Time-Dependent Nonlinear Hadley Circulation

Abstract

The time-dependent Hadley circulation is studied numerically in a nonlinear, nearly inviscid, axially symmetric primitive equation model, with the heating varying periodically on an annual cycle. The annual average of the Hadley circulation strength in this model with time-dependent heating is about a factor of 2 stronger than the steady-state response to the annual mean heating and is closer to the observed strength in the real atmosphere. This is caused by the fact that heating centered off-equator tends to produce stronger meridional circulation in the winter hemisphere than in the case when the heating maximum is located at the equator, as pointed out previously by Lindzen and Hou. However, unlike the steady-state solutions, there is no abrupt change as the heating center is moved off the equator.The temperature response in this time-dependent model is simple to understand. In the tropical region, where there is a variable, but persistent, Hadley circulation, the temperature is homogenized latitudinally. In the highlatitude region, where there is no meridional circulation (in the absence of the eddies), the temperature response goes through an annual cycle with a phase lag relative to the phase of the heating. This response is as predicted by the simple time-dependent temperature equation in the absence of meridional circulation.

Biotic pump of atmospheric moisture as driver of the hydrological cycle on land

“…(17), and the scale height h H 2 O ∼2 km of the vertical distribution of atmospheric water vapor make it possible to estimate the global mean atmospheric eddy diffusion coefficient (which, for atmospheric air, coincides with the coefficient of turbulent kinematic viscosity) as ν∼w E h H 2 O ∼6 m 2 s −1 . This estimate agrees in the order of magnitude with, but is about two times greater than, the phenomenological value of ν∼3.5 m 2 s −1 used in global circulation studies (Fang and Tung, 1999).…”

“…In contrast, turbulent fluxes are caused by air eddies that are maintained by certain physical forces acting on macroscopic air volumes and making them move; thus, the eddy diffusion coefficient depends on air velocity. Therefore, using the empirically established eddy diffusion coefficient for the determination of the characteristic air velocity via the scale length of the considered problem, a common feature of many theoretical studies of global circulation, e.g., (Fang and Tung, 1999), represents a circular approach. It sheds no light on the physical nature and magnitude of the primary forces responsible for air motions.…”

Where do winds come from? A new theory on how water vapor condensation influences atmospheric pressure and dynamics

“…For example, modern global circulation models do not satisfactorily account for the water cycle of the Amazon River Basin, with the estimated moisture convergence being half the actual amounts estimated from the observed runoff values (Marengo, 2006). We note that climate science offers no quantitative theory of Hadley circulation based on current theories and the effects of differential heating alone (Held and Hou, 1980;Fang and Tung, 1999;Schneider, 2006). Efforts to address this challenge are ongoing but progress is limited (e.g., Lindzen and Hou, 1988;Robinson, 2006;Schneider, 2005, 2006).…”

Expansion of the Hadley Cell under Global Warming: Winter versus Summer

“…However, since the annual-mean state is not physically realized in the real atmosphere, it is questionable if the interpretation for the annual-mean change can be extended to each season given the nonlinear dynamics of the HC (Held and Hou 1980;Lindzen and Hou 1988;Plumb and Hou 1992;Fang and Tung 1999). For instance, the winter HC is relatively closer to the nearly inviscid limit while the summer HC is more subject to the influence of eddy momentum fluxes originating from the midlatitudes (Schneider and Bordoni 2008;Bordoni and Schneider 2010).…”