSCIENCELevel-3
ANDMonthly
REMOTE SENSING, 2003)
April 2001
re(µm)
40
34
~20 mm
28
16
~10mm
10
4
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& Z.Q. Li
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0
1.0
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Cloud & Atmospheric Dynamics Interaction
Cloud Physics
Atmospheric Dynamics
Cloud condensation
Vertical motion,
convection, mixing
Cloud pattern &
structure
Stability,
convergence, fronts
and cyclones
Latent heat release, Water
vapor distribution
Radiative heating/cooling
Atmospheric
stability, general
circulation
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& Z.Q. Li
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Final Draft (7 June 2013)
Chapter 7
IPCC WGI Fifth Assessment Report
Figures
Figure 7.1: Overview of forcing and feedback pathways involving greenhouse gases, aerosols and clouds. Forcing
agents are in the green and dark blue boxes, with forcing mechanisms indicated by the straight green and dark blue
arrows. The forcing is modified by rapid adjustments whose pathways are independent of changes in the globally
averaged surface temperature and are denoted by brown dashed arrows. Feedback loops, which are ultimately rooted in
changes ensuing from changes in the surface temperature, are represented by curving arrows (blue denotes cloud
feedbacks; green denotes aerosol feedbacks; and orange denotes other feedback loops such as those involving the lapse
rate, water vapour and surface albedo). The final temperature response depends on the effective radiative forcing (ERF)
that is felt by the system, i.e., after accounting for rapid adjustments, and the feedbacks.
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& Z.Q. Li
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Basic Facts about Clouds (from ISCCP)
• On global and annual
average, cloud covers about
67.8% of the earth and varies
~1-3%
• Mean cloud top pressure
~583 hPa with a variance ~
10-40 hPa
• Mean cloud top temperature
261.5K with a variance ~ 14K
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& Z.Q. Li
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Cloud Classification
Basic Types: stratus, cumulus, cirrus, nimbus
Classification by height
Classification by morphology
• High-level clouds
>20,000 ft or 6,000 m
• Mid-level clouds
6,500 – 20,000 ft
2,000 – 6000m
• Low-level Clouds
<6,500ft or 2,000m
• High-Level Clouds
cirrus and cirrostratus.
• Mid-Level Clouds
altocumulus, altostratus.
• Low-Level Clouds
cumulus, nimbostratus and
stratocumulus
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Stratocumulus
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Radiative Impact of Different
Cloud Types
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& Z.Q. Li
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Global Climatology of High and Low
Clouds and Their Climatic Effects
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& Z.Q. Li
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Cloud Formation Mechanisms
• Lifting of thermals due to solar heating
• Lifting due to atmospheric convergence
• Lifting due to frontal system
• Radiative cooling
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& Z.Q. Li
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Lifting due to surface heating
• Condensation due to rising
of thermals or air bubbles
caused by solar heating of
the surface.
• Characteristcs:
Even surface/uneven top;
bright on side from certain
angle and darken bottom
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& Z.Q. Li
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Lifting by Convergence
• Broad lifting of an entire
layer of air
• Convergence is an
atmospheric condition that
exists when there is a
horizontal net inflow of air
into a region. When air
converges along the
earth's surface, it is forced
to rise since it cannot go
downward.
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Frontal Lifting
•
Warm Front Warm air rides along
the front (up and over the cold air
mass), cooling as it rises, producing
clouds and precipitation ahead of
the surface warm front, producing
wide spread and light rain.
• Cold Front the colder air lifts
the warmer air ahead that
condenses to produce clouds
and precipitation that are
typically more vigorous and
producing deeper clouds and
more intense bands of showers
and thunderstorms. However,
these bands are typically quite
narrow and move rapidly just
ahead of the cold front.
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& Z.Q. Li
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Influence of updraft
Influence of entrainment
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& Z.Q. Li
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& Z.Q. Li
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Vertical variations
of cloud droplet
sizes and liquid
water density for
low-level stratiform
clouds compiled
from various in-situ
measurements.
Note the general
linear increasing
trends!
Copyright © 2013 R. R. Dickerson
& Z.Q. Li
After Miles et al. (JAS, 2000 JAN)
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Vertical variations of
cloud droplet number
concentration. Note
the difference
between continental
and marine clouds.
Marine clouds have
much smaller # of
droplets which does
not change much
with height. The
opposite is the case
for continental
clouds. Why?
Copyright © 2013 R. R. Dickerson
& Z.Q.
LiMiles et al. (JAS, 2000 JAN)
After
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Particle size distribution models:
Lognormal function:
n( D ) 
N
2 D

