Pillars of excellent communication Memorable Honest Provides context Useful

Remote Sensing of the Atmosphere Types of Observations: 1. In Situ: instrument in direct contact with “object” it senses 2. Remotely sensed: instrument not in direct contact with “object” it senses -- uses radiation emitted or reflected by “object” (a) Active: emit, then collect (receive) radiation (x-ray machine) (b) Passive: receive radiation emitted or reflected by object (camera, satellite)

What is radiation ? -- Everything emits radiation (most is invisible) terrestrial radiation – emitted by earth and atmosphere -- Molecular vibration (oscillating electrons) generates radiation Wavelength (WL) Figure 2.2 Amplitude -- Shorter wavelength  more energy (waves at beach analogy)

Type of radiation emitted depends on TEMPERATURE (what is temperature Higher temperature  shorter wavelengths  higher energy Sun emits mostly visible radiation, some ultraviolet and infrared Earth/atmosphere system emits infrared wavelength

Satellite Imagery Then (1960) and now Weather satellites measure the amount of radiation reflected or emitted at certain wavelengths.

GOES: Geostationary Operational Environmental Satellite 2 types of weather satellites: Geostationary & Polar-Orbiting GOES: Geostationary Operational Environmental Satellite Geostationary: ~22,500 miles up Orbit at same speed earth rotates Ideal for “movies”

GOES-West view GOES-East view

Polar-orbiting: ~530 miles up Orbit pole to pole, image in swaths 2 types of weather satellites: Geostationary & Polar-Orbiting Polar-orbiting: ~530 miles up Orbit pole to pole, image in swaths See each point about twice / day

Resolution: How much detail can you see? Polar orbiters: highest resolution ~250 m visible Geostationary: PRE GOES-R! highest resolution ~1 km visible ~4 km infrared

Thick clouds (e.g. T’storm), high albedo  bright white 3 types of weather satellite imagery 1. Visible: uses reflected visible radiation (measures albedo) Thick clouds (e.g. T’storm), high albedo  bright white Thin clouds (e.g. cirrus, cumulus) low albedo  not as bright

2. Infrared: Uses infrared radiation emitted by clouds and earth; 2. Infrared: Uses infrared radiation emitted by clouds and earth; (warmer = more radiation emitted) The higher (colder) the cloud, the less radiation it emits Surface warmest (usually), emits most radiation Useful day and night Standard Infrared image Hottest = brightest Coldest = darkest

Bright white = cold high clouds (top of thunderstorm, ice clouds) Visible Standard infrared What meteorologists show Bright white = cold high clouds (top of thunderstorm, ice clouds) Dull white (gray) = warmer clouds closer to ground Dark = surface

“Color-enhanced” infrared

3. Water Vapor Visible Infrared Water Vapor -- Special infrared image that also “sees” invisible water vapor -- Can only detect clouds/vapor above ~10,000 feet -- When looped, traces high altitude winds Water Vapor

Weather satellites – more than just clouds … Water temperature Measure infrared energy emitted by water Convert into temperature Wave Height

GOES – R (GOES 16)

Radio Detection And Ranging Weather Radar Radio Detection And Ranging -- “Active” remote sensing -- Originally used radio waves, now microwaves -- Emitted radiation strikes “targets” (precipitation, birds, insects, buildings, mountains) -- Reflected radiation collected, analyzed, displayed. (animation)

Weather Radar History 1957 - First network of weather radars in U.S. B&W, no “looping” Used heavily in WW2 (mainly detect planes & ships) Pacific typhoon (1944) Hurricane Carla (1961)

Weather Radar History -- Current network of government radars: WSR-88D (Weather Surveillance Radar, circa 1988, with Doppler)

Each radar has range of ~250 miles

Radar- How does it work? Emits pulse (beam) of microwave radiation Portion of radiation returns to radar ECHO!!!! Detects ……. INTENSITY ….. Units of dbz Depends on … precip. density (more targets = more reflection) LOCATION ….. V = D/T Distance = VT / 2!

Radar Limitations ATTENUATION RESOLUTION RANGE INTERFERENCE Weakening of signal with distance Caused by ….. RESOLUTION RANGE Caused by …. INTERFERENCE Ground clutter “Near ground” glutter Anomalous propagation

Some Radar “issues” -- Snow reflects 5 times less radiation than rain -- Easy to underestimate intensity of snowstorms 1 hr later “Overshoot” shallow clouds at great distance

Some Radar “issues” Evaporating precipitation – Radar detects precipitation, but it evaporates before reaching ground 1 hr later

DSM Radar – what’s this?

CLE radar – what’s real?

RADAR: DERIVED FIELDS COMPOSITING ….. ANY LIMITATIONS?

Single site radar (CTP)

COMPOSITE RADAR COMPOSITING ….. Differences ?? Caused by ??

Radar: Derived fields Estimated Precipitation State College: 1.25” of rain occurred Any limitations here? Allentown: 3.25” of rain occurred

Radar: Derived fields Snow, mixed … How does it do it? We don’t call it “CrapRad” for nothing!

RADAR: Conventional VS Dual Polarization -- Dual polarization radar sends both a horizontal and vertical pulse -- By analyzing the characteristics of the two pulses additional information about the size, shape, and uniformity of the target is obtained -- This helps with target type (rain, snow, hail, debris, non-meteorological?)

Displaying Precipitation Intensity “Winter Radar” “Reflectivity” mode – shows where precip falling, and intensity Intensity proportional to amount of radiation reflected

Doppler Capability Measure winds toward and away from the radar (“Velocity Mode”) Detect rotation inside t’storms Great Doppler Velocity Tutorial T’storm View from above Radar Tornado in reflectivity mode (hook echo) Tornado in velocity mode

Train approaches, higher pitch. Train departs, lower pitch. Doppler effect: Pitch (frequency) of sound depends on motion of source Train approaches, higher pitch. Train departs, lower pitch. Applies to radiation … frequency of reflected radiation depends on whether drops are moving toward or away from radar

Is this a problem?

Is this better?

How / where / when do we take regular weather observations? Figure 1.20 Automated surface observation system (ASOS) -- every hour (or more often) -- about 1500 places in U.S. (mostly airports) Few 100 buoys (mainly just offshore)

How / where / when do we take regular weather observations? -- Temp, wind, humidity measurements above ground: radiosondes (packages of weather instrumentation) via balloon -- Twice a day (00Z and 12Z) from ~80 locations in US, few hundred more worldwide -- Increasingly supplemented by aircraft observations and from satellites