A study of intraseasonal oscillations through mechanistic experiments in CAM4.0

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Wednesday, 7 January 2015
Abheera Hazra, Earth Research Institute, Santa Barbara, CA; and V. Krishnamurthy and C. Jones

The Monsoon Intraseasonal Oscillation (MISO) and the Madden Julian Oscillation (MJO) are two of the dominant elements of the tropical atmosphere exhibiting strong intraseasonal variability (ISV). They are the main components of the tropical intraseasonal oscillation (TISO). Both these events are important because of the extent of their respective influences geographically, materially in demography and economics and temporally as their subseasonality connects weather forecasts to climate predictions. This study investigates whether these principal intraseasonal oscillations (ISO) are same or different over the Indo-Pacific tropical region by using mechanistic experiments run on an atmospheric general circulation model, CAM4.0. We try to better understand the eastward propagation common to both MISO and MJO, through a few idealized experiments and experiments where observational signals are applied. In the idealized experiments a very narrow band of idealized eastward propagating heating and cooling signal is applied to the temperature tendency of CAM4.0 over the Indo-Pacific equatorial belt. In the observational experiments, observed diabatic heating MISO and MJO signals are added to CAM4.0, again over the Indo-Pacific region. These experiments are run during boreal summer (JJAS) and boreal winter (DJFM) separately. The response of temperature tendency meridionally will be discussed. The response and changes both zonally and meridionally in circulation, specific humidity and diabatic heating of the model will also be presented.