We employ a high-resolution Köppen climate classification dataset to examine shifts in Tundra zon... more We employ a high-resolution Köppen climate classification dataset to examine shifts in Tundra zones within the Alps and Asia. Our analysis shows substantial reductions in Tundra areas by the mid-21st century under different Shared. Socioeconomic pathways (SSP1-2.6, SSP3-7.0, SSP5-8.5). Tundra zones in the Alps and the Tibetan Plateau are crucial for their unique climates and role as water reservoirs. Characterized by short, mild summers and long, severe winters, these zones are vital for the glaciers and perennial snow. The projected climate instability may significantly reduce alpine snow cover by mid-century with irreversible consequences. A 2 C temperature increase from the 1981-2010 baseline could eliminate the Tundra climate in the Alps and reduce it by over 70% in Asia. This is particularly concerning given that rivers from the Tibetan Plateau sustain nearly 40% of the global population.
A detailed investigation of linear instabilities of double-eyewall hurricane-like vortices with d... more A detailed investigation of linear instabilities of double-eyewall hurricane-like vortices with double maxima (“walls”) of azimuthal velocity and vorticity around the central minimum (“eye”) and of their nonlinear saturation is carried out in the framework of the moist-convective rotating shallow water model. It is shown that developing barotropic instability leads to inward displacement and gradual disappearance of the inner wall and to the formation of a nontrivial tripolar quasi-stationary structure, provided the second, outer, wall of the initial vortex is high enough. The effects of moist convection lead to the enhancement of the outer wall. In comparison, under the influence of the same instability, vortices with an inner wall stronger than the outer one evolve toward monopolar single-eyewall structures.
Central Asia (CA) is among the world's most vulnerable regions to climate change. Increasing anth... more Central Asia (CA) is among the world's most vulnerable regions to climate change. Increasing anthropogenic greenhouse gas concentrations (GHGs) are the primary forcing of the current and future climate system for the time scale of a century. By analysing observation datasets, we show that a warming of 1.2 C led to a decrease of 20% in snow-depth CA during the last 70 years, especially over the mountains. In recent decades, longer summer times and fewer icing days (more than 20 daysÁyear −1) have exposed unprecedented shock to CA's climate system's components. Furthermore, we analyse 442 model ...
In this discourse, we present the unveiling of an open-source software package designed to facili... more In this discourse, we present the unveiling of an open-source software package designed to facilitate engagement with the atmospheric model, Aeolus 2.0. This particular iteration stands as a self-contained model of intermediate complexity. The model's dynamical core is underpinned by a multi-layer pseudo-spectral moist-convective Thermal Rotating Shallow Water (mcTRSW) model. The pseudo-spectral problem-solving tasks are handled by the Dedalus algorithm, acknowledged for its spin-weighted spherical harmonics. The model captures the temporal and spatial evolution of vertically integrated potential temperature, thickness, water vapour, precipitation, and the intricate influence of bottom topography. It comprehensively characterizes velocity fields in both the lower and upper troposphere, employing resolutions spanning a spectrum from the smooth to the coarse, enabling the exploration of a wide range of dynamic phenomena with varying levels of detail and precision.
We study the impact of recent global warming on extreme climatic events in Central Asia (CA) for ... more We study the impact of recent global warming on extreme climatic events in Central Asia (CA) for 1901-2019 by comparing the composite representation of the observational climate with a hypothetical counterfactual one that does not include the long-term global warming trend. The counterfactual climate data are produced based on a simple detrending approach, using the global mean temperature (GMT) as the independent variable and removing the longterm trends from the climate variables of the observational data. This trend elimination is independent of causality, and the day-today variability in the counterfactual climate remains preserved. The analysis done in the paper shows that the increase in frequency and magnitude of extreme temperature and precipitation events can be attributed to global warming. Specifically, the probability of experiencing a +7 K temperature anomaly event in CA increases by up to a factor of seven in some areas due to global warming. The analysis reveals a significant increase in heatwave occurrences in Central Asia, with the observational climate dataset GSWP3-W5E5 (later called also factual) showing more frequent and prolonged extreme heat events than hypothetical scenarios without global warming. This trend, evident in the disparity between factual and counterfactual data, underscores the critical impact of recent climatic changes on weather patterns, highlighting the urgent need for robust adaptation and mitigation strategies. Additionally, using the self-calibrated Palmer drought severity index (scPDSI), the sensitivity of dry and wet events to the coupled precipitation and temperature changes is analyzed. The areas under dry and wet conditions are enhanced under the observational climate compared to a counterfactual scenario, especially over the largest deserts in CA. The expansion of the dry regions aligns well with the pattern of desert development observed in CA in recent decades. Keywords Climate change • Central Asia • Drought • Extreme events • Heatwaves B Bijan Fallah
By means of a new multilayer pseudo-spectral moist-convective thermal rotating shallow-water (mcT... more By means of a new multilayer pseudo-spectral moist-convective thermal rotating shallow-water (mcTRSW) model in a full sphere, we present a possible equatorial adjustment beyond Gill’s mechanism for the genesis and dynamics of the Madden–Julian oscillation (MJO). According to this theory, an eastward-propagating MJO-like structure can be generated in a self-sustained and self-propelled manner due to nonlinear relaxation (adjustment) of a large-scale positive buoyancy anomaly, depressed anomaly, or a combination of these, as soon as this anomaly reaches a critical threshold in the presence of moist convection at the Equator. This MJO-like episode possesses a convectively coupled “hybrid structure” that consists of a “quasi-equatorial modon” with an enhanced vortex pair and a convectively coupled baroclinic Kelvin wave (BKW), with greater phase speed than that of dipolar structure on an intraseasonal time-scale. Interaction of the BKW, after circumnavigating the entire Equator, with a new large-scale buoyancy anomaly may contribute to excitation of a recurrent generation of the next cycle of MJO-like structure. Overall, the generated “hybrid structure” captures a few of the crudest features of the MJO, includingits quadrupolar structure, convective activity, condensation patterns, vorticity field, phase speed, and westerly and easterly inflows in the lower and upper troposphere. Although moisture-fed convection is a necessary condition for the “hybrid structure” to be excited and maintained in the proposed theory in this study, it is fundamentally different from moisture-mode theories, because the barotropic equatorial modon and BKW also exist in “dry” environments, while there are no similar “dry” dynamical basic structures in moisture-mode theories. The proposed theory can therefore be a possible mechanism to explain the genesis and backbone structure of the MJO and to converge some theories that previously seemed divergent (DOI:10.1002/qj.4388).
