The effect of atmospheric diabatic heating on low-frequency oscillations

Yen, Ming-Cheng
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A diagnostic scheme is devised to illustrate a chain relationship between diabatic heating and planetary-scale divergent and rotational circulations. The scheme consists of the velocity-potential ([chi]) maintenance equation, which relates diabatic heating and velocity potential, and the streamfunction ([psi]) budget equation, which depicts the streamfunction tendency caused by the imbalance between streamfunction tendencies induced by vorticity advection and source. The proposed scheme is employed to examine the effect of tropical diabatic heating on the annual variation of subtropical jet streams. Furthermore, the [chi]-maintenance analysis is used to examine how the 30-60 day oscillation of planetary-scale divergent circulation is maintained; and the [psi]-budget analysis is performed to illustrate how the 30-60 day velocity potential (~[chi]) mode interacts with the upper-level monsoon flow to induce the 30-60 day oscillation of the tropical easterly jet;It was found that annual variations of both tropical diabatic heating and planetary-scale divergent circulation exhibit an annual in-phase seesaw oscillation between the winter and summer hemispheres. The annual variation of subtropical jet streams is caused by the adjustment of atmospheric rotational flow through planetary-scale divergent circulation in response to the annual cycle of tropical diabatic heating;The [chi]-maintenance equation is expressed as [chi] = [chi][subscript]sp Q. - [chi][subscript] HA, where [chi][subscript]sp Q. and [chi][subscript] HA are the effects of vertical differential diabatic and adiabatic heating, respectively. The 30-60 day [chi] oscillation is shown to be primarily maintained by the differential diabatic heating effect, which can be inferred from the H[subscript] VD anomalies, the Laplician of the filtered [chi][subscript]sp Q. anomalies. The resemblance of the H[subscript] VD and OLR anomalies in terms of the geographic distributions indicates that the differential diabatic heating effect maintaining the 30-60 day [chi] oscillation is attributable to the latent heat released by cumulus convection;The synoptic relationship among (~[chi], ∇~[chi]) (200 mb), OLR and ~[psi] (200 mb) makes clear the synchronization of the 30-60 day oscillation of the tropical easterly jet and the Somali jet. The significant outcome of the [psi]-budget analysis demonstrates that the 30-60 day oscillation of the southern part of the tropical easterly jet is a response of the upper-level monsoon circulation to the eastward propagating ~[chi] mode.

Geological and atmospheric sciences, Meteorology