Binary Tropical Cyclone During Their Mutual Rotation And Its Response To Environmental Moisture Transport

Tropical cyclones (TCs), especially super typhoons, are one of the most powerful natural phenomena, which may bring torrential precipitation, dangerous storm surge, flash flooding, and disastrous winds to the impacted areas. Thus, it is of great interests to accurately predict tracks, intensities, and the abrupt intensity changes of TCs in operational forecasts. Apparently, tropical cyclone intensity change interweaves multi-scale nonlinear interactions among different physical processes and weather systems. Such interactions include environmental moisture transportation and binary TC (BTC) interaction.(1) Super Typhoon Saomai (2006,08W), which hit in the southern China in August2006, is the most powerful typhoon ever making landfall in the Mainland China since1949and caused historical disaster in the region. The relationship of impact by Tropical Storm Bopha (2006,10W) on Saomai is regarded as a binary tropicalcyclone interaction, which means two typhoons interact each other. We used a mesoscale numerical model to quantify the influence of Bopha on the intensities of Saomai. Sensitivity experiments are performed by artificially modifying the circulation of Bopha with different intensities. It is shown that changing Bopha intensities has significant effects on Saomai’s intensities, structures and tracks through the Connecting Body Channel (CBC), which links the circulations of Bopha and Saomai. The CBCs are the key bridge in the binary tropical cyclone interaction process. It is interesting that existence of Bopha and increase of its intensity tends to produce stronger transportation from Saomai to Bopha through CBCs, more asymmetrical structures and further northward tracks of Saomai. However, our further analysis indicates the opposite effects by Bopha are shown at different development stage of Saomai. The existence of Bopha and increase of its intensity would weaken Saomai at its intensifying stage while intensify at its weakening stage. A possible explanation of the effects of Bopha on the different development stage of Saomaiis the direction change of moisture transportation from/toSaomai at its intensifying/weakening stages through CBCs.It may suggest a significant relevance for operational intensity forecasts in such a case under active binary tropical cyclone interaction.(2) we explored a possible mechanism responsible for the exceptional rainfall overTaiwan by Typhoon Morakot by the means of the investigation of the binary typhoon vortices (BTV) interaction. The analysis of the three-dimensional thermal-dynamic structure revealed that there is substantial moisture, energy transport from the typhoon Goni to Morakot. The inherent correlation between two vortex development and decay is also obvious, indicating occurrence of mutually rotation. The dynamic vertical structure of two vortexes presents an opposite tendency, namely, the intensity of typhoon Goni vortex becomes weaker and asymmetric with the time elapsed, in contrast to the continuous development of "Morakot" during the period of the BTV interaction. However, the horizontal structure of energy and potential vortices distribution of two vortexes is characterized by obvious’connecting body’transportation. Significantmoisture transport channel from typhoon ’Goni’ to ’Morakot’ can be deduced from the further analysis on the correlation between the satellite blackbody temperature (TBB) over Taiwan areas and the moisture column flux around its surrounding areas. Using the trajectories model FLEXPART coupling with a mesoscale weather forecasting mode WRF, we reproduced this moisture transport pathway by the backward tracking of majority of air parcels initialized over the cores of Goni. In addition, numerical simulation experiment with ’Goni’ vortex being removed or not further confirmed thatthemoisture and energy transportation from ’Goni’ is one of the key factors for the development and maintenance of typhoon ’Morakot’. Generalized the above data diagnosis, trajectory analysis and numerical simulation, the three-dimensional image of BTV interaction is provided to describe the energy, moisture transport of BTV, and development, decay of BTV.(3) BTV Lionrock and Namtheum get closer during their mutual rotation. In the process of their mutualrotation, they attracted to each other. In the strong water vapor from the southwest airflow, first to form the "Lionrock" to the Namtheum Connect Body Channel (CBC), then the north also appear CBC from Namtheum to Lionrock which can transport energy and water vapor along it direction. Thus the south and north CBC is unified to one ring shaped structure, at last binary tropical cyclones Lionrock and Namtheum tend to merge. Diagnostic analysis shows that, during merging process the tropical cyclone Lionrock and Namtheum, Namtheum’s structure is destroyed, and the rainbandsof Namtheum became part of Lionrock. Sensitivity experiment shows that typhoon Compasu have little impact on merge of Lionrock and Namtheum. However, typhoon Compasu interacted with Lionrock after merging of Lionrock and Namtheum completed. Of interesting is that Taiwan topography play an important role in the merging of two TC. Absence of Taiwan topography, Namtheum intensified, but Lionrock weakened. So the process of merging role of two TC switched.