464
K.B. Katsaros
Midlatitude Cyclones
* In midlatitude cyclones the leading edge of frontal zones is related to strong gradients in
integrated water vapor.
* Precipitation, flagged by an index, outlines the low and the fronts.
* Waves on the cold front are seen very well in water vapor content or precipitation indices.
* Rapidly deepening cyclones compared to standard storms show statistically larger
amounts of anomalous water vapor content (anomalous with respect to the monthly mean
for that location) and precipitation near the low center in the 6-hour period preceding
the deepening.
Polar Lows
* These systems can be identified in the scattering index, and may identify such storms
before classical methods do.
* The surface wind speeds are well observed with microwave radiometers in this type of
storm, because of the low liquid water content in the clouds.
Tropical Cyclones
* The large amount of water in these storms leads to saturation of the microwave emission
based precipitation algorithm (37 GHz polarization index) over most of the storm, but
the 85 GHz scattering index gives valuable information about where the convective towers
are located.
* Microwave radiometery is almost useless for observing surface winds because of the rain
obscuring the surface, while scatterometry at C-band seems to have only weak interference
by the rain.
* The scatterometer wind fields reveal long lines of convergence in the rear of Tropical
Cyclones. These are typical features both in the southern and northern hemispheres.
* Amount of rain and organization of the rainbands as the storm develops and a convergence
of the external rain bands to form a second eye-wall during a re-intensification phase have
been noted in agreement with a suggestion by Willoughby et al. (1982).
This chapter starts with a description of the microwave instruments employed in these studies:
the Special Sensor Microwave/Imager (SSM/I) flown on Defense Meteorological Satellites since
1987, and the Active Microwave Instrument (AMI) flown on the European Remote Sensing
Satellites ERS-l and 2 since 1992. The AMI can be operated as a scatterometer, providing
surface vector winds, and in SAR (synthetic aperture radar) mode. Of special interest for this
chapter is the SAR operated in Wave Mode, which provides 5 km x 10 km SAR 'imagettes'
just inside the scatterometer swath.
After introduction of the instruments we outline the physics of radiometric measurements of the
atmospheric moisture content (column integrated water vapor, liquid water, and precipitation
size ice particles) and the surface wind speed, as well as scatterometer and SAR measurements
of surface wind vectors and sea state. Several research projects concerned with use of microwave
remote sensing to identify features in subtropical clouds and in storms are then discussed in
some detail.
K.B. Katsaros
Midlatitude Cyclones
* In midlatitude cyclones the leading edge of frontal zones is related to strong gradients in
integrated water vapor.
* Precipitation, flagged by an index, outlines the low and the fronts.
* Waves on the cold front are seen very well in water vapor content or precipitation indices.
* Rapidly deepening cyclones compared to standard storms show statistically larger
amounts of anomalous water vapor content (anomalous with respect to the monthly mean
for that location) and precipitation near the low center in the 6-hour period preceding
the deepening.
Polar Lows
* These systems can be identified in the scattering index, and may identify such storms
before classical methods do.
* The surface wind speeds are well observed with microwave radiometers in this type of
storm, because of the low liquid water content in the clouds.
Tropical Cyclones
* The large amount of water in these storms leads to saturation of the microwave emission
based precipitation algorithm (37 GHz polarization index) over most of the storm, but
the 85 GHz scattering index gives valuable information about where the convective towers
are located.
* Microwave radiometery is almost useless for observing surface winds because of the rain
obscuring the surface, while scatterometry at C-band seems to have only weak interference
by the rain.
* The scatterometer wind fields reveal long lines of convergence in the rear of Tropical
Cyclones. These are typical features both in the southern and northern hemispheres.
* Amount of rain and organization of the rainbands as the storm develops and a convergence
of the external rain bands to form a second eye-wall during a re-intensification phase have
been noted in agreement with a suggestion by Willoughby et al. (1982).
This chapter starts with a description of the microwave instruments employed in these studies:
the Special Sensor Microwave/Imager (SSM/I) flown on Defense Meteorological Satellites since
1987, and the Active Microwave Instrument (AMI) flown on the European Remote Sensing
Satellites ERS-l and 2 since 1992. The AMI can be operated as a scatterometer, providing
surface vector winds, and in SAR (synthetic aperture radar) mode. Of special interest for this
chapter is the SAR operated in Wave Mode, which provides 5 km x 10 km SAR 'imagettes'
just inside the scatterometer swath.
After introduction of the instruments we outline the physics of radiometric measurements of the
atmospheric moisture content (column integrated water vapor, liquid water, and precipitation
size ice particles) and the surface wind speed, as well as scatterometer and SAR measurements
of surface wind vectors and sea state. Several research projects concerned with use of microwave
remote sensing to identify features in subtropical clouds and in storms are then discussed in
some detail.