Aiko Voigt

University of Vienna | UniWien · Institut für Meteorologie und Geophysik

Previous modeling work showed that aerosol can affect the position of the tropical rain belt, i.e., the intertropical convergence zone (ITCZ). Yet, it remains unclear which aspects of the aerosol impact are robust across models, and which are not. Here, we present simulations with seven comprehensive atmosphere models that study the fast and slow i...

Climate models robustly project that global warming will lead to a poleward shift of the annual-mean zonal-mean extratropical jet streams. The magnitude of such shifts remains uncertain, however, and recent work has indicated a potentially important role of cloud radiative interactions. The model spread found in realistic simulations with interacti...

This paper introduces the Tropical Rain belts with an Annual cycle and a Continent Model Intercomparison Project (TRACMIP). TRACMIP studies the dynamics of tropical rain belts and their response to past and future radiative forcings through simulations with 13 comprehensive and one simplified atmosphere models coupled to a slab ocean and driven by...

The atmospheric circulation controls how global climate change will be expressed regionally. Substantial circulation changes are expected under global warming, including a narrowing of the intertropical convergence zone, a slow down and poleward expansion of the tropical circulation, and a poleward shift of mid-latitude stormtracks and jets. Yet, c...

Extratropical cyclones are storm systems that are observed to travel preferentially within confined regions known as storm tracks. They contribute to precipitation, wind and temperature extremes in mid-latitudes. Cyclones tend to form where surface temperature gradients are large, and the jet stream influences their speed and direction of travel. S...

Cloud radiative heating (CRH) within the atmosphere affects the dynamics and predictability of extratropical cyclones. However, CRH is uncertain in numerical weather prediction and climate models, and this could affect model predictions of extratropical cyclones. In this paper, we present a systematic quantification of CRH uncertainties. To this en...

We present baroclinic life‐cycle simulations with two versions of the atmosphere model ICON to understand how cloud‐radiative heating and cooling affect an idealized midlatitude cyclone. Both versions simulate the same cyclone when run without radiation, but disagree when cloud‐radiation‐interaction is taken into account. The radiative effects of c...

Cloud-radiative heating (CRH) within the atmosphere and its changes with warming affect the large-scale atmospheric winds in a myriad of ways, such that reliable predictions and projections of circulation require reliable calculations of CRH. In order to assess the sensitivities of upper-tropospheric midlatitude CRH to model settings, we perform a...

Cloud-radiative heating (CRH) within the atmosphere and its changes with warming affect the large-scale atmospheric wind patterns in a myriad of ways, such that reliable predictions and projections of circulation require reliable calculations of CRH. In order to assess sensitivities of upper-tropospheric midlatitude CRH to model settings, we perfor...

Extratropical cyclones drive midlatitude weather, including extreme events, and determine midlatitude climate. Their dynamics and predictability are strongly shaped by cloud diabatic processes. While the cloud impact due to latent heating is much studied, little is known about the impact of cloud radiative heating (CRH) on the dynamics and predicta...

We generate trajectories in storm‐resolving simulations in order to quantify the effect of ice microphysics on tropical upper‐tropospheric cloud‐radiative heating. The pressure and flow field tracked along the trajectories are used to run different ice microphysical schemes, both one‐ and two‐moment formulations within the Icosahedral Non‐hydrostat...

Warm conveyor belts are important features of extratropical cyclones and are characterized by active diabatic processes. Previous studies reported that simulations of extratropical cyclones can be strongly impacted by the horizontal grid spacing. Here, we study to what extent and in which manner simulations of warm conveyor belts are impacted by th...

We present a new method to identify connected components on triangular grids used in atmosphere and climate models to discretize the horizontal dimension. In contrast to structured latitude–longitude grids, triangular grids are unstructured and the neighbors of a grid cell do not simply follow from the grid cell index. This complicates the identifi...

Snowball Earth is a hypothesized state in the deep past of Earth in which the ocean was completely or nearly completely covered by sea ice, resulting from a runaway ice‐albedo feedback. Here, we address how the treatment of sea‐ice thermodynamics affects the initiation of a Snowball Earth in the global climate model ICON‐A run in an idealized slab‐...

Waterbelt climate states with an ice-free tropical ocean provide a straightforward explanation for the survival of advanced marine species during the Cryogenian glaciations (720–635 million years ago). Previous work revealed that stable waterbelt states require the presence of highly reflective low-level mixed-phase clouds with a high abundance of...

