Deep Convective Clouds over the Northern Pacific and Their Relationship with Oceanic Cyclones

Based on combined CloudSat/CALIPSO detections, the seasonal occurrence of deep convective clouds （DCCs） over the midlatitude North Pacific （NP） and cyclonic activity in winter were compared. In winter, DCCs are more frequent over the central NP, from approximately 30~N to 45~N, than over other regions. The high frequencies are roughly equal to those occurring in this region in summer. Most of these DCCs have cloud tops above a 12 km altitude, and the highest top is approximately 15 km. These wintertime marine DCCs commonly occur during surface circulation conditions of low pressure, high temperature, strong meridional wind, and high relative humidity. Further, the maximum probability of DCCs, according to the high correlation coefficient, was found in the region 10^-20~ east and 5^-10~ south of the center of the cyclones. The potential relationship between DCCs and cyclones regarding their relative locations and circulation conditions was also identified by a case study. Deep clouds were generated in the warm conveyor belt by strong updrafts from baroclinic flows. The updrafts intensified when latent heat was released during the adjustment of the cyclone circulation current. This indicates that the dynamics of cyclones are the primary energy source for DCCs over the NP in winter.

Using Satellite Data to Analyze the Initiation and Evolution of Deep Convective Clouds

In this study, two deep convective cloud cases were analyzed in detail to study their initiation and evolution. In both cases, all deep convective clouds were positioned at the rear of the cold front cloud bands and propagated backward. Satellite data showed that prior to initiation of the deep convective clouds, thermodynamic and moist conditions were favorable for their formation. In the morning, a deep convective cloud at the rear of cold front cloud band propagated backward, the outflow boundary of which created favorable conditions for initiation. An additional deep convective cloud cluster moved in from the west and interacted with the outflow boundary to develop a mesoscale convective system(MCS) with large, ellipse-shaped deep convective clouds that brought strong rainfall. The initiation and evolution of these clouds are shown clearly in satellite data and provide significant information for nowcasting and short-term forecasting.

An Algorithm to Detect Tropical Deep Convective Clouds Through AMSU-B Water Vapor Channels

An algorithm to detect tropical deep convective clouds and deep convective overshootings based on the measurements from the three water vapor channels （1833GHz± 1GHz, 183.3GHz±3GHz and 183.3GHz±7GHz） of the Advanced Microwave Sounding Unit-B （AMSU-B） is presented. This algorithm is an improved version of the method of Hong et al. （2005）. The proposed procedure is based on the statistical analysis of seven years＇ （2001-2007） measurements from AMSU-B on NOAA-16. From the 1-d histograms of the brightness temperature of the three water vapor channels and the 2-d histograms of the brightness temperature dif- ference between these channels, new thresholds for brightness temperature differences and the brigb.tness temperature of chamM 18 （183.3 GHz 4-1 GHz） are suggested. The new algorithm is employed to investigate the mean distribution of tropical deep convective clouds and convective overshootings from 30＇S to 30＇N for the years 2001 to 2007. The major concentration of deep convective clouds and convective overshootings is found over the Intertropical Convergence Zone （ITCZ）, the South Pacific Convergence Zone （SPCZ）, tropical Africa, South America, the Indian Ocean and Indonesia ruth an average fraction of 0.4%. In terms of these clouds we identity, the secondary Intertropical Convergence Zone located in the eastern South Pacific and parallel to the main ITCZ in the North Pacific. The convective overshooting is more frequently observed over land than over the ocean.

The behavior of deep convective clouds over the warm pool and connection to the Walker circulation

As the deep convective clouds(DCCs) over the western Pacific and Indian Ocean warm pool may play different roles in the climate system, variations in DCC properties over these two sectors are investigated and compared. The DCC intensity and area varies more significantly in the Indian Ocean than the western Pacific sector, while the DCC frequency is comparable in both sectors at the seasonal scale. Although the Indian Ocean sector is strongly dominated by the seasonal evolution, the interannual variations in the two sectors are comparable for all three DCC properties(frequency, intensity, and area). Besides,Walker circulation is closely correlated with the interannual variability of DCCs in both sectors. The Walker circulation strengthens(weakens) as the DCCs shift eastward(westward) over the Indian Ocean sector and westward(eastward) over the western Pacific sector. When more or stronger DCCs occur over the Indian Ocean sector(western Pacific sector), the Walker circulation becomes stronger(weaker) and shifts westward(eastward). Interestingly, the response of the Walker circulation to DCC variability over the warm pool is asymmetry. The asymmetry response of the Walker circulation to the negative and positive DCC anomaly may be related to the non-linearity internal variability of the atmosphere. DCCs over the Indian Ocean sector have a much weaker nonlinear correlation with the Walker circulation than DCCs over the western Pacific sector.