Self-Aggregation of Deep Convection and its Implications for Climate The original version of this article contained a mistake. In the recently published paper, “Self-Aggregation of Deep Convection and its Implications for Climate”, there was an error in Eq. 1, as a “+” was inadvertently dropped before the final portion of the equation.

Global Cloud-Resolving Models Abstract Purpose of Review Global cloud-resolving models (GCRMs) are a new type of atmospheric model which resolve nonhydrostatic accelerations globally with kilometer-scale resolution. This review explains what distinguishes GCRMs from other types of models, the problems they solve, and the questions their more commonplace use is raising. Recent Findings GCRMs require high-resolution discretization over the sphere but can differ in many other respects. They are beginning to be used as a main stream research tool. The first GCRM intercomparison studies are being coordinated, raising new questions as to how best to exploit their advantages. Summary GCRMs are designed to resolve the multiscale nature of moist convection in the global dynamics context, without using cumulus parameterization. Clouds are simulated with cloud microphysical schemes in ways more comparable to observations. Because they do not suffer from ambiguity arising from cumulus parameterization, as computational resources increase, GCRMs are the promise of a new generation of global weather and climate simulations.

Observing Changes in Ocean Carbonate Chemistry: Our Autonomous Future Abstract Purpose of Review We summarize recent progress on autonomous observations of ocean carbonate chemistry and the development of a network of sensors capable of observing carbonate processes at multiple temporal and spatial scales. Recent Findings The development of versatile pH sensors suitable for both deployment on autonomous vehicles and in compact, fixed ecosystem observatories has been a major development in the field. The initial large-scale deployment of profiling floats equipped with these new pH sensors in the Southern Ocean has demonstrated the feasibility of a global autonomous open-ocean carbonate observing system. Summary Our developing network of autonomous carbonate observations is currently targeted at surface ocean CO2 fluxes and compact ecosystem observatories. New integration of developed sensors on gliders and surface vehicles will increase our coastal and regional observational capability. Most autonomous platforms observe a single carbonate parameter, which leaves us reliant on the use of empirical relationships to constrain the rest of the carbonate system. Sensors now in development promise the ability to observe multiple carbonate system parameters from a range of vehicles in the near future.

Convection and Climate: What Have We Learned from Simple Models and Simplified Settings? Abstract Purpose of Review We ask what fundamental insights about the relationship of tropical convection to climate have arisen from recent investigations using simplified models. Recent Findings The vertical distribution of relative humidity should remain approximately constant in a changed climate. The temperature of clouds in the upper troposphere should also remain effectively constant for climate changes likely to occur in response to human-induced warming. The fractional coverage of convective clouds will likely decrease slightly with warming, but it is not known how the albedo and net radiative effect of tropical convective clouds will change. The areal extent and net radiative effect of tropical convective clouds depend on the interactions of radiation, cloud physics, and turbulence within the extended upper-level ice clouds. SST gradients develop naturally as a result of the aggregation of convection and large-scale thermodynamics and circulation act to couple the cloud properties and the SST. Summary Radiative-convective equilibrium continues to provide insight into the structure and energy balance of the atmosphere by incorporating the interactions among radiation, cloud physics, and atmospheric motion.

The Eurasian Jet Streams as Conduits for East Asian Monsoon Variability Abstract Purpose of Review This article gives a brief review on how the jet streams over the Eurasian continent influence the East Asian monsoon on intraseasonal to interdecadal time scales and discusses the seasonal predictability and change. Recent Findings The wave train along the Eurasian jet streams is found to be crucial for East Asian monsoon variability. Interaction of the upper-level Rossby wave train with the Siberian High causes changes in winter monsoon climate over East Asia. In the case of summer, the Silk Road pattern, embedded in the Asian jet in association with western North Pacific circulation and the Pacific-Japan pattern, alters the strength and phase of the monsoon. Current coupled models showed limited skills in seasonal prediction of the Eurasian jet variations and their influences on the East Asian monsoon variability. Summary The Eurasian jets as conduits for East Asian monsoon variability involve multiple feedbacks. Its interaction with low-level circulation mostly determines the degree of strength of variations in the monsoon climate. Global warming projections based on RCP 4.5 and 8.5 in the CMIP5 (the Coupled Model Intercomparison Project phase 5) models indicate that the mean Asian jet strengthens in future during winter, but no change is reported during summer.

Carbon Cycling in Global Drylands Abstract Purpose of Review The aim of this paper is to describe the carbon cycle in drylands in relation to the processes, factors, and causes affecting it. A specific focus is placed on both biotic and abiotic mechanisms of carbon sequestration in drylands in relation to mitigation of the anthropogenic climate change. Recent Findings Global dryland area is increasing along with an increase in risks of desertification, salinization, and eolian/hydrologic processes of accelerated soil erosion with strong impacts on the carbon cycle. Nonetheless, drylands contribute strongly towards the land-based sink of the atmospheric carbon dioxide through sequestration of carbon in the soil, ground water, and biomass. Thus, dryland ecosystems affect inter-annual variability in the global carbon cycle and create a negative feedback through carbon sequestration. Summary Global drylands, covering 66.7 M km2 or 45.36% of the Earth’s land area, strongly impact the ecosystem carbon stock, contribute to the land-based carbon sink, and provide a negative feedback to the global carbon cycle. Whereas the net primary productivity is limited by the water scarcity, especially in hyper-arid and arid ecoregions, sequestration of inorganic carbon in soil and ground water is an important control of the carbon cycle. Desertification, caused by eolian and hydrologic erosion along with salinization, must be controlled and reversed to enhance carbon sequestration, achieve land degradation neutrality, and create a negative feedback. Carbon sequestration strategy recognizes “soil” as a rights holder to be protected, restored and naturally evolve.