  ln( D / Dm ) 2
exp 
2
2 log
lo g




Modified Gamma Function
 gam1
N  D 
ngam ( D ) 
( gam )  Dgam 
D
1
exp 

Dgam
 Dgam 
N: Total partical concentration
 log Logarithmic width of the
distribution
Dm: Median diameter
 gam The shape parameter
Dgam: Scaling factor Copyright © 2013 R. R. Dickerson
& Z.Q. Li
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Copyright © 2013 R. R. Dickerson
& Z.Q. Li
King et al., JAOT, 2004.
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An Investigation of Cirrus Cloud
Properties Using Airborne Lidar Data
John Yorks
Advisors:
Russell Dickerson (Academic)
Matthew McGill (Research)
PhD Dissertation Defense: 03 Apr. 2014
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Motivation: In Situ
MID-LATITUDE
TROPICAL
• Mix of rosettes (45%) and
• Anvils dominated by
irregular plates (45%)
irregular plates (75%), some
• Low extinction and IWC
columns (10%), very few
• High concentrations of small
rosettes
ice particles
• High extinction and IWC
• Higher concentrations of
large particles compared to
mid-latitudes
Cloud Type
Convective Turrets
Fresh Anvils
Aged Anvils
Mid-Latitude Cirrus
Concentration Extinction
(Number per L)
(km-1)
11100
1540
114
846
60.00
11.00
1.24
0.46
IWC
(g m-3)
1.650
0.320
0.036
0.005
Lawson et al. (2006, 2008, 2010)
PhD Dissertation Defense: 03 Apr. 2014
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Case Study: Tropical
Coincident in situ data from SPEC instruments on Learjet :
• Anvil Cirrus Observed:
– High percentage of columns
– Causes high depolarization
observed in CPL data
– Few rosettes, many irregular
plates
– High concentrations, IWC,
extinction
Cloud Type
Anvil
Concentration Extinction
(# per L)
(km-1)
397
1.652
IWC
(g m-3)
0.044
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& Z.Q. Li
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How well can we measure Cloud Water Content?
Instrumentation on NCAR C-130 during AIRS-2 project.
Rogers, D.C., J. Hallett, A. Schanot, C. Twohy, J. Jensen, J. Stith,
Copyright © 2013 R. R. Dickerson
and G. Vidaurre, 2006:
12th Conf. Cloud Physics, AMS, Madison
& Z.Q. Li
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Cloud Water Content Instruments
Hot-wire type devices
PMS King, Nevzorov, DRI large and small T-probes
These measure the current required to maintain
a wire at a const temp.
Optical probes
Scattering probes (FSSP-100),
Optical array probes (PMS 2D-C (cloud), 2D-P precp), 260-X),
HVPS (High Volume Precipitation Spectrometer),
Cloud Particle Imaging probe (CPI),
Counter-flow virtual impactor (CVI).
Uses a counter flow of N2 for size selection, evaporates the particles and
measures the humidity. Solid and liquid water measured.
http://www.eol.ucar.edu/instrumentation/aircraft/
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(Fast) forward scattering spectrometer probe – (F)FSSP
Particle Measuring Systems, Boulder, CO.
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FSSP Schematic Diagram
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FSSP spectra in a thin cloud.
Number, surface area and volume as a
function of radius in mm.
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& Z.Q. Li
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2D Cloud and Precipitation Probe
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& Z.Q. Li
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2D Cloud and Precipitation Probe
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Observations as function of time on an ascent through a
mixed-phase cloud over NE New York on 3 November 2003.
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& Z.Q. Li
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(a) Schematic representation of mixed-phase cloud showing a few ice crystals
surrounded by supercooled liquid droplets. Ice crystals grow at expense of the water
droplets, leading to depletion of the liquid water content of the cloud. (b) Individual
mixed-phase particles from laboratory observations; from left to right: freezing
droplet, melting plate and melting dendrite. T probe measurements ideally lead to an
indication of mixed-phase in all cases. Vidaurre and Hallet (2009)
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Conclusions
Cirrus warm the Earth’s surface.
Low-level cumulus cool the Earth’s surface.
Deep Cumulus ~neutral.
Supercooled water existed at temperatures as low as -22°C.
There is correlation among the hydrometeor instruments, but
offsets.
Different cloud properties are best measured by different
instruments.
Variations in density limit accuracy of ice and snow.
How do we calibrate radar?
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& Z.Q. Li
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HIAPER: The next generation NSF/NCAR research aircraft, Laursen KK, Jorgensen
DP, Brasseur GP, et al. BAMS, 87(7) 896, 2006.
Miles, N. L., J. Verlinde, and E. E. Clothiaux, Cloud droplet size distributions in lowlevel stratiform clouds, J. Atmos. Sci., 57, 295-311, 2000.
Chang, F.-L., and Z. Li, 2005, A near-global climatology of single-layer and
Copyright © 2013 R. R. Dickerson
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overlapped clouds and their optical
properties
retrieved
from
Terra/MODIS
& Z.Q. Li
Indirect Effect
Haywood and Boucher Revs. Geophys. (accepted) 2000
1) Increased CCN - reduces reff
2) Drizzle suppression - increases LWC
‘First’ indirect
effect
3) Increased cloud height
4) Increased cloud lifetime
t ~
3 LWP
2 reff
‘Second’ indirect effect
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& Z.Q. Li
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Cloud Optical Depth, t, (unitless)
LWP (cm)
Reff (cm)
t ~
3LWP
2 reff
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& Z.Q. Li
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More readings about cloud on
Internet
Cloud photos
• http://www.australiasevereweather.com/technique
s/moreadv/class.htm
Cloud type definitions
• http://vortex.plymouth.edu/clouds.html
Cloud Climatology
• http://isccp.giss.nasa.gov
NCAR Instruments
• http://www.eol.ucar.edu/raf/Bulletins/
Copyright © 2013 R. R. Dickerson
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& Z.Q. Li