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The "Bag Breakup" Spume Droplet Generation Mechanism at High Winds. Part II: Contribution to Momentum and Enthalpy Transfer
被引:32
|作者:
Troitskaya, Yu.
[1
,2
]
Druzhinin, O.
[1
]
Kozlov, D.
[1
]
Zilitinkevich, S.
[3
,4
]
机构:
[1] Inst Appl Phys, Nizhnii Novgorod, Russia
[2] AM Obukhov Inst Atmospher Phys, Moscow, Russia
[3] Finnish Meteorol Inst, Helsinki, Finland
[4] Univ Helsinki, Inst Atmospher & Earth Syst Res, Helsinki, Finland
基金:
俄罗斯科学基金会;
芬兰科学院;
俄罗斯基础研究基金会;
关键词:
Wind stress;
Atmosphere-ocean interaction;
Hurricanes;
typhoons;
Heat budgets;
fluxes;
Surface fluxes;
Parameterization;
AIR-SEA MOMENTUM;
DRAG COEFFICIENT;
SPRAY;
HURRICANE;
EXCHANGE;
SURFACE;
IMPACT;
MODEL;
SPEEDS;
OCEAN;
D O I:
10.1175/JPO-D-17-0105.1
中图分类号:
P7 [海洋学];
学科分类号:
0707 ;
摘要:
In Part I of this study, we used high-speed video to identify bag breakup fragmentation as the dominant mechanism by which spume droplets are generated at gale-force and hurricane wind speeds. We also constructed a spray generation function (SGF) for the bag-breakup mechanism. The distinctive feature of this new SGF is the presence of giant (1000 m) droplets, which may significantly intensify the exchange between the atmosphere and the ocean. In this paper, Part II, we estimate the contribution of the bag-breakup mechanism to the momentum and enthalpy fluxes, which are known to strongly affect the development and maintenance of hurricanes. We consider three contributions to the spray-mediated aerodynamic drag: 1) bags as obstacles before fragmentation, 2) acceleration of droplets by the wind in the course of their production, and 3) stable stratification of the marine atmospheric boundary layer due to levitating droplets. Taking into account all of these contributions indicates a peaking dependence of the aerodynamic drag coefficient on the wind speed, which confirms the results of field and laboratory measurements. The contribution of the spray-mediated flux to the ocean-to-atmosphere moist enthalpy is also estimated using the concept of reentrant spray, and the equation for the enthalpy flux from a single droplet to the atmosphere is derived from microphysical equations. Our estimates show that a noticeable increase in the enthalpy exchange coefficient at winds exceeding 30-35 m s(-1) is due to the enhancement of the exchange processes caused by the presence of giant droplets originating from bag-breakup fragmentation.
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页码:2189 / 2207
页数:19
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