The present study examines the characteristics of the MJO events represented in the Energy Exascale Earth System Model version 1 (E3SMv1), DOE’s new Earth system model. The coupled E3SMv1 realistically simulates the eastward propagation of precipitation and Moist Static Energy (MSE) anomalies associated with the MJO. As in observation, horizontal moisture advection and longwave radiative feedback are found to be the dominant processes in E3SMv1 that lead to the eastward movement and maintenance of the MSE anomalies, respectively. Modulation of the diurnal cycle of precipitation in the Maritime Continent region by the MJO is also well represented in the model despite systematic biases in the magnitude and phase of the diurnal cycle. On the midlatitude impact of the MJO, E3SMv1 reasonably captures the pattern of the MJO teleconnection across the North Pacific and North America, with improvement in the performance in a high-resolution version, despite the magnitude being a bit weaker than the observed feature. About interannual variability of the MJO, the El Niño-Southern Oscillation (ENSO) modulation of the zonal extent of MJO’s eastward propagation, as well as associated changes in the mean state moisture gradient in the tropical west Pacific, is well reproduced in the model. However, MJO in E3SMv1 exhibits no sensitivity to the Quasi-Biennial Oscillation (QBO), with the MJO propagation characteristics being almost identical between easterly QBO and westerly QBO years. Processes that have been suggested as critical to MJO simulation are also examined by utilizing recently developed process-oriented diagnostics.

Tropical convective systems that grow larger than 100,000km2 sizes play a significant role in the water cycle and energy budget of the Earth system. Previously, we developed hybrid tropical cloud-precipitation regimes (TCPRs) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) cloud observations and Integrated Multi-satellitE Retrievals for GPM (IMERG) precipitation data at a 1° scale, and demonstrated that TCPRs enabled a simple but effective identification of convective systems at the synoptic scale. The Madden-Julian Oscillation (MJO) is the dominant mode of tropical intraseasonal variability, which is characterized as a planetary-scale envelop of convective clouds that propagates eastward over the Indo-Pacific warm pool. Recent studies showed a statistically robust correlation between the MJO and the quasi-biennial oscillation (QBO); MJO-related convective activities are enhanced and suppressed during an easterly and westerly phase of QBO, respectively. While the underlying mechanism of the MJO-QBO relationship has remained elusive, one of the most popular hypotheses is that the weakened stability in the upper troposphere and lower stratosphere during easterly QBO years provides a preferrable condition for deep convection to develop deeper and persist longer. To test the stability hypothesis for the QBO control on the MJO, we examine properties of the convective aggregates of TCPRs in the southern Maritime Continent region, in which the contrast in MJO activities between easterly and westerly QBO years is most pronounced. By taking advantage of TCPRs, we composite the total size, fractions of stratiform clouds to core area, and top height of core for different phases of MJO and QBO, and the results are compared to find any systematic difference in the characteristics of convective aggregates. Our results show that, as consistent to previous studies, bigger convective aggregates tend to occur when the stability weakens. Further insight will be obtained by examining cloud radiative effects and atmospheric energy budget per convective aggregates.

The next-generation global climate model from the NASA Goddard Institute for Space Studies, GISS-E3, contains many improvements to resolution and physics that allow for improved representation of tropical cyclones (TCs) in the model. This study examines the properties of TCs in two different versions of E3 at different points in its development cycle, run for 20 years at 0.5 degree resolution, and compares these TCs with observations, the previous generation GISS model, E2, and other climate models. E3 shares many TC biases common to global climate models, such as having too few tropical cyclones, but is much improved from E2. E3 produces strong enough TCs that observation-based wind speed thresholds can now be used to detect and track them, and some storms now reach hurricane intensity; neither of these was true of E2. Model development between the first and second versions of E3 further increased the number and intensity of TCs and reduced TC count biases globally and in most regions. One-year sensitivity tests to changes in various microphysical and dynamical tuning parameters are also examined. Increasing the entrainment rate for the more strongly entraining plume in the convection scheme increases the number of TCs (though also affecting other climate variables, and in some cases increasing biases). Variations in divergence damping did not have a strong effect on simulated TC properties, contrary to expectations based on previous studies. Overall, the improvements in E3 make it more credible for studies of TC activity and its relationship to climate.

This study examines the role of the mean state in the propagation of the Madden-Julian Oscillation (MJO) over the Maritime Continent (MC). We use an ensemble of simulations made with a single model - the Community Earth System Model version 2 (CESM2) – to assess the effect of the mean state that is unaffected by that of model components such as parameterization schemes. Results show that one ensemble member with an exceptionally stronger MJO propagation also exhibits a much steeper background meridional moisture gradient (MMG) over the southern MC region than the other ensemble members. The simulated mean state affects MJO via its impacts on moisture dynamics - a column water vapor budget reveals a greater advection of mean moisture by MJO wind in the southern MC is responsible for the anomalous MJO activity.