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Ph.D. Candidate Cao Guyu Published a Paper on Journal of Climate


Recently, DESS Ph.D. candidate Cao Guyu published a paper online as the first author called” Role of Vertical Structure of Convective Heating in MJO Simulation in NCAR CAM5.3” on Journal of Climate, with Professor Guangjun Zhang. The paper focused on the problem that almost all the global climate models are facing, the accusation of Madden Julian Oscillation simulation. By conducting several creative sensitivity experiments, the paper proposed that the lack of mesoscale stratiform heating is one of the critical reason to the poor intraseasonal osciilation simulation. The corresponding author of this paper is Professor Guangjun Zhang from Department of Earth System Science.

Madden-Julian Oscillation (MJO, Madden and Julian 1971, 1972) is a fundamental tropical process contributing to intraseasonal variability. It has been widely studied because of its significant influence on tropical and global climate and weather systems. However, it is very difficult to predict MJO accurately by global weather prediction models and to simulate it realistically by global climate models (GCMs). Failing to understand MJO thoroughly exposes gaps in our knowledge of how the atmosphere operates in the tropics. Many studies suggested that tropical large-scale circulation is sensitive to vertical structure of diabatic heating and the heating distribution should be one of the critical processes in governing the atmospheric variability.

Nowadays, none of the existing convective parameterization schemes, except one by Donner (1993), accounts for mesoscale stratiform heating. This work investigates the role of vertical heating profile in MJO simulation by modifying the convective heating profile to different shapes to mimic mesoscale heating.

Figure 1. The method of this paper

Results suggest that incorporating a mesoscale stratiform heating structure can significantly improve the MJO simulation. By artificially adding stratiform-like structure from anvil condensation heating and rain evaporative cooling in the experiments, many observed features of MJO are reproduced, including clear eastward propagation, a westward tilt vertical structure of MJO-scale anomalies of dynamic and thermodynamic fields and strong 20-80 day spectral power. Further analysis shows an abundance of shallow convection ahead of MJO deep convection, confirming the role of shallow convection in preconditioning the atmosphere by moistening the lower troposphere ahead of deep convection during MJO life cycle. All these features are lacking in the control simulation, suggesting that the mesoscale stratiform heating, especially its lower-level cooling component, is important to MJO simulation. Our results suggest the lack of the stratiform heating may be responsible for the poor MJO simulation in models.

Figure 2. The comparison of MJO models and observations.

Cao Guyu is the third year of his PhD degree in the department of Earth System Science. His research fields during PhD period are mainly focused on the evaluation and improvement of MJO in climate models, as well as deep convection parameterization scheme, which is tightly connected to cloud related processes. At the same time, He takes the student leadership positions since he enrolled in and contributes much during these three years.

Journal of Climate is the authoritative magazine in the field of the atmospheric science, according to Thomson Reuters's 2013 reference report, its impact factor is 4.90, the five-year impact factor is 4.54.