Short Course Challenges in Understanding Cloud
and Precipitation Processes and Their Impact on Weather and Climate
Darrel Baumgardner PhD.
Droplet Measurement Technologies [email protected]
February 18-22 3:30-4:30 pm
break 4:45-5:30 pm
Second Class
1.0 Overview of Clouds and Precipitation 1.1 Clouds and Climate 1.2 Clouds and the Hydrological Cycle 1.3 Some Issues Related to Cloud and Precipitation Physics 2.0 Microphysical Properties of Clouds and Precipitation
2.1 Bulk properties 2.1.1 Number, area and mass concentrations 2.1.2 Scattering, absorption and extinction coefficients, optical depth,
effective diameter –wavelength dependent 2.1.3 Chemical composition (inorganic and organic ions, elemental
carbon, bioaerosols 2.1.4 Electrical fields
2.2 Size dependent properties (Size distributions) 2.2.1 Mass, density and morphology 2.2.2 Optical cross section and phase function as function of
wavelength. 2.2.3 Area – surface and projected 2.2.4 Fall velocity 2.2.5 Electric charge
Some Outstanding Problems in Cloud Microphysics
I. Warm Clouds a) Stratiform
i) Drizzle formation ii) Geoengineering
b) Cumulus i) Spectra broadening ii) Rain formation
II. Cold Clouds a) Ice formation processes
i) Homogeneous and heterogeneous nucleation ii) Ice multiplication
b) Cirrus and Contrails i) Impact on climate ii) Cirrus evolving from contrails iii) Lightning generation
III. All Clouds a) Aerosol/Cloud Interactions
b) Inadvertent weather modification – do anthropogenic emissions increase or decrease precipitation?
Some Outstanding Problems in Cloud Microphysics
I. Warm Clouds a) Stratiform
i) Drizzle formation ii) Geoengineering
b) Cumulus i) Spectra broadening ii) Rain formation
II. Cold Clouds a) Ice formation processes
i) Homogeneous and heterogeneous nucleation ii) Ice multiplication
b) Cirrus and Contrails i) Impact on climate ii) Cirrus evolving from contrails iii) Lightning generation
III. All Clouds a) Aerosol/Cloud Interactions
b) Inadvertent weather modification – do anthropogenic emissions increase or decrease precipitation?
Simple Condensational Growth Model Observations
Condensational Growth rate 1/D2
Simple Condensational Growth Model Observations
Broader observed spectra lead to much faster coalescence because of the difference in terminal velocities. Models predict rain in clouds with warm tops in > 60 minutes. Rain is observed in warm clouds in < 30 minutes.
Some Outstanding Problems in Cloud Microphysics
I. Warm Clouds a) Stratiform
i) Drizzle formation ii) Geoengineering
b) Cumulus i) Spectra broadening ii) Rain formation
II. Cold Clouds a) Ice formation processes
i) Homogeneous and heterogeneous nucleation ii) Ice multiplication
b) Cirrus and Contrails i) Impact on climate ii) Cirrus evolving from contrails iii) Lightning generation
III. All Clouds a) Aerosol/Cloud Interactions
b) Inadvertent weather modification – do anthropogenic emissions increase or decrease precipitation?
Ice Multiplication processes were hypothesized when many more ice crystals were measured than predicted from simple ice nucleation versus temperature relations. Gulteppe et al., “ICE CRYSTAL NUMBER CONCENTRATION VERSUS TEMPERATURE FOR CLIMATE STUDIES, INTERNATIONAL JOURNAL OF CLIMATOLOGY, Int. J. Climatol. 21: 1281–1302 (2001)
Collisions between ice crystals producing secondary fragments
Secondary Ice Production
Q1: Hallet Mossop process more explanation is requested, in general and also if IN play a role ? Q2:Any measurements made for aerosol processing by clouds ? how ? Q3: How about the shape of ice crystals in clouds and how it impacts the radiative forcing, how it is differentiated only of contrail for eg. ? Q4: Contrail forcing at night was maximum as it is only LW forcing (SW forcing is zero ?) or because more ice crystals form ? Q5: temperature range from ice crystals to droplets ? and vice versa ?
