Open AccessFlow Regimes of Nonlinear Heat Island Circulation
Author(s) -
Hiroshi Niino,
Atsushi Mori,
Takehiko Satomura,
Sayaka Akiba
Publication year - 2006
Publication title -
journal of the atmospheric sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.853
H-Index - 173
eISSN - 1520-0469
pISSN - 0022-4928
DOI - 10.1175/jas3700.1
Subject(s) - prandtl number , mechanics , flow (mathematics) , thermal diffusivity , nonlinear system , circulation (fluid dynamics) , boundary layer , thermodynamics , physics , anomaly (physics) , thermal , heat transfer , condensed matter physics , quantum mechanics
Previous laboratory and numerical experiments show that the nonlinear heat island circulation has two different flow regimes: One has two maximums of updraft at both edges of the heat island (type E), while the other has a single maximum of updraft at the center of the island (type C). Our theoretical consideration shows that the heat island circulation is principally governed by two nondimensional parameters: a nonlinear parameter ɛN = Δθ/(Γδ) and a Prandtl number Pr = ν/κ, where Δθ is the surface temperature anomaly of the heat island, Γ the vertical gradient of the basic potential temperature, δ the thickness of the thermal boundary layer, ν the kinematic viscosity, and κ the temperature diffusivity. For a given fluid, the Prandtl number is fixed, so that the flow regime is principally determined by the nonlinear parameter ɛN. Numerical experiments are performed to confirm the theoretical prediction. The steady-state flows obtained from the numerical experiments are categorized into either of the two regimes. In accordance with the theoretical prediction, the transition between the two regimes occurs at a critical value of ɛN(∼3.4). When ɛN is larger (smaller) than this critical value, type C (type E) is realized. The physical mechanism for the transition is interpreted in the light of the authors' previous theoretical study.