476
K.B. Katsaros
potential vorticity anomalies during the incipient and deepening phases (e.g. Uccellini et al.,
1985, Davis and Emanuel, 1991; Reed et al., 1992; Kuo et al., 1992; Reed et al., 1993 and
Neiman and Shapiro, 1993).
Condensational Heating or Latent Heat Release
Several case studies have pointed to the presence of convection and extensive cloud shields associated with such storms (e.g. Reed and Albright, 1986; Neiman and Shapiro, 1993). Modeling
studies have shown that moist processes must be accurately included to successfully simulate
the deepening rate of the surface low, with deepening rates reduced from 30 to 70% when condensational heating is removed (e.g. Reed et al., 1993 and see further references in McMurdie
and Katsaros, 1996). The details of how latent heat contributes to cyclone deepening has only
been explored using model-derived fields (Kuo et al., 1991). The quantitative observational
evidence of the role of moist processes is lacking.
Unfortunately, since these storms most frequently occur over oceanic regions, adequate in situ
observations are unavailable. This has led forecasters and researchers to turn to remotely based
platforms to observe rapid cyclogenesis. Forecasters often rely on infrared and visible satellite
imagery to track their movement and rapid development. With the availability of remote
sensing technology, other satellite indicators of rapid development are being sought. Satellite
derived ozone maps and the 6.7 !-lm upper level moisture images gave evidence of strong upper
tropospheric subsidence in two cases of rapid development (Uccellini et al., 1985 and Reed
and Albright, 1986). Upper tropospheric thermal anomalies identified using the Microwave
Sounding Unit (MSU) were shown to be greater in storms that deepened rapidly compared to
those that did not (Velden ,1972).
With the integrated water vapor and precipitation information available from passive microwave radiometers such as the Special Sensor Microwave/Imager (SSM/I), it is now possible
to document the quantitative observational evidence of the role of latent heat release in rapid cyclogenesis. Using rain rates derived from the brightness temperatures observed by the
SSM/I, Petty and Miller (1995) found that average rain rates within a small region northeast of
the surface low was strongly correlated with the rate of deepening pressure. With information
derived from the earlier passive microwave instrument, the Scanning Multichannel Microwave
Radiometer, McMurdie and Katsaros (1985) and Katsaros et al. (1987 and 1988) showed that
the mesoscale structure in the integrated water vapor and rain distribution patterns are highly
correlated with the location of the surface frontal zones. McMurdie and Katsaros (1996) searched for indicators of rapid development in the SSM/I derived water vapor and precipitation
fields by analyzing storms that occurred in January through March 1988 and January and February 1989. The difference between ordinary and rapidly deepening storms is illustrated by
Figure 17.6.
McMurdie and Katsaros (1996) found that the integrated water amount was too variable as a
function of latitude to be a useful diagnostic parameter. However, the water vapor anomaly
(WVA) with respect to the amounts typical for the season and latitude had predictive value
over a 6 hours period. They also examined the correlation between rapid deepening and rain
rate indicated by (I-P37) or (I-PI9). P19 being less sensitive to precipitation and therefore less
likely to saturate gave a slightly better correlation. This result is seen in Figure 17.7, which is
representative of the resullts for the other predictors (WVA and I-P37) as well.
K.B. Katsaros
potential vorticity anomalies during the incipient and deepening phases (e.g. Uccellini et al.,
1985, Davis and Emanuel, 1991; Reed et al., 1992; Kuo et al., 1992; Reed et al., 1993 and
Neiman and Shapiro, 1993).
Condensational Heating or Latent Heat Release
Several case studies have pointed to the presence of convection and extensive cloud shields associated with such storms (e.g. Reed and Albright, 1986; Neiman and Shapiro, 1993). Modeling
studies have shown that moist processes must be accurately included to successfully simulate
the deepening rate of the surface low, with deepening rates reduced from 30 to 70% when condensational heating is removed (e.g. Reed et al., 1993 and see further references in McMurdie
and Katsaros, 1996). The details of how latent heat contributes to cyclone deepening has only
been explored using model-derived fields (Kuo et al., 1991). The quantitative observational
evidence of the role of moist processes is lacking.
Unfortunately, since these storms most frequently occur over oceanic regions, adequate in situ
observations are unavailable. This has led forecasters and researchers to turn to remotely based
platforms to observe rapid cyclogenesis. Forecasters often rely on infrared and visible satellite
imagery to track their movement and rapid development. With the availability of remote
sensing technology, other satellite indicators of rapid development are being sought. Satellite
derived ozone maps and the 6.7 !-lm upper level moisture images gave evidence of strong upper
tropospheric subsidence in two cases of rapid development (Uccellini et al., 1985 and Reed
and Albright, 1986). Upper tropospheric thermal anomalies identified using the Microwave
Sounding Unit (MSU) were shown to be greater in storms that deepened rapidly compared to
those that did not (Velden ,1972).
With the integrated water vapor and precipitation information available from passive microwave radiometers such as the Special Sensor Microwave/Imager (SSM/I), it is now possible
to document the quantitative observational evidence of the role of latent heat release in rapid cyclogenesis. Using rain rates derived from the brightness temperatures observed by the
SSM/I, Petty and Miller (1995) found that average rain rates within a small region northeast of
the surface low was strongly correlated with the rate of deepening pressure. With information
derived from the earlier passive microwave instrument, the Scanning Multichannel Microwave
Radiometer, McMurdie and Katsaros (1985) and Katsaros et al. (1987 and 1988) showed that
the mesoscale structure in the integrated water vapor and rain distribution patterns are highly
correlated with the location of the surface frontal zones. McMurdie and Katsaros (1996) searched for indicators of rapid development in the SSM/I derived water vapor and precipitation
fields by analyzing storms that occurred in January through March 1988 and January and February 1989. The difference between ordinary and rapidly deepening storms is illustrated by
Figure 17.6.
McMurdie and Katsaros (1996) found that the integrated water amount was too variable as a
function of latitude to be a useful diagnostic parameter. However, the water vapor anomaly
(WVA) with respect to the amounts typical for the season and latitude had predictive value
over a 6 hours period. They also examined the correlation between rapid deepening and rain
rate indicated by (I-P37) or (I-PI9). P19 being less sensitive to precipitation and therefore less
likely to saturate gave a slightly better correlation. This result is seen in Figure 17.7, which is
representative of the resullts for the other predictors (WVA and I-P37) as well.