Unformatted text preview: CLOUDS AND
MSC 243 Lecture #3
9/8/11 LAB 2, Question 5 Road Map: September
Today: Homework 1 given Tuesday 13th: Lab on Satellite imagery Tuesday 13th: Homework 1 due Thursday 15th: Radar Tuesday 20th: Hurricane Lab (if there is a hurricane!) Thursday 22nd: Fronts and Forecasting Thursday 22nd: Homework 2 given Monday 26th: We start forecasting! Surface Winds
spiral into and
around a low
center http://www.rap.ucar.edu/weather/model/ Surface winds
spiral out from
around a high
center Temperature Advection
If Surface winds carry (“advect”) warmer/colder air, the local temperature will increase/decrease
Blue circle: area of cold advection
Red circle: area of warm advection http://www.rap.ucar.edu/weather/model/ This Lecture
Types of Clouds Satellites •
• Geostationary and Polar
Visible, Infrared and Water Vapor
Identifying clouds from satellites
Other types of satellite imagery Types of Clouds
Types Sorted by height • High (> 7km) Cirrus (ci), Cirrostratus (cs), Cirrocumulus (cc)
• Middle (27km) Altostratus (as), Altocumulus (ac)
• Low (< 2km) stratus (st), cumulus (cu), strato
cumulus (sc) Types of Clouds
Types Sorted by structure
• Cirrus – Composed of Ice, ‘wispy’
Cumulus – Detached elements ‘puffy’
Stratus – Uniform Layer, ‘sheetlike’
Nimbo – Precipitation producing
Nimbostratus Cumulonimbus Cirrus Clouds
Cirrus Ice crystals (frozen supercooled water droplets). Fair weather, point in direction of air movement at their elevation.
Often associated with changing weather. Cumulus Clouds
Cumulus As Earth is warmed by the sun, bubbles of warmer air (thermals) rise upward from the surface. Water vapor in a thermal cools and condenses as it rises and mixes with the surrounding air. Stratus Clouds
Stratus Uniform gray cloud that covers the entire sky. Sometimes accompanied by a light mist or drizzle. Cumulonimbus
Cumulonimbus Thunderstorm clouds, much larger and more vertically developed than fair weather cumulus. Formed by convective updrafts. Water droplets at lower levels, ice crystals at higher levels. Radiation in the Atmosphere
Radiation Effect of Clouds on Temperature
When forecasting maximum temperatures, remember that thick clouds absorb solar radiation, reducing heating at the surface. When forecasting minimum temperatures, remember that thick clouds inhibit surface cooling. Note that thin cirrus clouds have less of an effect than thick low clouds. Satellite Imagery
Satellite 1st weather satellite: TIROS 1 (1960)
Satellites observe clouds as well as nonvisible radiation (aerosols, ozone) Rest of lecture:
Interpretation of images
Other types of satellite imagery Geostationary Orbiting Satellites
Geostationary Satellite observes same area at all times. Continuous sampling. 36000km from Earth’s surface! Polar Orbiting Satellites
Polar Satellite observes globe in “swaths” 7001700km from Earth’s surface Polar Orbiting Satellites
Polar Radiative Transfer
Radiative Electromagnetic radiation: alternating electric and magnetic fields. Radiative Transfer
Radiative Radiation is specified by wavelength or frequency. Speed = freq x length microwave Radiative Transfer
Electromagnetic radiation can transport energy. Fundamental radiation unit: radiance Radiance = energy per unit time per unit wavelength per unit solid angle crossing a unit area 90o to beam. RADIOMETER measures energy per unit time striking it, at select frequencies (or wavelengths). NASA Satellite Radiometer
NASA Radiative Transfer
Radiative Each object (including us!) emits radiation with a particular frequency spectrum.
Satellite instruments are designed to measure radiances in specific frequency channels, corresponding to the desired frequency that objects / gases emit at a given temperature. Radiative Transfer
Radiative Radiative energy depends on wavelength λ and also temperature T.
One can estimate temperature from brightness: “brightness temperature”.