Extratropical cyclones drive midlatitude weather, including extreme events, and determine midlatitude climate. Their dynamics and predictability are strongly shaped by cloud diabatic processes. While the cloud impact due to latent heating is much studied, little is known about the impact of cloud radiative heating (CRH) on the dynamics and predicta...

Geological evidence of active tropical glaciers reaching sea level during the Neoproterozoic (1,000–541 Ma), suggesting a global ocean completely covered in ice, was the key observation in the development of the hard Snowball Earth hypothesis. These conditions are hard to reconcile with the survival of complex marine life through Snowball Earth gla...

The TRACMIP (Tropical Rain Belts with an Annual Cycle and Continent Model Intercomparison Project) ensemble includes slab-ocean aquaplanet control simulations and experiments with a highly idealized narrow tropical continent (0°–45°W, 30°S–30°N). We compare the two setups to contrast the characteristics of oceanic and continental rainbands and inve...

Warm conveyor belts are important features of extratropical cyclones and are characterized by active diabatic processes. Previous studies reported that the simulation of extratropical cyclones can be strongly impacted by horizontal model resolution. Here, we study to what extent and in which manner simulations of warm conveyor belts are impacted by...

We present a new method to identify connected components on a triangular grid. Triangular grids are, for example, used in atmosphere and climate models to discretize the horizontal dimension. Because they are unstructured, neighbor relations are not self-evident and identifying connected components is challenging. Our method addresses this challeng...

The North Atlantic jet stream is projected to extend eastward towards Europe in boreal winter in response to climate change. We show that this response is robust across a hierarchy of climate models and climate change scenarios. We further show that cloud-radiative changes contribute robustly to the eastward extension of the jet stream in three atm...

Simulations of the global climate system at storm-resolving resolutions of 2 km are now becoming feasible and show promising realism in clouds and precipitation. However, shortcomings in their representation of microscale processes, like the interaction of cloud droplets and ice crystals with radiation, can still restrict their utility. Here, we il...

The Tropical Rain belts with an Annual cycle and Continent Model Intercomparison Project (TRACMIP) ensemble includes slab-ocean aquaplanet controls and experiments with a highly idealized tropical continent: modified aquaplanet grid cells with increased evaporative resistance, increased albedo, reduced heat capacity, and no ocean heat transport (ze...

The intertropical convergence zone (ITCZ) is an important component of the tropical rain belt. Climate models continue to struggle to adequately represent the ITCZ and differ substantially in its simulated response to climate change. Here we employ complex network approaches, which extract spatiotemporal variability patterns from climate data, to b...

By interacting with radiation, clouds modulate the flow of energy through the Earth system, the circulation of the atmosphere, and regional climate. We review the impact of cloud‐radiation interactions for the atmospheric circulation in the present‐day climate, its internal variability and its response to climate change. After summarizing cloud‐con...

The intertropical convergence zone (ITCZ) is an important component of the tropical rain belt. Climate models continue to struggle to adequately represent the ITCZ and differ substantially in its simulated response to climate change. Here we employ complex network approaches, which extract spatio-temporal variability patterns from climate data, to...

Clouds interact with atmospheric radiation and substantially modify the Earth's energy budget. Cloud formation processes occur over a vast range of spatial and temporal scales, which make their thorough numerical representation challenging. Therefore, the impact of parameter choices for simulations of cloud‐radiative effects is assessed in the curr...

Previous studies showed that global cloud-radiative changes contribute half or more to the midlatitude atmospheric circulation response to global warming. Here, we investigate the relative importance of tropical, midlatitude, and polar cloud-radiative changes for the annual-mean, wintertime, and summertime circulation response across regions in AMI...

Clouds shape weather and climate by regulating the latent and radiative heating in the atmosphere. Recent work demonstrated the importance of cloud‐radiative effects (CRE) for the mean circulation of the extratropical atmosphere and its response to global warming. In contrast, little research has been done regarding the impact of CRE on internal va...

More than one hundred days were simulated over very large domains with fine (0.156 km to 2.5 km) grid spacing for realistic conditions to test the hypothesis that storm (kilometer) and large-eddy (hectometer) resolving simulations would provide an improved representation of clouds and precipitation in atmospheric simulations. At scales that resolve...

Plain Language Summary Clouds are an important component of the climate system. They modify the atmospheric circulation via radiative heating and cooling, both in the present‐day climate and in future climates. We compare two methods that aim at diagnosing how radiative changes in clouds, which occur as part of climate change (i.e., cloud feedbacks...

