Anomalous heating distributions and the MJO in CAM4

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Description

Vertical and horizontal heating distributions are critical in determining the strength, location, and duration of the Madden-Julian Oscillation (MJO). Implementing a technique we developed to add either idealized or realistic heating distributions to CCSM4.0, we showed in our previous work that correctly simulating the horizontal distribution of tropical heating is critical for accurate modeling of the MJO. We also showed the importance of the heat and moisture exchanges that take place at the ocean-atmosphere interface. In this current work, we employ the same technique to look at tilted heating distributions, both idealized and observed. We use idealized distributions of heating that are tilted to mimic the east-west progression of shallow convective, deep convective, and stratiform clouds that is observed to pass during an MJO event. We also do a run in which we add observed heating distributions that include the components from shallow and radiative heating. For the idealized cases, the heating input is shifted among latitude and longitude points in a manner that is consistent with the eight phases of the MJO. The CCSM4 is then run for 15 years, and the resulting MJO that is produced by all distributions is compared to that of control runs done with little or no horizontally varying heating. We perform sensitivity studies on the strength and location of heating, as well as the angle to which the tilting occurs. Preliminary results show that the addition of the shallow convective component is more important than the upper-level radiative component. We also show that the most robust MJO occurs when the tilting angle between the stratiform and mid-level convection is steeper than that of the tilting angle between the shallow and mid-level convection. A stronger MJO signal is also evident when the added heating moves southward as the MJO advances to its later phases.