Hallett-Mossop Secondary Ice Production
Initially, coalescence produces small supercooled raindrops (300-500 µm) which freeze then collide with droplets, forming coating of rime (supercooled droplets freezing on ice surface). When this piece of graupel, up to 1-2 mm wide, hits larger droplets they may eject ice shards. These ice shards grow into needles or columns by vapour deposition to form precipitation, and possibly also more ice-particle-generating graupel. Ice production only occurs at between -3°C and -8°C and in the presence of both large (>24 µm) and small droplets.
Very little known about this mechanism forproducing ice crystals.
‘Hallett-Mossop’ and droplet splintering are theonly processes that have been replicated in thelaboratory
Hallett-Mossop Secondary Ice Production
Secondary Ice Production Artifact?
Some Outstanding Problems in Cloud Microphysics
I. Warm Clouds a) Stratiform
i) Drizzle formation ii) Geoengineering
b) Cumulus i) Spectra broadening ii) Rain formation
II. Cold Clouds a) Ice formation processes
i) Homogeneous and heterogeneous nucleation ii) Ice multiplication
b) Cirrus and Contrails i) Impact on climate ii) Cirrus evolving from contrails
III. All Clouds a) Aerosol/Cloud Interactions
b) Inadvertent weather modification – do anthropogenic emissions increase or decrease precipitation?
Issues
• Aviation impacts on climate: radiative forcing due to
• CO2 emissions ~ 0.03 Wm-2
• Contrail-induced cirrus ~ 0.03 Wm-2 IPCC(2007)
• Indirect radiative impacts of aviation • contrail formation, persistence and growth
• modification of natural cirrus properties via impacts of emitted aerosols
Heymsfield et al (2010), BAMS: Contrail Microphysics
• Well-established theory of contrail formation • Range of existing microphysical obs. but with sub-optimal
instrumentation (prone to shattering artefacts) • Lack of recent studies of aerosol emission characteristics for
current- and future-generation engines • Difficulty of measurement in key regions to fully-characterize
the evolution of a contrail (plume-mixing region, vortex region)
• Need for lab and field obs. of soot IN activity – fresh and aged • Need for large-scale “closure” experiments to link contrails
sources, vapour availability, microphysical characteristics and radiative impact
Yang et al. (2010) BAMS: Contrails and Induced Cirrus: Optics and Radiation
• Ice habit of cirrus and contrails: when are they similar or different?
• Single-scattering properties of contrail ice.
• Possible need for separate parametrization in GCMs if optical properties are significantly different
• Ambiguity of identifying contrail cirrus when evolved beyond the linear stage
• Need for satellite climatologies of contrail cirrus
• Need for supporting field campaigns
Haywood et al. (2009): A case study of the radiative forcing of persistent contrails evolving into
contrail-induced cirrus, J.Geophys.Res.
• AWACS aircraft flying large circles off the east coast of England
• Contrail drift simulated using the Met Office NAME atmospheric dispersion model: Lagrangian particles transported by dynamical fields from operational Unified Model forecast.
• IR satellite images from sequence of polar-orbiters (NOAA 15/17/18, Metop-A, TERRA)
10:06 1006UTC ~ T+1hr
Model
10:40 1040UTC ~ T+1.5hr
11:30 1130UTC ~ T+2.5hr
12:02
Just touching coast near the Humber
1202UTC ~ T+3hr
13:42 1342UTC ~ T+4.5hr
15:26 1526UTC ~ T+6.5hr
17:08
Contribution from other contrails
1708UTC ~ T+8hr
How much of this cloud cover would have been present if the airmass hadn’t been seeded by contrails?
