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Cronin, T. W., & Wing, A. A. (2017). Clouds, Circulation, and Climate Sensitivity in a Radiative-Convective Equilibrium Channel Model. J. Adv. Model. Earth Syst., 9(8), 2883–2905.
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He, J., & Soden, B. J. (2015). Anthropogenic Weakening of the Tropical Circulation: The Relative Roles of Direct CO[sub:2]Forcing and Sea Surface Temperature Change. J. Climate, 28(22), 8728–8742.
Abstract: There is a lack of consensus on the physical mechanisms that drive the anthropogenic weakening of tropical circulation. This study investigates the relative roles of direct CO2 forcing, mean SST warming, and the pattern of SST change on the weakening of the tropical circulation using an ensemble of AMIP and aquaplanet simulations. In terms of the mean weakening of the tropical circulation, the SST warming dominates over the direct CO2 forcing through its control over the tropical mean hydrological cycle and tropospheric stratification. In terms of the spatial pattern of circulation weakening, however, the three forcing agents are all important contributors, especially over the ocean. The increasing CO2 weakens convection over ocean directly by stabilizing the lower troposphere and indirectly via the land-sea warming contrast. The mean SST warming drives strong weakening over the centers and edges of convective zones. The pattern of SST warming plays a crucial role on the spatial pattern of circulation weakening over the tropical Pacific.The anthropogenic weakening of the Walker circulation is mostly driven by the mean SST warming. Increasing CO2 strengthens the Walker circulation through its indirect effect on land-sea warming contrast. Changes in the upper-level velocity potential indicate that the pattern of SST warming does not weaken the Walker circulation despite being El Nino-like. A weakening caused by the mean SST warming also dominates changes in the Hadley circulation in the AMIP simulations. However, this weakening is not simulated in the Southern Hemisphere in coupled simulations.
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Heath, N. K., Fuelberg, H. E., Tanelli, S., Turk, F. J., Lawson, R. P., Woods, S., et al. (2017). WRF nested large-eddy simulations of deep convection during SEAC(4)RS. J. Geophys. Res. Atmos., 122(7), 3953–3974.
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Lozier, M. S., Lozier MS, Li, F., Li F, Bacon, S., Bacon S, et al. (2019). A sea change in our view of overturning in the subpolar North Atlantic. Science, 363(6426).
Abstract: To provide an observational basis for the Intergovernmental Panel on Climate Change projections of a slowing Atlantic meridional overturning circulation (MOC) in the 21st century, the Overturning in the Subpolar North Atlantic Program (OSNAP) observing system was launched in the summer of 2014. The first 21-month record reveals a highly variable overturning circulation responsible for the majority of the heat and freshwater transport across the OSNAP line. In a departure from the prevailing view that changes in deep water formation in the Labrador Sea dominate MOC variability, these results suggest that the conversion of warm, salty, shallow Atlantic waters into colder, fresher, deep waters that move southward in the Irminger and Iceland basins is largely responsible for overturning and its variability in the subpolar basin.
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Mapes, B. E. (2016). Gregarious convection and radiative feedbacks in idealized worlds. J. Adv. Model. Earth Syst., 8(2), 1029–1033.
Abstract: What role does convection play in cloud feedbacks? What role does convective aggregation play in climate? A flurry of recent studies explores self-aggregation of moist convection in diverse simulations using explicit convection and interactive radiation. The implications involve upper level dry areas acting as infrared windowsthe climate system's radiator fins. A positive feedback maintains these: dry columns undergo radiative cooling which drives descent and further drying. If the resulting clumpiness of vapor and cloud fields depends systematically on global temperature, then convective organization could be a climate system feedback. How reconcilable and how relevant are these interesting but idealized studies?
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Miyamoto, Y., Yamaura, T., Yoshida, R., Yashiro, H., Tomita, H., & Kajikawa, Y. (2016). Precursors of deep moist convection in a subkilometer global simulation. J. Geophys. Res. Atmos., 121(20), 12,080–12,088.
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Nicholson, S. E. (2015). Evolution and current state of our understanding of the role played in the climate system by land surface processes in semi-arid regions. Global and Planetary Change, 133, 201–222.
Abstract: The role of the land surface in climate and weather has been a major research focus since the 1970s. Since that time our understanding of the issue has greatly changed and many new themes in several disciplines are being considered. This article summarizes the changes in our understanding that have taken place in research on this topic and reviews principally papers that have appeared in the last two decades. Several other papers provide comprehensive reviews of literature that appeared prior to that time. The major changes that have occurred include 1) more sophisticated and rigorous analysis of desertification, 2) increased emphasis on hydrological processes, including the role of groundwater, 3) use of multi-model ensembles and regional models, 4) the emergence of the domain of ecohydrology, with emphasis on detailed feedbacks between water availability and vegetation, 5) examination of the hypothesis that vegetation feedback can produce abrupt climate change, 6) emphasis on the impacts on convective or synoptic-scale systems, and 7) consideration of the impact of aerosols, including the Saharan Air Layer. With the exception of desertification, each of these topics is reviewed.
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Wing, A. A. (2019). Self-Aggregation of Deep Convection and its Implications for Climate. Curr Clim Change Rep, 5(1), 1–11.
Abstract: This paper reviews the self-aggregation of deep convection, its impact on the large-scale environment, its dependence on surface temperature, and its implications for climate. Self-aggregation generates significant humidity variability, dries the mean state, reduces high cloud cover, and increases the ability of the atmosphere to cool to space. Some studies find that convection is more self-aggregated at warmer temperatures but other studies, or other ways of measuring the degree of self-aggregation, disagree. There is not a simple, monotonic relationship between self-aggregation and surface temperature. Self-aggregation, through its effect on the humidity distribution and radiative budget, can affect climate. However, there is uncertainty over how strong the modulation of climate by self-aggregation is, in part because of the ambiguity over its temperature dependence. There are some indications that self-aggregation may modestly reduce climate sensitivity even without a dramatic temperature dependence, but more research is needed to understand this behavior.
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Zhu, P. (2015). On the Mass-Flux Representation of Vertical Transport in Moist Convection. J. Atmos. Sci., 72(12), 4445–4468.
Abstract: This study investigates to what extent the convective fluxes formulated within the mass-flux framework can represent the total vertical transport of heat and moisture in the cloud layer and whether the same approach can be extended to represent the vertical momentum transport using large-eddy simulations (LESs) of six well-documented cloud cases, including both deep and shallow convection. Two methods are used to decompose the LES-resolved vertical fluxes: decompositions based on the coherent convective features using the mass-flux top-hat profile and by two-dimensional fast Fourier transform (2D-FFT) in terms of wavenumbers. The analyses show that the convective fluxes computed using the mass-flux formula can account for most of the total fluxes of conservative thermodynamic variables in the cloud layer of both deep and shallow convection for an appropriately defined convective updraft fraction, a result consistent with the mass-flux dynamic view of moist convection and previous studies. However, the mass-flux approach fails to represent the vertical momentum transport in the cloud layer of both deep and shallow convection. The 2D-FFT and other analyses suggest that such a failure results from a number of reasons: 1) the complicated momentum distribution in the cloud layer cannot be well described by the simple top-hat profile; 2) shear-driven small-scale eddies are more efficient momentum carriers than coherent convective plumes; 3) the phase relationship between vertical velocity and horizontal momentum components is substantially different from that between vertical velocity and conservative thermodynamic variables; and 4) the structure of horizontal momentum can change substantially from case to case even in the same climate regime.
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