The evolution of tropical anvil clouds from their origin in deep convective cores to their slow decay determines the climatic effects of clouds in tropical convective regions. Despite the relevance of anvil clouds for climate and responses of clouds to global warming, processes dominating their evolution are not well understood. Currently available observational data reveal instantaneous snapshots of anvil cloud properties, but cannot provide a process-based perspective on anvil evolution. We therefore conduct simulations with the high resolution version of the Exascale Earth System Model in which we track mesoscale convective systems over the Tropical Western Pacific and compute trajectories that follow air parcels detrained from peaks of convective activity. With this approach we gain new insight into the anvil cloud evolution both in present day and future climate. Comparison with geostationary satellite data shows that the model is able to simulate maritime mesoscale convective systems reasonably well. Trajectory results indicate that anvil cloud lifetime is about 15 hours with no significant change in a warmer climate. The anvil ice water content is larger in a warmer climate due to a larger source of ice by detrainment and larger depositional growth leading to a more negative net cloud radiative effect along detrained trajectories. However, the increases in sources are counteracted by increases in sinks of ice, particularly snow formation and sedimentation. Furthermore, we find that the mean anvil cloud feedback along trajectories is positive and consistent with results from more traditional cloud feedback calculation methods.

Mesoscale organization of convection is typically not represented in global circulation models, and hence its influence on the global circulation is not accounted for. A parameterization aiming at representing the dynamical and physical effects of the circulation associated with organized convection, referred to as the multiscale coherent structure parameterization (MCSP), is implemented in the Energy Exascale Earth System Model version 1 (E3SMv1). Simulations are conducted to assess its impact on the simulated climate. Besides E3SMv1 simulations, we performed high-resolution (1 km) simulations using the Weather Research and Forecasting (WRF) Model to determine the temperature tendencies induced by mesoscale convective systems embedded in deep convection. We tuned the free parameters of the MCSP based on the WRF simulations. We found that the MCSP enhances Kevin wave spectra in E3SMv1, improves the representation of the Madden-Julian Oscillation, and reduces model precipitation biases over the tropical Pacific.

Historical simulations performed for the Coupled Model Intercomparison Project Phase 6 (CMIP6) used biomass burning emissions between 1997–2014 containing higher spatial and temporal variability compared to emission inventories specified for earlier years, and compared to emissions used in previous (e.g., CMIP5) simulation intercomparisons. Using the Community Earth System Model version 2 (CESM2) Large Ensemble, we show this increased biomass burning emissions variability leads to amplification of the hydrologic cycle poleward of 40°N. Notably, the high variability of biomass burning emissions leads to increased latent heat fluxes, column-integrated precipitable water, and precipitation. Lower relative humidity, greater static stability, greater ocean heat uptake, and weaker meridional energy transport from the tropics act to moderate this hydrologic cycle amplification. Our results suggest it is not only the secular changes (on multidecadal timescales) in biomass burning emissions that impact the hydrologic cycle, but also the shorter timescale variability of their emissions.

14 15 Key Points: 16 (1) E3SMv1 captures spatial and temporal variability in the observed dust aerosol optical 17 depth, but underestimates long-range transport. 18 (2) The net direct radiative effect of dust simulated by E3SMv1 is-0.42 Wm-2 with a smaller 19 longwave warming than other recent studies. 20 (3) In addition to emission, dry removal of dust are highly sensitive to the increase of 21 horizontal or vertical model resolution. 22 23 24

Clouds in the tropical western Pacific are dominated by reflective deep convective cores with gradually thinning trailing anvil clouds, which play a crucial role in determining tropical cloud radiative effects. The microphysical controls of the thinning process and its changes when subjected to a future warmer climate are still very uncertain.We use the high resolution version of the Exascale Earth System Model (E3SM) to study the thinning process in present day and future climate. We apply Lagrangian forward trajectories starting at peaks of convective activity of the detected mesoscale convective systems (MCS) and track detrained ice crystals to better understand the processes controlling the transition of a thick detrained anvil cloud into a thin cirrus cloud. The trajectories are computed offline from the 1-hourly model-calculated velocity fields and ice crystal sedimentation velocities. The modeled MCS in present day climate have a comparable time evolution to those observed by Himawari geostationary satellite data, with an average lifetime of about 10-15 hours, which accounts only for the optically thick part of the cold cloud shield. However, E3SM fails to simulate the strongest storms, which is reflected by an underestimation of albedo and overestimation of outgoing longwave radiation. The analysis of ice sources (detrainment, vapor deposition, new nucleation events) and sinks (sublimation, aggregation, sedimentation) along trajectories highlights the crucial role of the balance between depositional growth and precipitation formation for the maintenance of aging anvil clouds. Interestingly, deposition of ice on detrained ice crystals contributes to the majority of the upper tropospheric ice mass. On the other hand, about 80% of the initial cloud mass is removed in the form of precipitation within the first 10 hours of the detrainment event, changing its radiative effect from net negative to net positive. The future climate simulation shows an increase in storm frequency and intensity, an increase in ice water content and albedo in convective cores and thick anvils. The trajectory calculations reveal a 15% decrease in cloud lifetime due to climate change, suggesting a decrease in thin high clouds due to a higher precipitation efficiency and a shift to more negative net cloud radiative effects.