Spangenberg, D. A., P. Minnis, S. T. Bedka, R. Palikonda, D. P. Duda and F. G. Rose (2013), Contrail radiative forcing over the Northern Hemisphere from 2006 Aqua MODIS data, Geophys. Res. Lett., 40, doi:10.1002/grl.50168. Largest forcing is at night
Some Outstanding Problems in Cloud Microphysics
I. Warm Clouds a) Stratiform
i) Drizzle formation ii) Geoengineering
b) Cumulus i) Spectra broadening ii) Rain formation
II. Cold Clouds a) Ice formation processes
i) Homogeneous and heterogeneous nucleation ii) Ice multiplication
b) Cirrus and Contrails i) Impact on climate ii) Cirrus evolving from contrails
III. All Clouds a) Aerosol/Cloud Interactions
b) Inadvertent weather modification – do anthropogenic emissions increase or decrease precipitation?
Aerosol processing by clouds
No change in the aerosol properties
Before During After
Aerosol particles are removed or transformed when a CCN forms a droplet that then collects a non-activated particle (inertial scavenging). When the droplet evaporates, the new aerosol particle has larger mass and diameter, and possibly a new composition
Before During After
Aerosol particles are removed when two CCN form droplets that collide and coalesce and form a larger droplet. When this droplet evaporates, the new, residual aerosol particle has larger mass and diameter, and possibly a new composition
Before During After
Aerosol particles are removed when droplets collide and coalesce, form a rain drop that precipitates. This raindrop can remove other aerosol particles by inertia scavenging.
Before During After
The adsorption by droplets of some types of gases, like SO2, will also change the mass and composition of the aerosol particles.
Before During After
Cloud processing can change the morphology (shape) of the particles by adding a layer of water.
Before During After
Aerosols processed by clouds may form clouds and precipitation faster and easier!
No rain Rain
Some Outstanding Problems in Cloud Microphysics
I. Warm Clouds a) Stratiform
i) Drizzle formation ii) Geoengineering
b) Cumulus i) Spectra broadening ii) Rain formation
II. Cold Clouds a) Ice formation processes
i) Homogeneous and heterogeneous nucleation ii) Ice multiplication
b) Cirrus and Contrails i) Impact on climate ii) Cirrus evolving from contrails
III. All Clouds a) Aerosol/Cloud Interactions
b) Inadvertent weather modification – do anthropogenic emissions increase or decrease precipitation?
Why adding more CCN decreases average droplet size and increases cloud lifetime
Low concentration
of CCN
Form cloud droplets in
supersaturated environment
That grow until environment is
no longer supersaturated
Some grow to raindrops that fall
out and cloud dissipates
Why adding more CCN decreases average droplet size and increases cloud lifetime ….for clouds with low updraft and small vertical development.
High concentration of
CCN
Form cloud droplets in
supersaturated environment
That grow much slower as they
compete for available vapor
No rain forms, cloud lasts longer
Formation of precipitation: natural cloud condensation and ice nuclei
Growing Mature Dissipating
Growing Mature Dissipating
The number of cloud droplets activated under polluted conditions is not less necessarily than pristine clouds – they just take longer to activate and hence form higher in clouds and change the dynamics and rate of precipitation formation.
What are the Physics Behind Cloud Formation
And Evolution to Precipitation?
This diagram summarizes the possible pathways to the formation of precipitation. A microphysical model must take each of these pathways into account. Each arrow belongs to a process requiring individual numerical treatment/subroutine for the model simulation Figure courtesy of S.
Borrmann, U. Mainz
Hail
Aggregates
Snow Pellet
Rain Drop
Drizzle Drop
Droplet
Growth Evaporation
Evaporation Coalescence
Serves as nuclei for heterogeneous nucleation
Aerosol Particle
Serves as nuclei for ice .
Water vapor Sublimation Deposition
Condensation Evaporation
Break-up
Freezing
Melting
Freezing
Ice Xtal
Serves as aggregate embryo
Serves as aggregate embryo
Serves as aggregate embryo
Serves as hail embryo
Riming
Graupel growth
Melting
Temperature