PHYS Clouds spring ‘04 S. Platnick (NASA GSFC/UMBC PHYS Adjunct Faculty) Texts: Rogers, R.R., and M. K. Yau, A Short Course in Cloud Physics, Pergamon Press, Twomey, S., Atmospheric Aerosols, Elsevier Publishing, PHYS Clouds, spring ‘04, lect. 1, Platnick

Clouds - The “Wet” Aerosol “Wet” aerosol: much of the mathematics (e.g., size distribution, etc.) used for characterizing aerosol microphysics applies to clouds. A cloud definition: visible suspension of water and/or ice particles in the atmosphere. –Key word is visible, but not quantitative. Example, “sub-visual cirrus” (observed through non-visible, non-passive sensors/imagers or lidars). Cloud physics: branch of physical meteorology, study of cloud formation (macrophysical & microphysical), lifecycles, precipitation, radiation, etc. –Macrophysical: larger scale spatial information, total/column water amounts, etc. –Microphysical: thermodynamic phase, size distribution, ice particle shape (habit), water content, etc. PHYS Clouds, spring ‘04, lect. 1, Platnick

Why Clouds? Weather –Dynamics: Latent heat and/or radiative effects impacting atmospheric stability/instability, atmospheric heating/cooling –Radiation (e.g., surface heating) Chemical processes Climate –General circulation –Hydrological cycle –Radiation budget  Clouds are a critical component of climate models (for reasons cited above) and therefore also to climate change studies Not well-represented in climate models Climate change: cloud-climate feedback, cloud-aerosol interactions (to be discussed), etc. PHYS Clouds, spring ‘04, lect. 1, Platnick

1. Evaporation, transpiration (plants) 2. Atmospheric transport (vapor) 3. Condensation (liquid water, ice) 4. Precipitation 5. Surface transport (continental rivers, aquifers and ocean currents) Earth’s Hydrological Cycle - Schematic PHYS Clouds, spring ‘04, lect. 1, Platnick

NASA TRMM (Tropical Rainfall Measurement Mission) Tropical cyclone Elita Precipitation Radar PHYS Clouds, spring ‘04, lect. 1, Platnick

TRMM 16 Feb 2004 weekly global rainfall accumulation PHYS Clouds, spring ‘04, lect. 1, Platnick

Earth’s Radiation Budget - Schematic

CERES (Clouds & Earth Radiant Energy System experiment) Radiation Budget Measurements - NASA Terra (March May 2001) PHYS Clouds, spring ‘04, lect. 1, Platnick Record setting heat wave in CA, NV Courtesy CERES Science Team, NASA LaRC

PHYS Clouds, spring ‘04, lect. 1, Platnick Cloud-aerosol interactions ex.: ship tracks (27 Jan. 2003, N. Atlantic) MODIS (MODerate resolution Imaging Spectroradiometer)

Cold front - steep frontal slopes Warm front - shallow frontal slopes Convective development (mesoscale, local) Synoptic development PHYS Clouds, spring ‘04, lect. 1, Platnick

MODIS (MODerate resolution Imaging Spectroradiometer) true-color composite, NASA Terra, ~1030 LT PHYS Clouds, spring ‘04, lect. 1, Platnick

Cloud Classifications (a nomenclature) PHYS Clouds, spring ‘04, lect. 1, Platnick Genera (main groups - high, middle, low altitude clouds, and clouds of vertical extent) Species (shape, structure) Variety (special characteristics) Cirrusuncinus, fibratus, … CirrocumulusStratiformis, lenticularis Cirrostratusfibratus Altocumulus Altostratus high level mid-level

Cloud Classifications, cont. PHYS Clouds, spring ‘04, lect. 1, Platnick GeneraCommon SpeciesVariety Nimbostratus Stratocumulus Stratus Cumulushumilus, congestus Cumulonimbus low level (base) vertical extent (potentially)

cirrus alto cumulus cirrostratus: thin cirrus, note 22° halo => hexagonal crystals, parhelia (sundogs) => oriented crystals PHYS Clouds, spring ‘04, lect. 1, Platnick

cumulus (fair weather) mammatus (implies sinking air) PHYS Clouds, spring ‘04, lect. 1, Platnick cumulus congestus (from NASA WB-57, July )

