Gravity-wave momentum fluxes induced by multiple convective cells

Convectively forced gravity waves (CGWs) play important roles in the atmosphere. CGW drag parameterizations for use in large-scale models typically represent subgrid-scale convection as a single convective source. This study uses an analytic framework to investigate how horizontal organization of multiple convective cells modifies the vertical flux of horizontal momentum. It is shown that the per-cell momentum flux induced by multiple convective cells is expressed as the momentum flux induced by a single convective cell times [1 +  J _n ( β , δ )]. Here, J _n ( β , δ ) is the nonlinear modification factor arising from mutual interactions among distinct convective cells, where β is the ratio of compensating-cooling width to heating-core width, δ is the nondimensional spacing between the horizontal centers of convective cells, and n is the number of cells. Closely packed deep convective cells with broad cooling (large β and small δ ) act to enhance the per-cell momentum flux relative to a single convective cell, whereas more widely spaced convective cells act to reduce it. As the number of convective cells increases, the region of positive J _n ​ in the parameter space of β and δ shrinks toward smaller δ . These results indicate that purely geometric properties of convective organization ( β , δ , and n ) systematically modify CGW momentum flux. The proposed nonlinear modification factor can be easily incorporated into existing CGW drag parameterizations.