The goal of this study is to assess the relative importance of the two modes in the maintenance of KWs by quantifying and comparing the eddy available potential energy (EAPE) generation associated with them. The vertical structure of the two vertical modes for temperature and apparent heating is obtained empirically as the two leading EOFs using ERA5 reanalysis data. Then the EAPE production rate - the normalized covariance between temperature and apparent heating - is calculated in the wavenumber-frequency and physical domain for each vertical mode. Also examined is the extent to which the EAPE production rate is associated with various characteristics of KW precipitation such as the signal strength in the wavenumber-frequency domain, and the spatial and seasonal variation in the physical domain.

In the wavenumber-frequency domain, the second mode EAPE production rate is positive across the KW band, while the first mode EAPE production rate over the KW band is negative. The positive second mode EAPE production rates appear in the wavenumber-frequency band in which KW signal strength is pronounced. In the physical domain, the second mode EAPE production rate is positive in the tropical Indo-Pacific warm pool and Atlantic Ocean, where KWs are active. On the contrary, the first mode EAPE production rate is overall negative in the tropics. Geographically, the positive second mode EAPE production rates are collocated with high KW precipitation variance and they show consistent seasonal migration in the meridional direction. Our results are supportive of the simple models for KWs in which KWs are destabilized by the second baroclinic mode.