5:15 PM - 6:45 PM
[AAS06-P04] Sensitivity study of the size-intensity relationship of the tropical cyclone
Keywords:tropical cyclone, TC fullness, size-intensity relationship, sensitivity study
Size and intensity are the major factors of tropical cyclones (TCs). It is important both scientifically and socially to understand the relationship between the two characteristics. However, the complex interaction between the inner and outer core makes understanding the size-intensity relationship difficult.
Previous studies proposed analysis methods using the TC fullness (TCF), which describes the ratio of the smallness of the inner core size to the outer core size of the TC, to quantify the size configuration of TCs, considering the inner and outer core in an integrated manner. To evaluate TCF, the radius of maximum wind (RMW) and the radius of gale-force wind (R17) are used as the inner and outer core size, respectively.
In this study, the size-intensity relationship of TCs is investigated using the TCF based on sensitivity simulations. We also examine other factors explaining the size-intensity relationship and the intensification rate.
The numerical simulations were conducted using a simplified version of the Nonhydrostatic Icosahedral Atmospheric Model (hereinafter Plane NICAM). Plane NICAM runs on an f-plane with hexagonal periodicity, and previous studies have shown that it can reproduce the entire life cycle of TCs.
We used a 8-km horizontal grid spacing and 74 vertical levels up to 40 km. The model was initialized with an axisymmetric cyclone vortex. The vortex had a maximum azimuthal wind speed of 25 m/s at the surface. The wind speed is linearly decreased to zero at an altitude of 16 km. Three R17 series (200, 500 and 700 km) are conducted. For each series, RMW is ranged at intervals of 20 km.
Figure 1 shows the entire result of the numerical simulations. Solid gray lines show the time evolution of TCs. Dotted lines show the contour of TCF. Blue and red dots show the point of the maximum intensity and the high intensification rate (>1 m/s/2h), respectively. TCs tend to intensify rapidly and then reach the maximum intensity when TCF is about 0.8. We found that there were branches in the TC time evolution where the R17 increased and decreased in the phase toward the maximum intensity, and they depended on the values of R17 in the initial conditions.
Figure 2 shows the relationship between the maximum intensity and R17 at that time. The maximum intensity is likely to be small if its initial R17 is 700 km.
These results support previous studies using reanalysis datasets. It also implies that not only the TCF but the initial R17 need to be considered with regard to the relationship between size and maximum intensity.
Previous studies proposed analysis methods using the TC fullness (TCF), which describes the ratio of the smallness of the inner core size to the outer core size of the TC, to quantify the size configuration of TCs, considering the inner and outer core in an integrated manner. To evaluate TCF, the radius of maximum wind (RMW) and the radius of gale-force wind (R17) are used as the inner and outer core size, respectively.
In this study, the size-intensity relationship of TCs is investigated using the TCF based on sensitivity simulations. We also examine other factors explaining the size-intensity relationship and the intensification rate.
The numerical simulations were conducted using a simplified version of the Nonhydrostatic Icosahedral Atmospheric Model (hereinafter Plane NICAM). Plane NICAM runs on an f-plane with hexagonal periodicity, and previous studies have shown that it can reproduce the entire life cycle of TCs.
We used a 8-km horizontal grid spacing and 74 vertical levels up to 40 km. The model was initialized with an axisymmetric cyclone vortex. The vortex had a maximum azimuthal wind speed of 25 m/s at the surface. The wind speed is linearly decreased to zero at an altitude of 16 km. Three R17 series (200, 500 and 700 km) are conducted. For each series, RMW is ranged at intervals of 20 km.
Figure 1 shows the entire result of the numerical simulations. Solid gray lines show the time evolution of TCs. Dotted lines show the contour of TCF. Blue and red dots show the point of the maximum intensity and the high intensification rate (>1 m/s/2h), respectively. TCs tend to intensify rapidly and then reach the maximum intensity when TCF is about 0.8. We found that there were branches in the TC time evolution where the R17 increased and decreased in the phase toward the maximum intensity, and they depended on the values of R17 in the initial conditions.
Figure 2 shows the relationship between the maximum intensity and R17 at that time. The maximum intensity is likely to be small if its initial R17 is 700 km.
These results support previous studies using reanalysis datasets. It also implies that not only the TCF but the initial R17 need to be considered with regard to the relationship between size and maximum intensity.