Local partitioning of the overturning circulation in the tropics and the connection to the Hadley and Walker circulations

Abstract

Conceptually, it is useful to partition the three-dimensional tropical circulation into meridional and zonal components, namely, the Hadley and Walker circulations. The averaging involved in their definitions can introduce ambiguities. These problems can be circumvented by first partitioning the total vertical mass flux into components associated with overturning in the meridional and zonal directions, respectively, called here the local Hadley and local Walker circulations. Defining the local Hadley and local Walker circulations this way ensures the pair of two-dimensional overturning circulations can be added to give the original three-dimensional circulation, even when the averages are taken over limited domains. The method is applied to the vertical motion from the ERA-Interim reanalysis for the period 1979 to 2009. One important result is that the local Hadley circulation responds much more strongly to ENSO than the local Walker circulation, even though the local Walker circulation in the central Pacific weakens during El Niño years and strengthens and widens during La Niña years.

Role of dust direct radiative effect on the tropical rain belt over Middle East and North Africa: A high‐resolution AGCM study

“…This procedure is strictly defined for the global domain, and it fails for a particular longitudinal belt as mass continuity does not hold [ Trenberth et al , ; Webster , ]. Recently, Schwendike et al [] introduced a new method for the local partitioning of the tropical overturning circulation into local Hadley and Walker circulation. In this approach, the pressure velocity omega ( ) can be divided into components associated with meridional ( ω φ ) and zonal ( ω λ ) overturning circulations, as where potential function, μ , and vector stream function, Ψ , are defined in pressure coordinate as where …”

“…The divergent circulation in the plane ( U φ , ω φ ) is overlaid as vectors to show the flow direction and cell structure (Figure a). The meridional divergent wind, U φ , is estimated [ Schwendike et al , ] from the definition of horizontal divergent wind in terms of velocity stream function ( Ψ ) as …”

Enhanced biennial variability in the Pacific due to Atlantic capacitor effect

“…The PNA index44 was constructed based on the 500 hPa geopotential height anomalies. Following the method defined by Schwendike et al 45,. the Atlantic Hadley circulation index was defined as the 500 hPa vertical mass flux difference between an equatorial [5° S–5° N, 80° W–20° W] and a subtropical band [10° N–25° N, 80° W–20° W].…”

Evaluating Climate Models with an African Lens

“…One fundamental question is where and when the model is placing its peak ascent, and whether that ascent induces dry biases poleward of the locus of convection. Here, we analyze the seasonal cycle of vertical velocity, based on omega at 500 hPa (ω 500 ), a well-established measure of the large-scale vertical motion (Bony et al 2004;Oueslati and Bellon 2015), which has been used to diagnose tropical circulation in previous work (e.g., Schwendike et al 2014) and can be compared between models and reanalysis.…”