A1260947665AEutX

1
Investigating Properties of the West African
Monsoon Using the QuikSCAT and Tropical Rainfall
Measuring Mission (TRMM) Satellites April 23,
2008 Taylor Hays Katie Yoder Mary Moore
2
Effect of the Intraseasonal Wind Fluctuations in
the West African Monsoon on Air-Sea
Fluxes Study conducted by Semyon Grodsky and
James Carton 2001
3
Background
The West African Monsoon occurs during the
Northern Hemisphere summer and is strongest from
mid-May until October
During this time, the intensity of the monsoon
fluctuates, with periods of heavy rain as well as
dry, sunny days
4
Background
Two well-documented wave-like functions are
present during monsoon

• African Waves
• Zonal Wavelength 2500-3000 km
• Period 3-5 days
• Westward movement 9-10 m/s

2. Second Type (unnamed) Zonal Wavelength gt6000
km Period 6-9 days Westward movement 11 m/s
5
Goals of This Research Project
Grodsky and Carton wanted to investigate a
possible 3rd wave-function
Bi-weekly Oscillation Occurs near the equator by
the ITCZ around April-June and does not appear to
propagate westward To conduct this study,
wind data from QuikSCAT and rainfall estimates
from Tropical Rainfall Measuring Mission (TRMM)
were analyzed
6
QuikSCAT
7
Overview

• Provides wind speed and direction information
  over oceans to NOAA
• Purpose is to fill in the gap created by the loss
  of data from the NASA Scatterometer that was lost
  in June 1997.
• Launched June 19, 1999

8
Specs

• Circles Earth at an altitude of 800km
• Orbits once every 101 minutes (14 orbits per day)
• Passes close to Earths north and south poles
• Inclination of 98.6º
• Seawinds is the Scatterometer instrument onboard

9
SeaWinds

• Microwave radar that measures near-surface wind
  speed and direction
• Rotating dish antenna with two spot beams that
  sweep in a circular pattern
• Radiates microwave pulses at a frequency of 13.4
  gigahertz across broad regions on Earth's surface
• Collects data over ocean, land, and ice
• Continuous 1,800 km wide band
• Approximately 400,000 measurements
• Covers about 90 of Earth's surface in one day
• QuikSCAT is currently the only US-owned
  instrument in orbit that measures surface winds
  over the oceans

10
Image from SeaWInds of a tropical storm
11
Objectives

• Acquire all-weather, high-resolution measurements
  of near-surface winds over global oceans.
• Determine atmospheric forcing, ocean response,
  and air-sea interaction mechanisms on various
  spatial and temporal scales.
• Combine wind data with measurements from
  scientific instruments in other disciplines to
  help us better understand the mechanisms of
  global climate change and weather patterns.
• Study both annual and semi-annual rain forest
  vegetation changes.
• Study daily/seasonal sea ice edge movement and
  Arctic/Antarctic ice pack changes
• Improve weather forecasts near coastlines by
  using wind data in numerical weather- and
  wave-prediction models.
• Improve storm warning and monitoring.

12

• Ascending Pass

13

• Descending Pass

14
QuikSCAT Storm Page

• The storm centered imagery are generated based on
  storm center files provided by NRL(Naval Research
  Laboratory at Monterey).
• These files are updated whenever new information
  about active storms become available
• Since QuikSCAT 1800 km wide swath on the results
  in twice per day coverage over a given geographic
  region.
• Display the current and past wind vector images
  for the selected storm.
• Brighter means higher backscattered power levels,
  which in ocean scenes generally implies increased
  small scale (2-5cm) roughness on the surface.

http//manati.orbit.nesdis.noaa.gov/cgi-bin/qscat_
ice.pl
15
QuikSCAT Ocean
QuikSCAT is a polar orbiting satellite with an
1800 km wide measurement swath on the earth's
surface. Generally, this results in twice per day
coverage over a given geographic region.
This page contains the most recent wind vector
images covering the Atlantic Ocean, Indian Ocean,
East Pacific and West Pacific Ocean. It is
updated shortly after reciept of new QuikSCAT
orbit data files.
EPAC qscat ATL qscat
                                                                   
http//manati.orbit.nesdis.noaa.gov/cgi-bin/qscat_
ocean.pl
16
QuikSCAT Ice Page

• The daily ice image products are generated from
  SeaWinds
• This page contains the most recent images
  covering the Antarctic, the Arctic, the Ross Ice
  Shelf, South Georgia Island and the Weddell Sea.
• The Antarctic and Arctic products typically span
  a 24-hour data period, while the other regions
  span a 38-hour period.

http//manati.orbit.nesdis.noaa.gov/cgi-bin/qscat_
ice.pl
17
Bad News

• The instruments still work, but the satellite
  that carries it has begun to show signs of age.
  Some of the sensors that provide orientation have
  failed and its transmitter is wearing out.
• Because it is now running on a backup transmitter
  and having other problems, this satellite has the
  potential could fail at any moment, jeopardizing
  weather forecasts for potentially dangerous
  tropical storms.
• In early June 2007, Bill Proenza, Director of the
  National Hurricane Center in Florida, came under
  fire for criticizing his NOAA superiors for not
  pursuing a back-up plan for replacing the
  capabilities provided by this satellite.

18
Tropical Rainfall Measuring Mission (TRMM)
19
Overview

• Joint mission between NASA and JAXA
• Studies/Moniters tropical rainfall
• Launched Nov 27, 1997
• First mission dedicated to measuring rainfall

20
Specs

• Circular orbit at altitude of 350km
• 35 degree inclination
• 91 minute orbit (16 orbits per day)
• Great coverage of tropics of 24 hour period
• Land and sea measurements

21
Spatial Coverage
22
Payload

• Precipitation Radar (PR)
• TRMM Microwave Imager (TMI)
• Visible Infrared Scanner (VIRS)
• Clouds and the Earths Radiant Energy System
  (CERES)
• Lightning Imaging Sensor (LIS)

23
Precipitation Radar (PR)

• Swath width 250km
• Ground resolution 5km
• Phased array antenna
• Vertical profiles of rain/snow

24
(No Transcript)
25
TRMM Microwave Imager (TMI)

• Swath width 880km
• 5 frequencies 10.7, 19.4, 21.3, 37, 85.5 GHz
• Uses Plancks Radiation Law to calculate rainfall
  rates

26
Visible Infrared Scanner (VIRS)

• Swath width 830km
• Picks out cloud features small as 2.4 km
• 5 spectral regions from 0.63 to 12 micrometers
• Delineates rainfall
• Used as standard to other measurements
• POES
• GOES

27
(No Transcript)
28
Good News

• Long lifetime of satellite
• Global distribution of rainfall
• Better predictions of rainfall
• Under-sampled ocean and tropical continental
  areas
• GPMM due to launch in 2013

29
Results
Found that trade winds reverse about every 2
weeks (12-15 days), which was determined by
tracking wind direction changes as well as
precipitation location changes.
Reversal may result from interactions between
Africas hydrological cycle, land heating, and
tropical trade winds
30
Results
Illustration of the wind, rainfall, and land
heating cycles that cause the bi-weekly
oscillation to develop
31
Conclusions
Grodsky and Carton were able to detect the
bi-weekly oscillation during the West African
Monsoon with the aid of the wind observations
from QuickSCAT and rainfall amounts from TRMM
32
Questions/Comments?