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Mitovski, T, Cole JNS, McFarlane NA, Von Salzen K, Zhang GJ.  2019.  Convective response to large-scale forcing in the tropical western Pacific simulated by spCAM5 and CanAM4.3. Geoscientific Model Development. 12:2107-2117.   10.5194/gmd-12-2107-2019   AbstractWebsite

Changes in the large-scale environment during convective precipitation events in the tropical western Pacific simulated by version 4.3 of the Canadian Atmospheric Model (CanAM4.3) are compared against those simulated by version 5.0 of the super-parameterized Community Atmosphere Model (spCAM5). This is done by compositing sub-hourly output of convective rainfall, convective available potential energy (CAPE), CAPE generation due to large-scale forcing in the free troposphere (dCAPELSFT) and near-surface vertical velocity (omega) over the time period May-July 1997. Compared to spCAM5, CanAM4.3 tends to produce more frequent light convective precipitation (< 0.2 mm h(-1)) and underestimates the frequency of extreme convective precipitation (> 2 mm h(-1)). In spCAM5, 5% of convective precipitation events lasted less than 1.5 h and 75% lasted between 1.5 and 3.0 h, while in CanAM4.3 80% of the events lasted less than 1.5 h. Convective precipitation in spCAM5 is found to be a function of dCAPE(LSFT) and the large-scale near-surface omega with variations in omega slightly leading variations in convective precipitation. Convective precipitation in CanAM4.3 does not have the same dependency and instead is found to be a function of CAPE.

Mu, MQ, Zhang GJ.  2006.  Energetics of Madden-Julian oscillations in the National Center for Atmospheric Research Community Atmosphere Model version 3 (NCAR CAM3). Journal of Geophysical Research-Atmospheres. 111   10.1029/2005jd007003   AbstractWebsite

This study analyzes the tropical intraseasonal variability and associated Madden-Julian oscillations (MJO) simulated in the National Center for Atmospheric Research Climate Model CAM3 using two versions of the Zhang-McFarlane convection scheme. The results are compared with those from the Xie-Arkin observations and European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis. It is shown that modifications to the convection scheme in the model lead to substantial enhancement of the intraseasonal variability and MJO. The spatial scale of the precipitation anomalies associated with intraseasonal variability and MJO is also in better agreement with the Xie-Arkin observations and ECMWF reanalysis. By contrast the intraseasonal variability and MJO in the CAM3 are weak. The analysis of the energetics of intraseasonal variability shows that perturbation kinetic energy (PKE) and its sources and sinks through conversion from potential energy and mean flow and generation from wave energy flux are too strong in the modified CAM3 and too weak in the CAM3 when compared with the reanalysis. It also shows that different mechanisms are responsible for the PKE production in different locations. In convectively active regions, conversion from potential energy and vertical transport are important to the maintenance of the upper troposphere PKE; in convectively suppressed regions, horizontal wave energy flux convergence and barotropic conversion are important. The interaction between convection and large-scale circulation plays an important role in the maintenance of intraseasonal variability and MJO through PKE conversion from potential energy generated by convective heating.

Mu, MQ, Zhang GJ.  2008.  Energetics of Madden Julian oscillations in the NCAR CAM3: A composite view. Journal of Geophysical Research-Atmospheres. 113   10.1029/2007jd008700   AbstractWebsite

This study further examines the simulation of the tropical Madden-Julian oscillation (MJO) using the modified Zhang-McFarlane convection scheme in the National Center for Atmospheric Research Community Atmospheric Model version 3 (CAM3). The results demonstrate that modifications to the Zhang-McFarlane scheme lead to significantly enhanced MJO and much improvement of the MJO structures. However, the propagation speed is too fast compared to observations. The westward tilting structures of moisture flux convergence over the western Pacific warm pool are simulated very well by the modified CAM3 (CAM3m). The modified Zhang-McFarlane convection scheme also improves the energetic structures of the MJOs. With the climatological mean of the energetics from the composite MJO removed, the energy budget terms show clear eastward propagation following MJO movement in the CAM3m and ECMWF reanalysis (ERA40). The results further support that the interaction between convection and largescale circulation is important in the maintenance and growth of the MJO through perturbation kinetic energy (PKE) conversion from perturbation available potential energy (PAPE) generated by the correlation of specific volume (alpha) and large-scale heating (Q(1)). Too weak Q(1) and PAPE generated through (alpha, Q(1)) is responsible for the weak MJO and intraseasonal variability simulated by the standard CAM3. Too strong climatology mean of the energetics in the CAM3m may be caused by too strong stationary intraseasonal variability. Moisture flux convergence is responsible for the changes of specific humidity in the CAM3m and CAM3 during the cycle of the MJO over the Indian and western Pacific Oceans. These results indicate that interaction between convection, moisture and convergence in the lower troposphere may be responsible for the MJO development over the Indian and western Pacific Ocean in both observations and simulations. The weak intraseasonal variability and MJO simulated by the original Zhang-McFarlane deep convection scheme is attributed to the lack of coherent shallow convection ahead of deep convection in the MJO cycle.