A Positive Feedback Process Related to the Rapid Development of an Extratropical Cyclone over the Kuroshio/Kuroshio Extension

• Published in: Monthly weather review 2018-02, Vol.146 (2), p.417-433
• Main Authors: Hirata, Hidetaka, Kawamura, Ryuichi, Kato, Masaya, Shinoda, Taro
• Format: Article
• Language: English
• Subjects: Ascent; Atmospheric boundary layer; Belt conveyors; Boundary layer stability; Boundary layers; Cold; Convective instability; Cyclones; Enthalpy; Experiments; Extratropical cyclones; Feedback; Frontogenesis; Heat; Heat flux; Heat transfer; Heating; Influence; Instability; Latent heat; Mixing ratio; Moisture; Moisture flux; Positive feedback; Roles; Saturation; Sensible and latent heat; Sensible heat; Stability; Updraft; Water vapor; Water vapor content; Water vapour
• ISSN: 0027-0644; 1520-0493
• DOI: 10.1175/MWR-D-17-0063.1

The active roles of sensible heat supply from the Kuroshio/Kuroshio Extension in the rapid development of an extratropical cyclone, which occurred in the middle of January 2013, were examined by using a regional cloud-resolving model. In this study, a control experiment and three sensitivity experiments without sensible and latent heat fluxes from the warm currents were conducted. When the cyclone intensified, sensible heat fluxes from these currents become prominent around the cold conveyor belt (CCB) in the control run. Comparisons among the four runs revealed that the sensible heat supply facilitates deepening of the cyclone’s central pressure, CCB development, and enhanced latent heating over the bent-back front. The sensible heat supply enhances convectively unstable conditions within the atmospheric boundary layer along the CCB. The increased convective instability is released by the forced ascent associated with frontogenesis around the bent-back front, eventually promoting updraft and resultant latent heating. Additionally, the sensible heating leads to an increase in the water vapor content of the saturated air related to the CCB through an increase in the saturation mixing ratio. This increased water vapor content reinforces the moisture flux convergence at the bent-back front, contributing to the activation of latent heating. Previous research has proposed a positive feedback process between the CCB and latent heating over the bent-back front in terms of moisture supply from warm currents. Considering the above two effects of the sensible heat supply, this study revises the positive feedback process.