Heat, momentum, and mass transfer measurements in indirect ...
Lecture 6 Observational network Direct measurements (in situ= in place) Indirect measurements,...
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Transcript of Lecture 6 Observational network Direct measurements (in situ= in place) Indirect measurements,...
Lecture 6
• Observational network
• Direct measurements (in situ= in place)
• Indirect measurements, remote sensing
• Application of satellite observations to study the tropical atmosphere
ASOS (automated surface observing system)
• Cloud height• Visibility• Precipitation• Pressure• Temperature• Dew point• Wind direction and speed• Rainfall accumulation
The station model for weather obs.
Observations, data assimilation
• The “point” observations are fed into a comprehensive numerical weather prediction model that “adjusts” the observations to correct for errors, fill in gaps etc to produce gridded fields that are dynamically consistent.
• Analysis products are observations that have been “fed” through a model to check for errors, adjust for consistency etc
Direct measurements of upper-air variables
• Radiosondes are instrument packages carried aloft by helium filled balloons
• measure vertical profiles of temperature, humidity, pressure. Velocity may be inferred by tracking; in that case called rawinsonde
• Rawinsonde measurements are made at weather stations worldwide, at least twice per day
Reflection -- Refraction
Index of refraction:Speed of light inVacuum divided by speed of light in substance
Scattering
• Radiation can be absorbed, reflected or transmitted. Also, scattered = when light changes direction after interacting with a particle.
• Rayleigh scattering: when the particles are small compared to the wavelength (e.g., molecules)
• Geometric (Mie) scattering: when particles are large (e.g., drops).
Scattering (cont’ued)
• Rayleigh scattering: same amount of energy scattered both forward and backward
• Geometric scattering: more energy scattered forward
Indirect methods of observing the atmosphere
• Passive sensors: measure radiation emitted by the Earth System or by the sun
• Active sensors emit radiation into the atmosphere and then measure the returning radiation.
• How does radiation interact with the atmosphere. Reflection/refraction
Note the atm window, the visible channel (both “see” the surface), water vapor channel measures total column water vapor (sees the atm higher up)
Multiple scattering
Repeated scattering of light. Causes whitish light because light of all colors is scattered toward the eye.
Both high and low clouds in sunshine look white due to scattering.
Bottom appears grey– little light
Top appears white because of scattering
Multiple scattering and climate change
Human activities have lead to increased amount of aerosols. Lead to different clouds (smaller and more numerous droplets) increased scattering. Also, increased concentration of aerosols increases scattering.
• Cooling effect• It may be hiding some of the warming due
increased greenhouse gases
Satellite observations – GEO, LEOGeostationary Earth Orbit
Low Earth Orbit
Satellite observations
• GEO: GOES E & W series of satellites. Always above the same point over the equator. Continuous view of the tropics and midlatitudes. High latitudes not seen.
• LEO flies from pole to pole. Flies over tropics and midlatitudes twice per day.
Passive measurements (radiometers)
• Visible channel, near 0.6 micron• IR channel, in atm window 10-12 micron• Water vapor channel (6.5—6.9)
Visible detects albedo (of surface or cloud)IR detects emission temperature of object
radiating (either surface or cloud top)Wvc detects the total column of H2O (g).
Visible image
Infrared image
Visible/IR satellite images of clouds
Water vapor channel
Upper to middle troposphere
Other satellite measurements (active)
• Surface vector wind (scatterometer), example: QuikScat
• Atmospheric composition, Aura
• Surface characteristic of land, Terra
• Ocean properties, Aqua
• Rainfall, TRMM
The global satellite observation system: geostationary (35800 km), polar orbiting (850 km), R&D (orbit between certain latitudes at a few 100 km)
Satellites are the primary means of global-scale obs, grouped by orbit
Satellite based precipitation radar: Tropical Rainfall Measurement Mission (TRMM) launched in 1997. With a 250 km swath it can only observe each location once or twice per day.
Provides precip measurements where most of it falls (tropics). GEWEX
IR water vapor from GOES
Visible
Combine measurements from many satellites
POES soundings
Water vapor and cloud track winds
(each color a different satellite)
Vertical structure (soundings)
Satellite derived mid-upper level wind (track water vapor features in upper troposphere and cloud elements in lower troposphere). Limitation: height determ
Low level wind
Soundings from GPS radio occultation
Observing tropical clouds and rain
• The A train consists of a number of satellites that follow each other in succession so that they are approximately viewing the same scene at the same time
• Polar orbiters• CloudSat is the first mm wavelength cloud radar in space
– more than 1000 time more sensitive than weather radars– Collects data about the vertical structure of clouds, including
liquid water and ice and how clouds affect solar & terrestrial radiation
• Particle concentrations, cloud liquid water, precip rate
CloudSat, CALIPSO, Aqua pass almost at the same time
CloudSat profile
GOES image
3D structure
TS Ernesto
Aqua IR image
CloudSat profile (reflectivity)
Vertical structure of hurricanes from CloudSat. 3D structure by combining with OLR(Gordon)
With the radar can distinguish between cirrus and deep convection
Scatterometry from space: surface wind (2D)
QuikScat has proven incredibly useful for tropical meteorology as well as for oceanography
Satellite images of the shallow ITCZ (20 Sept 2000)
VS
IR