Abstract.Isca is a framework for the idealized modelling of the global circulation of planetary atmospheres at varying levels of complexity and realism. The framework is an outgrowth of models from the Geophysical Fluid Dynamics Laboratory designed for Earth's atmosphere, but it may readily be extended into other planetary regimes. Various forcing and radiation options are available, from dry, time invariant, Newtonian thermal relaxation to moist dynamics 5 with radiative transfer. Options are available in the dry thermal relaxation scheme to account for the effects of obliquity and eccentricity (and so seasonality), different atmospheric optical depths and a surface mixed layer. An idealized gray radiation scheme, a two-band scheme and a multi-band scheme are also available, all with simple moist effects and astronomically-based solar forcing. At the complex end of the spectrum the framework provides a direct connection to comprehensive atmospheric general circulation models. 10For Earth modeling, options include an aqua-planet and configurable continental outlines and topography.Continents may be defined by changing albedo, heat capacity and evaporative parameters, and/or by using a simple bucket hydrology model. Oceanic Q-fluxes may be added to reproduce specified sea-surface temperatures, with arbitrary continental distributions. Planetary atmospheres may be configured by changing planetary size and mass, solar forcing, atmospheric mass, radiative, and other parameters. Examples are given of various Earth configurations 15 as well as a Jovian simulation, a Venusian simulation, and tidally-locked and other orbitally-resonant exo-planet simulations.The underlying model is written in Fortran and may largely be configured with Python scripts. Python scripts are also used to run the model on different architectures, to archive the output, and for diagnostics, graphics, and post-processing. All of these features are publicly available on a git-based repository.
<div>Recent studies have revealed biases in sea surface temperature trends in CMIP6 between about 1970 and 2015, and other studies have suggested a possible lack of aerosol emissions over Asia in the same period. Motivated by these findings, we investigate the effect of doubling anthropogenic aerosol emissions over Asia from 1950 onward on sea surface temperatures in NorESM2-LM. While the perturbation of historical aerosol emissions does not yield a robust improvement in modeled sea surface temperature trends, we discover other changes which are worthy of further investigation:&#160;</div><div>&#160;</div><ul><li>We find that the ocean heat transport decreases significantly in the Northern Hemisphere extratropics, which is counter-intuitive given the increasing temperature gradient between the tropics and the polar regions due to the enhanced aerosol emissions.</li> <li>When doubling SO<sub>2</sub> emissions, we find increases in Southern Hemisphere sea surface temperatures in contrast to cooling in the Northern Hemisphere.&#160;</li> </ul><p><span></span><span></span></p><div>Furthermore, we compare the fully-coupled simulations to atmosphere-only simulations where historical sea surface temperatures are prescribed and the same perturbation of aerosol emissions over Asia is imposed. The atmosphere-only simulations show much weaker changes in cloud cover compared to the fully-coupled simulations. Hence, sea surface temperature changes &#8211; possibly caused by changes in the oceanic circulation &#8211; must play an important role in setting the atmospheric response.</div>
Contents of this file This document includes seven figures to supplement the main text.
Clouds are the main source of uncertainties when projecting climate change. Mixed-phase clouds (MPCs) that contain ice and supercooled-liquid particles are especially hard to constrain, and climate models neither agree on their phase nor their spatial extent. This is problematic, as models that underestimate contemporary supercooled-liquid in MPCs will underestimate future warming. Furthermore, it has recently been shown that supercooled-liquid water in MPCs is not homogeneously-mixed, neither vertically nor horizontally. However, while there have been attempts at observationally constraining MPCs to constrain uncertainties in future warming, all studies only use the phase of the interior of MPCs. Using novel satellite observations, and contrary to current knowledge, we show that MPCs are more liquid at the cloud top globally. We use these observations to constrain, for the first time, the cloud top phase in addition to the interior of MPCs in a global climate model, leading to +1C more 21st century warming in NorESM2 SSP5-8.5 climate projections. We anticipate that the difference between cloud top and interior phase in MPCs is an important new target metric for future climate model development, because similar MPC-related biases in future warming are likely present in many climate models.
Dear referee Takao Kawasaki, Thank you for your comments on our manuscript. Concerning the inter annual variability, we will include a more detailed comparison to other observation-based studies in our revised manuscript to discuss whether the values for our study period are representative or not. We can also compare the reanalysis value (145 TW) to a longer time series from the reanalysis (C-GLORS).C1
Interactive comment on "Volume and temperature transports through the main Arctic Gateways: A comparative study between an ocean reanalysis and mooring-derived data" by Marianne Pietschnig et al. Dear Matthew Hecht, Dear Referees, Dear Prof. Schauer, Thank you very much for taking the time to read our manuscript and contribute to the online discussion. We especially thank the reviewers for their insightful and constructive comments, which are a great guidance for our revision and will help to improve the quality of our manuscript. We will submit a revised manuscript in which we aim to address all comments raised by the reviewers. Below we include a more detailed list C1 OSD Interactive commentPrinter-friendly version Discussion paper
From a climate perspective, land differs from the ocean in several fundamental physical ways, including albedo, heat capacity, amount of water storage, and differences in resistance to evaporation. These differences alter the surface energy and water budgets over land compared to ocean, with implications for both surface climate and atmospheric circulation. In this study, we use an idealized general circulation model (Isca) to explore the climate state of Northland, a planet with a northern land hemisphere and a southern ocean hemisphere. These idealized simulations are motivated by the asymmetry of continental distribution on the globe, with a greater concentration of landmasses in the northern hemisphere and a larger area of ocean in the southern hemisphere, and further illuminate the basic role that land-sea contrasts play in global atmospheric dynamics. We find a much larger seasonal cycle of temperature over land compared to ocean, as expected. The continent is seasonally wet in the tropics, has a subtropical desert, and a moist high-latitude ``swamp'', where moisture transported from the tropics accumulates. Decreasing the land albedo leads to warming. In contrast to past studies, suppressing evaporation from the land surface cools the climate, resulting from decreased atmospheric water vapor and reduced trapping of longwave radiation, which dominates over the warming associated with reduced evaporative cooling at the surface. The ITCZ in the Northland simulations extends farther polewards over both the land and ocean hemispheres than the ITCZ in an aquaplanet. Our results demonstrate the potential for land and hemispheric asymmetries in controlling the large-scale axisymmetric atmospheric circulation.
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