The Tropical Rain bands with an Annual cycle and Continent Model Intercomparison Project (TRACMIP) ensemble—a multi-model ensemble of slab-ocean simulations in idealized configurations—provides a test of the relationship between the zonal mean ITCZ and the cross-equatorial atmospheric energy transports (AHT eq ). In a gross sense, the ITCZ position...

Abstract Previous work demonstrated the strong radiative coupling between clouds and the midlatitude circulation. Here we investigate the impact of cloud‐radiative changes on the global warming response of the midlatitude jet streams and storm tracks in the North Atlantic, North Pacific, and Southern Hemisphere. To this end, we use the ICOsahedral...

In this review, we highlight the complementary relationship between simple and comprehensive models in addressing key scientific questions to describe Earth's atmospheric circulation. The systematic representation of models in steps, or hierarchies, connects our understanding from idealized systems to comprehensive models and ultimately the observe...

A new release of the Max Planck Institute for Meteorology Earth System Model version 1.2 (MPI-ESM1.2) is presented. The development focused on correcting errors in and improving the physical processes representation, as well as improving the computational performance, versatility, and overall user friendliness. In addition to new radiation and aero...

Previous work showed that the poleward expansion of the annual-mean zonal-mean atmospheric circulation in response to global warming is strongly modulated by changes in clouds and their radiative heating of the surface and atmosphere. Here, a hierarchy and an ensemble of global climate models are used to study the circulation impact of changes in a...

The impact of cloud-radiative interactions on the tropical circulation and its response to surface warming are studied in aquaplanet model simulations with prescribed sea-surface temperatures from eight global atmosphere models. Simulations with enabled and disabled cloud-radiative interactions are compared. In a present-day-like climate, the prese...

Recent analyses of global climate models suggest that uncertainty in the coupling between midlatitude clouds and the atmospheric circulation contributes to uncertainty in climate sensitivity. However, the reasons behind model differences in the cloud-circulation coupling have remained unclear. Here, we use a global climate model in an idealized aqu...

Global constraints on momentum and energy govern the variability of the rainfall belt in the intertropical convergence zone and the structure of the zonal mean tropical circulation. The continental-scale monsoon systems are also facets of a momentum- and energy-constrained global circulation, but their modern and palaeo variability deviates substan...

Mid-latitude cyclones are strongly affected by diabatic processes. While the importance of latent heating is well established, the role of radiation has received little attention. Here, we address this question for idealized cyclones by performing baroclinic life cycle simulations in the global atmosphere model ICON with and without radiation, and...

Geological evidence indicates that grounded ice sheets reached sea level at all latitudes during two long-lived Cryogenian (58 and ≥5 My) glaciations. Combined uranium-lead and rhenium-osmium dating suggests that the older (Sturtian) glacial onset and both terminations were globally synchronous. Geochemical data imply that CO 2 was 10 2 PAL (presen...

We analyze the source of inter-model scatter in the surface temperature response to quadrupling CO2 in two sets of GCM simulations from the Tropical Rain Belts with an Annual cycle and a Continent Model Intercomparison Project (TRACMIP; Voigt et al, 2016). TRACMIP provides simulations of idealized climates that allow for studying the fundamental dy...

The region of tropical convective precipitation (the ITCZ) migrates by approximately 12° of latitude over the seasonal cycle with an annual mean position slightly north of the equator. We demonstrate that the ITCZ is located in the hemisphere in which the atmosphere is heated more strongly. A 3° latitude ITCZ shift requires approximately 1 PW of en...

In Atmospheric General Circulation Models (AGCMs) direct radiative forcing (increased CO2 with fixed sea surface temperature) is an imperfect concept because land temperatures are not fixed. Here the response to direct radiative forcing is decomposed into increased CO2 over ocean and land using an AGCM with spatially dependent CO2. The land versus...

Significance Assessing the response of clouds to global warming remains a challenge of climate science. Past research has elucidated what controls the height and temperature of high-level anvil clouds, but the factors that control their horizontal extent remained uncertain. We show that the anvil cloud amount is expected to shrink as the climate wa...

Previous research has shown that subtropical and extratropical circulations are linked seasonally and in response to climate change. In particular, amplification (weakening) of subtropical stationary eddies is linked to a poleward (equatorward) shift of the extratropical circulation in the Northern Hemisphere. Here the mechanisms linking subtropica...

Aquaplanet simulations exhibit a robust expansion of the Hadley cell and poleward jet shift in response to uniform warming of sea surface temperature. Here moist thermodynamic and dynamic frameworks are combined to make predictions of circulation responses to warming. We show Clausius-Clapeyron (CC) scaling of specific humidity with warming predict...