Theories for Past and Future Monsoon Rainfall Changes Abstract Purpose of Review Long-standing biases in simulations of past and present climate states and climate model disagreement even in sign of future monsoon rainfall changes evince limitations in our theoretical understanding. Recent Findings The dominant theoretical paradigms for understanding monsoon rainfall—convective-quasi equilibrium (CQE), the moist static energy (MSE) budget, and monsoons as local Intertropical Convergence Zone (ITCZ) shifts—all jettison the traditional “land-sea breeze” paradigm. Summer monsoon precipitation falls when the assumptions of CQE are most satisfied but those of the ITCZ shift framework are least satisfied. Zonal asymmetries, changes in ITCZ width and strength, hydrology-vegetation-CO2 coupling, and timescale-dependent responses complicate inferences of monsoon rainfall from paleoclimate proxy records. The MSE budget framework applied to deliberately designed simulations can illuminate key mechanisms underlying monsoon responses to external forcings, presenting a path toward falsifying model projections. Summary Sustained, rapid progress in monsoon rainfall theory is urgently needed by society and is plausible based on recent advances.

Contemporary Climate Change of the African Monsoon Systems Abstract Purpose of Review Our current understanding of current climate change in the West African, East African, and Congo Basin monsoon systems is reviewed. The detection of observed trends, the analysis of the physical processes of change, and model projections are discussed. Recent Findings An increase in Sahel precipitation has been associated with a summer intensification and northward shift of the West African monsoon system as a response to amplified warming over the Sahara. Declines in the boreal spring rains over East Africa, and in spring and summer rains in the Congo Basin, are also reported in the literature but with less corroboration through physical analysis and model projections. Confident analysis and accurate simulation are hampered by a relative scarcity of observations in these regions. Summary The West African monsoon system is trending to bring more precipitation to the Sahel in summer, and some is delivered through increasingly intense rainfall events. It is not yet clear whether recent trends observed in the East African and Congo Basin monsoon systems can be expected to persist as the global climate continues to warm. We cannot expect these monsoon systems to change linearly through the twenty-first century because, as the ocean basins warm at different rates and with different distributions, different forcing factors may become dominant.

Current and Future Variations of the Monsoons of the Americas in a Warming Climate Abstract Purpose of Review Understanding the details of the impact of global warming on the North and South America monsoons is of key importance for the well-being of a great number of inhabitants of the Americas. This review deals with the latest research on this topic. Recent Findings Combined multiple datasets, high-resolution global climate models and regional convection–permitting models provide new insights on the evolution of the North and South American monsoons under global warming, suggesting a precipitation reduction in the North American Monsoon, the southward shift of the core of the South American Monsoon, and precipitation reduction in the Amazon Basin. These changes are accompanied by increased frequency of extreme precipitation events in both monsoon regions. Summary Uncertainty in the response mechanisms to global warming remains high, especially for the North American monsoon. To make progress, the evaluation of local and remote drives is critical, for which we need a combined use of regional and global models.

Aquaplanet Simulations of Tropical Cyclones Abstract Purpose of Review Tropical cyclones (TCs) are strongly influenced by the large-scale environment of the tropics and will, therefore, be modified by climate changes. Numerical simulations designed to understand the sensitivities of TCs to environmental changes have typically followed one of two approaches: single-storm domain sizes with convection-permitting resolution and uniform thermal boundary conditions or comprehensive global high-resolution (about 50 km in the horizontal) atmospheric general circulation model (GCM) simulations. The approaches reviewed here rest between these two and are an important component of hierarchical modelling of the atmosphere: aquaplanet TC simulations. Recent Findings Idealized model configurations have revealed controls on equilibrium TC size in large-domain simulations of rotating radiative-convective equilibrium. Simulations that include differential rotation (spherical geometry) but retain uniform thermal forcing have revealed a new mechanism of TC propagation change via storm-scale dynamics and show a poleward shift in genesis in response to warming. Simulations with Earth-like meridional thermal forcing gradients have isolated competing influences on TC genesis via shifts in the atmospheric general circulation and the temperature dependence of TC genesis in the absence of mean circulation changes. Summary Aquaplanet simulations of TCs with variants that include or inhibit certain processes have recently emerged as a research methodology that has advanced the understanding of the climatic controls on TC activity. Looking forward, idealized boundary condition model configurations can be used as a bridge between GCM resolution and convection-permitting resolution models and as a tool for identifying additional mechanisms through which climate changes influence TC activity.