PHYS Clouds, spring ‘04, lect. 1, Platnick Kelvin-Helmholtz waves

Cumulonimbus (from NASA ER-2, July ) PHYS Clouds, spring ‘04, lect. 1, Platnick

Overview of Cloud Climatologies (statistics) - What do we know? How do we know it? PHYS Clouds, spring ‘04, lect. 1, Platnick Quantities of interest –Cloud frequency (fraction), cloud-top height, cloud phase (ice vs. liquid water), optical properties (optical thickness), microphysics (particle size), column water amount (aka, “water path”), solar and IR radiative impact Historic data sets –Ground observations e.g.: Warren, S. G., et al. 1988: Global distribution of total cloud over and cloud type amounts over the ocean. NCAR/TN-317+STR [Available from the National Center for Atmospheric Research, Boulder, CO, 80307] –Satellite observations ISCCP (International Satellite Cloud Climatology Project), solar reflective & IR techniques –amount, temperature, optical thickness, water path HIRS (High Resolution Infrared Radiation Sounder - on NOAA polar orbiters), GOES VAS (VISSR [Vis-Ir Spin-Scan Sounder] Atmospheric Sounder) –amount, effective emissivity, and pressure heights with “CO2 slicing” technique

Overview of Cloud Climatologies (statistics), cont. PHYS Clouds, spring ‘04, lect. 1, Platnick SSM/I () - microwave passive remote sensing –liquid water path ERBE (Earth Radiation Budget Experiment) - mid-80’s, instruments flown on the Earth Radiation Budget Satellite (ERBS), and NOAA -9, -10 Recent/new data sets –Satellite observations Solar IR imager: MODIS, flown on Terra, Aqua Microwave: AMSR (Japanese ADEOS-II), AMSR-E (Aqua) Radiation Budget: CERES (Clouds and the Earth’s Radiant Energy System) - next generation of radiation budget measurements, flown on TRMM, Terra, Aqua

HIRS cloud frequency vs. month [Wylie et al., Journal of Climate, Vol. 7, No. 12, December, 1994]

HIRS cloud frequency vs. altitude (September)

HIRS cloud frequency vs. month for “thicker” clouds (opt thickness >6)

ISCCP climatology examples low-level cloud amount (%)

ISCCP climatology examples mid-level cloud amount (%)

ISCCP climatology examples high-level cloud amount (%)

AMSR-E cloud liquid water path Sept 2003 (from F. Wentz, PHYS Clouds, spring ‘04, lect. 1, Platnick

Cloud Microphysics PHYS Clouds, spring ‘04, lect. 1, Platnick

Clouds Particle Scales

Cloud Microphysical Quantities Size distribution [n(r)] - droplet size pdf Thermodynamic phase (liquid water, ice) Number concentration [N] - e.g., cm -3 ; range: 10’s cm ’s cm -3 for liquid water droplets, 10 liter -1 for ice particles Water Content [LWC, IWC] - mass density, e.g., g-m -3 Water Path [W] - vertical integration of water content, e.g., g-m -2 Particle Size Moments –Mean –Effective radius [r e ] - radiatively relevant moment PHYS Clouds, spring ‘04, lect. 1, Platnick

Cloud Microphysical Quantities schematic of vertically inhomogeneous cloud (horizontally homogeneous) surface

MODIS monthly cloud fraction - Sept Ice cloud fraction Liquid water cloud fraction Sc regimes ITCZ (climatological feature) PHYS Clouds, spring ‘04, lect. 1, Platnick

MODIS monthly cloud particle size retrievals - Sept Ice cloud particle effective radius Liquid water cloud particle effective radius (QA) Sc regimes PHYS Clouds, spring ‘04, lect. 1, Platnick

Clouds are difficult, in part, by the nature of the relevant spatial scales and interdisciplinary fields ScaleRelevant Physics synoptic ~1000s km (large scale dynamics/thermodynamics, vapor fields) mesoscale~100s km local (cloud scale) <1-10 km (dynamics/thermodynamics, turbulence, mixing) particle µm - mm (nucleation, surface effects, coagulation, turbulence, stat-mech) molecular

PHYS Clouds, spring ‘04, lect. 1, Platnick Cold Cloud Processes Warm Cloud Processes

PHYS 622 Clouds Emphasis on cloud microphysics: cloud particle nucleation, growth Water Clouds –Formation concepts –Water path for adiabatic cloud parcel –Nucleation theory for water droplets Ice Clouds Precipitation mechanisms PHYS Clouds, spring ‘04, lect. 1, Platnick Next 2,3 lectures }