The energetic framework predicts no shift of the zonal mean Intertropical Convergence Zone (ITCZ) in response to zonally asymmetric forcings (zonal warming and cooling regions with zero zonal mean) assuming radiative feedbacks are linear. Here we show the ITCZ shifts southward in response to a zonally asymmetric forcing in the Northern Hemisphere s...

During summertime, monsoons and subtropical anticyclones shape precipitation and regional circulation patterns across the globe. In state-of-the-art climate models, the average response of the Asian monsoon cyclone, Pacific ocean anticyclone and jet stream to global warming is weak and responses of different models are diverse. Here we use a suite...

The connection between the large-scale tropical circulation of the atmosphere, convective mixing, and climate sensitivity is explored in a wide range of climates through a perturbed-parameter ensemble of a comprehensive Earth-System Model. Four parameters related to the representation of atmospheric moist convection are found to dominate the respon...

Whereas it is well established that clouds are important to changes in Earth's surface temperature, their impact on changes of the large-scale atmospheric circulation is less well understood. Here we study the radiative impact of clouds on the shift of the inter-tropical convergence zone (ITCZ) in response to hemispheric surface albedo forcings. Th...

Despite a substantial hemispheric asymmetry in clear-sky albedo, observations of Earth's radiation budget reveal that the two hemispheres have the same all-sky albedo. Here, aquaplanet simulations with the at-mosphere general circulation model ECHAM6 coupled to a slab ocean are performed to study to what extent and by which mechanisms clouds compen...

Equilibrium climate sensitivity (ECS) is a widely accepted measure of Earth's susceptibility to radiative forcing. While ECS is often assumed to be constant to a first order of approximation, recent studies suggested that ECS might depend on the climate state. Here it is shown that the latest generation of climate models consistently exhibits an in...

I study the Hadley circulation of a completely ice-covered Snowball Earth through simulations with a comprehensive atmosphere general circulation model. Because the Snowball Earth atmosphere is an example of a dry atmosphere, these simulations allow me to test to what extent dry theories and idealized models capture the dynamics of realistic dry Ha...

A major goal of understanding Neoproterozoic glaciations and determining their effect on the evolution of life and Earth's atmosphere is establishing whether and how much open ocean there was during them. Geological evidence tells us that continental ice sheets had to flow into the ocean near the equator during these glaciations. Here we drive the...

[1] Atmospheric circulation in a Snowball Earth is critical for determining cloud behavior, heat export from the tropics, regions of bare ice, and sea glacier flow. These processes strongly affect Snowball Earth deglaciation and the ability of oases to support photosynthetic marine life throughout a Snowball Earth. Here we establish robust aspects...

Several studies have analysed the atmospheric response to sea-ice changes in the Arctic region, but only few have considered the Antarctic. Here, the atmospheric response to sea-ice variability in the Southern Hemisphere is investigated with the atmospheric general circulation model ECHAM5. The model is forced by the present and a projected future...

[1] A radiative-convective equilibrium (RCE) configuration of a comprehensive atmospheric general circulation model, ECHAM6, is coupled to a mixed-layer ocean for the purpose of advancing understanding of climate and climate change. This configuration differs from a standard configuration only through the removal of land-surface processes, spatial...

While the concentration of landmasses and atmospheric aerosols on the Northern Hemisphere suggests that the Northern Hemisphere is brighter than the Southern Hemisphere, satellite measurements of top-of-atmosphere irradiances found that both hemispheres reflect nearly the same amount of shortwave irradiance. Here, the authors document that the most...

The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs gr...

Neoproterozoic, and possibly Paleoproterozoic, glaciations represent the most extreme climate events in post-Hadean Earth, and may link closely with the evolution of the atmosphere and life. According to the Snowball Earth hypothesis, the entire ocean was covered with ice during these events for a few million years, during which time volcanic CO2 i...

In order to understand the climate on terrestrial planets orbiting nearby Sun-like stars, one would like to know their thermal inertia. We use a global climate model to simulate the thermal phase variations of Earth-analogs and test whether these data could distinguish between planets with different heat storage and heat transport characteristics....

Identifying liquid water on the surface of planets is a high priority, as this traditionally defines habitability. One proposed signature of oceans is specular reflection ("glint"), which increases the apparent albedo of a planet at crescent phases. We post-process a global climate model of an Earth-like planet to simulate reflected lightcurves. Si...