ATMS 373C.C. Hennon, UNC Asheville Observing the Tropics.

ATMS 373 C.C. Hennon, UNC Asheville

Observing the Tropics

ATMS 373 C.C. Hennon, UNC Asheville

Buoys

• Two types– Drifter

• Attached to sub-surface anchor (“drogue”) 15 meters below surface

• Drogue can measure mixed layer currents• Floats freely on water surface• Average lifespan is 400 days• Weigh between 44 and 100 lbs.• Data transmitted to passing satellites

– ARGOS

ATMS 373 C.C. Hennon, UNC Asheville

http://www.aoml.noaa.gov/phod/dac/gdp_drifter.html

Surface Float

Drogue

ATMS 373 C.C. Hennon, UNC Asheville

http://www.aoml.noaa.gov/phod/graphics/dacdata/globpop.gif

ATMS 373 C.C. Hennon, UNC Asheville

ATMS 373 C.C. Hennon, UNC Asheville

Buoys

• Two types– Moored

• Anchored to sea floor• Generally located near coastlines• Provide important information for landfalling TCs• Data collected and monitored by National Data

Buoy Center (NDBC)

ATMS 373 C.C. Hennon, UNC Asheville

Buoy regions controlled by the National Data Buoy Center

ATMS 373 C.C. Hennon, UNC Asheville

TAO Array – Detection and observation of ENSO events - Consists of 70 buoys

ATMS 373 C.C. Hennon, UNC Asheville

ATMS 373 C.C. Hennon, UNC Asheville

http://www.oc.nps.navy.mil/webmodules/ENSO/TAO.html

ATMS 373 C.C. Hennon, UNC Asheville

Hurricane Katrina Passage over moored buoy GDIL1

ATMS 373 C.C. Hennon, UNC Asheville

Katrina just 65 miles to the west (145 mph)Significant wave height = 16.9 m (55.5 ft)Maximum wave height (statistically derived)= 32.1 m (109 ft)!!

SWH = Averageof highest 1/3of waves

ATMS 373 C.C. Hennon, UNC Asheville

Reconnaissance Flights

• Aircraft penetrations of TCs

• Performed since 1944

• GPS Dropsonde most critical instrument– measures temperature, humidity, pressure,

winds– data available in near-real time at National

Hurricane Center

ATMS 373 C.C. Hennon, UNC Asheville

http://www.gsfc.nasa.gov/gsfc/earth/pictures/camex4/dropsonde.gif

ATMS 373 C.C. Hennon, UNC Asheville

“Hurricane Hunters”

• 53rd Weather Reconnaissance Squadron– Keesler AFB, Biloxi MS– 10 C-130 planes

ATMS 373 C.C. Hennon, UNC Asheville

ATMS 373 C.C. Hennon, UNC Asheville

Tropical Rainfall Measurement Mission (TRMM)

• First space-borne precipitation radar

• Measures precipitation between 35°N and 35°S

• Used for a lot of purposes– surface soil moisture– lightning research– detection of Madden-Julian Oscillation– improving SST datasets

ATMS 373 C.C. Hennon, UNC Asheville

Tropical Rainfall Measurement Mission (TRMM)

• “Active” sensors– Precipitation

Radar (PR)

• “Passive” sensors– TRMM

Microwave Imager (TMI) http://www.atmos.washington.edu/~houze/RAHouzeWebsite/houze_files/trmmsat.gif

ATMS 373 C.C. Hennon, UNC Asheville

TRMM and Tropical Cyclones

• TMI used to identify circulation centers that may be obscured in IR imagery

• PR provides information about rain rate

ATMS 373 C.C. Hennon, UNC Asheville

TRMM pass over Tropical Cyclone Manou. The inner swath (PR) shows rainfall rates (red = highest); the outer swath (TMI) detects rainbands, and can also be

used to detect circulation centers.

TMI pass near landfall of the 2004 Brazilian hurricane. Red areas represent strong convection. The center of the circulation is noted with an arrow.

ATMS 373 C.C. Hennon, UNC Asheville

QuikSCAT

• Scatterometer– Emits pulse of radiation (13.4 GhZ) toward

ocean surface– Capillary waves (1 cm) on ocean surface

backscatter pulse– More roughness = higher surface wind

speeds– Wind direction can be determined by varying

the azimuthal “look angle”• Observe same spot from at least 4 angles

ATMS 373 C.C. Hennon, UNC Asheville

900km

53 deg

803 km

46 deg

QuikSCAT Operation

ATMS 373 C.C. Hennon, UNC Asheville

ATMS 373 C.C. Hennon, UNC Asheville

Uses of QuikSCAT

• Able to retrieve high resolution (25 or 12.5 km) 10-meter wind speed and direction

• Cross swath width of 1800 km• 90% global coverage daily• Accurate within 2 m/s for wind speeds

of 2-20 m/s (~4 - 40 kt)• Data are assimilated in global weather

models and have made them more accurate

• Have helped TC forecasters identify tropical depressions and maximum extent of wind

• Identify ITCZ and other tropical wind features

ATMS 373 C.C. Hennon, UNC Asheville

TD-14 (2003). QuikSCAT resolves circulation center that is not apparentvia any other means.

ATMS 373 C.C. Hennon, UNC Asheville

Limitations of QuikSCAT

• Unrealistic wind directions for TCs and other rainy areas

• Egregious wind speed errors in rainy regions

• Areas of ocean missed in between swaths

ATMS 373 C.C. Hennon, UNC Asheville

Rain Impacts on QuikSCAT Data

• Rain contaminates the QuikSCAT data:– Attenuates beam (lowers retrieved wind

speed)– Increases backscatter of the beam (raises

retrieved wind speed)– Splash drops on surface enhance backscatter

(raises retrieved wind speed)

• What’s more important? – Depends on rain rate and true surface wind

speed

ATMS 373 C.C. Hennon, UNC AshevilleNHC Winds = 140 kt. MSLP = 932 mb

QuikSCAT surface windsHurricane Isabel (2003)

ATMS 373 C.C. Hennon, UNC Asheville

Advanced Microwave Sounding Unit (AMSU)

• Passive Radiometer• Onboard polar orbiting NOAA satellites• Senses microwave radiation• Can determine atmospheric temperatures

for many layers– 15 different channel sensors– Soundings

• Used to diagnose warm cores in TCs and TC intensity

ATMS 373 C.C. Hennon, UNC Asheville