[Eoas-seminar] March 4 seminar announcement for Dr. Kosuke Ito, Kyoto Univ.

[eoas-seminar at lists.fsu.edu]

Colleagues,

At 3pm on March 4 (this upcoming Tuesday) in Room 1044 there will be a seminar by Dr. Kosuke Ito, Professor at DPRI, Kyoto University, Japan.  Refreshments will be available starting at 245pm.

There will be a lunch for interested students in Room 3067 at noon on the same day, with Prof. Ito.

The seminar information is below.  His equally interesting earlier work included the modeling the ratio of drag to enthalpy coefficients in tropical cyclones, a topic critical to both understanding and forecasting tropical cyclone intensity change and peak intensity.

Bob

Title:   Three dimensional (tropical cyclone) Fujiwhara effect

Abstract:
It has been widely believed that binary tropical cyclones (TCs) rotate cyclonically and get closer to each other with respect to the center of the circulations (known as "Fujiwhara effect"). In fact, binary TCs (initially separated by 1000 km or more) move away from each other in the quiescent environment on an f-plane, based on an idealized simulation with a three-dimensional model. To investigate this phenomena, we calculated the potential vorticity (PV) budget and found that the horizontal advection term was largely compensated by the asymmetric diabatic heating. The asymmetric diabatic heating served to resist the cyclonic rotation and help the motion moving away from each other. This asymmetric diabatic heating was associated with the vertical wind shear (VWS) consisting of the upper-level anticyclonic circulation and lower-level cyclonic circulation, both of which were originally from the binary TCs. These three-dimensional Fujiwhara effects were verified in the western North Pacific using the best track and ERA5 reanalysis data. The TC motion was found to deviate systematically from the steering flow. The direction of deviation is clockwise and repelling with respect to the midpoint of the binary TCs with a separation distance of more than 1000 km. The large-scale upper-level anticyclonic and lower-level cyclonic circulations serve as the VWS for each TC in a manner consistent with the idealized simulations. The VWS of a TC tends to be directed to the rear-left quadrant from the direction of the counterpart TC, where the maxima of rainfall and diabatic heating are observed. The PV budget analysis supports that the actual TC motion is modulated by the diabatic heating asymmetry that offsets the counterclockwise and approaching motion owing to horizontal advection when the separation distance of the binary TCs is 1000–2000 km. With a small separation distance (<1000 km), horizontal advection becomes significant, but the impact of diabatic heating asymmetry is not negligible. These features are robust, while there are some dependencies on the TC intensities, size, circulation, duration, and geographical location. This research sheds light on the motion of binary TCs that has not been previously explained by a two-dimensional barotropic framework.
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