Total emitted radiation E = σ T4
Radiation reaching a body is then ABSORBED, REFLECTED or SCATTERED OUT by the body. Visible Image
Visible VIS imagery indicates the amount of solar radiation reflected from the Earth and clouds, in the 0.4 to 0.7 micron range. A VIS image is an approximation of the albedo (% of sunlight reflected by the Earth’s surface or clouds). Light tones show high reflectivity, darker tones show low reflectivity. Features on the surface of the Earth or in the atmosphere vary in their reflectivity and can be discerned on a VIS image. No data at night. The large, thick clouds appear white since they have a high albedo. Thinner clouds appear light to medium gray. The ocean, with a very low albedo, appears nearly black. The land, characterized by albedos that depend on the nature of the surface, appears as various shades of gray. Infrared Image
Infrared The highest (and coldest) cloud tops appear blue (or white on b/w image). Lower clouds appear as orange (lighter shades of gray), and warmer land and water surfaces appear as red (darker shades of gray). The IR sensors on board the polar orbiting and geostationary satellites measure the amount of infrared energy emitted by the Earth and the atmosphere. Because the amount of energy emitted depends on the temperature of the surface, IR imagery is essentially a picture of the surface and cloud top temperatures. This information can be used to observe thermal properties of the Earth and the atmosphere. Water Vapor Image
Water In addition to the visible and thermal infrared images, it is possible to record energy absorbed and reradiated by water vapor.
Infrared energy radiated by water vapor at wavelengths of 6.7 and 7.3 microns is measured by the satellite radiometer and converted to “brightness temperature”. The grayness of each pixel in a WV image corresponds to a specific brightness temperature. Water vapor imagery shows the altitude of the highest moist layer in the atmosphere, not just cloud patterns. Meteorologists are able to observe large
scale circulation patterns even when clouds are not present. The red (darker on b/w) regions are where very little water vapor exists in the middle and upper troposphere, and the purple/blue (lighter on b/w) regions are moist. What is this?
What VIS IR What this is
Snow Cirrus Stratus Snow Cirrus Stratus Snow is reflective, but not too cold. Stratus in Mississippi is the same, and the wispy but cold values in Ontario are cirrus
http://www.rap.ucar.edu/weather/satellite/ What is this?
What VIS IR What this is
Nimbus Cirrus Cumulus Cumulo
Nimbus Cirrus The low (warm) and scattered clouds in Georgia are cumulus. The scattered by higher clouds in central Florida are cumulonuimbus. The wispy clouds southwest of Florida are cirrus clouds What this is
MCN TPA Cumulus Cumulo
Nimbus Cirrus MCN TPA Cumulus Cumulo
Nimbus Cirrus KMCN 272053Z 28008KT 10SM FEW055 33/19 A2999 RMK AO2 SLP152 T03280194 58023=
KTPA 272053Z 01015KT 6SM TS HZ FEW020 BKN040CB BKN080 OVC250 28/23 A3005 RMK AO2
TSB45 SLP175 FRQ LTGICCG TS OHD-N MOV S TCU E VCSH VIS LWR N T02780228 56015= Other Satellite Products
Other Satellites observe at many frequencies. The most widely used frequencies are not able to ‘see’ through clouds.
Here is a collection of satellite products useful for hurricane analysis and prediction. Winds from Satellite – Upper Level
Winds Water Vapor and Infrared.
http://tropic.ssec.wisc.edu/ Winds from Satellite – Low Level
Winds Tracking the velocity of lowlevel clouds Wind Shear
Wind 200 hPa wind – 850 hPa wind Upper Level Divergence
Upper “Spreading out” of wind at upper levels. Low Level Vorticity
Low “Local spin” of atmospheric elements Saharan Air Layer
Saharan This imagery is created by differencing the 12.0 and 10.7µm infrared channels. This difference is sensitive to the presence of dry and/or dusty air in the lower atmosphere (~600850 hPa or ~4,5001,500 m) and is denoted by the yellow to red shading. This imagery is useful for monitoring the position and movement of dry air masses such as the Saharan Air Layer (SAL). Advanced Microwave Sounding Unit
Advanced Tropical Rainfall Measuring Mission
(TRMM) – Microwave Imager
(TRMM) Before eyewall replacement After eyewall replacement Sea Surface Temperature
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This note was uploaded on 01/08/2012 for the course MSC 243 taught by Professor Majumdar,s during the Fall '08 term at University of Miami.
- Fall '08