This study investigates the adjustment of large‐scale localized buoyancy anomalies in mid‐latitud... more This study investigates the adjustment of large‐scale localized buoyancy anomalies in mid‐latitude regions and the nonlinear evolution of associated condensation patterns in both adiabatic and moist‐convective environments. This investigation is carried out utilizing the two‐layer idealized moist‐convective thermal rotating shallow water (mcTRSW) model. Our investigation reveals that the presence of a circular positive potential temperature anomaly in the lower layer initiates an anticyclonic high‐pressure rotation, accompanied by a negative buoyancy anomaly in the upper layer, resulting in an anisotropic northeast–southwest tilted circulation of heat flux. The evolution of eddy heat fluxes, such as poleward heat flux, energy, and meridional elongation of the buoyancy field, heavily depends on the perturbation's strength, size, and vertical structure. The heatwave initiates atmospheric instability, leading to precipitation systems such as rain bands and asymmetric latent heat re...
By means of a new multilayer pseudo-spectral moist-convective thermal rotating shallow-water (mcT... more By means of a new multilayer pseudo-spectral moist-convective thermal rotating shallow-water (mcTRSW) model in a full sphere, we present a possible equatorial adjustment beyond Gill’s mechanism for the genesis and dynamics of the Madden–Julian oscillation (MJO). According to this theory, an eastward-propagating MJO-like structure can be generated in a self-sustained and self-propelled manner due to nonlinear relaxation (adjustment) of a large-scale positive buoyancy anomaly, depressed anomaly, or a combination of these, as soon as this anomaly reaches a critical threshold in the presence of moist convection at the Equator. This MJO-like episode possesses a convectively coupled “hybrid structure” that consists of a “quasi-equatorial modon” with an enhanced vortex pair and a convectively coupled baroclinic Kelvin wave (BKW), with greater phase speed than that of dipolar structure on an intraseasonal time-scale. Interaction of the BKW, after circumnavigating the entire Equator, with a ...
Quarterly Journal of the Royal Meteorological Society
By means of a new multilayer pseudo‐spectral moist‐convective thermal rotating shallow‐water (mcT... more By means of a new multilayer pseudo‐spectral moist‐convective thermal rotating shallow‐water (mcTRSW) model in a full sphere, we present a possible equatorial adjustment beyond Gill's mechanism for the genesis and dynamics of the Madden–Julian oscillation (MJO). According to this theory, an eastward‐propagating MJO‐like structure can be generated in a self‐sustained and self‐propelled manner due to nonlinear relaxation (adjustment) of a large‐scale positive buoyancy anomaly, depressed anomaly, or a combination of these, as soon as this anomaly reaches a critical threshold in the presence of moist convection at the Equator. This MJO‐like episode possesses a convectively coupled “hybrid structure” that consists of a “quasi‐equatorial modon” with an enhanced vortex pair and a convectively coupled baroclinic Kelvin wave (BKW), with greater phase speed than that of dipolar structure on an intraseasonal time‐scale. Interaction of the BKW, after circumnavigating the entire Equator, wit...
A detailed investigation of linear instabilities of double-eyewall hurricane-like vortices with d... more A detailed investigation of linear instabilities of double-eyewall hurricane-like vortices with double maxima ("walls") of azimuthal velocity and vorticity around the central minimum ("eye") and of their nonlinear saturation is carried out in the framework of the moist-convective rotating shallow water model. It is shown that developing barotropic instability leads to inward displacement and gradual disappearance of the inner wall, and to formation of a nontrivial tripolar quasi-stationary structure, provided the second, outer, wall of the initial vortex is high enough. The effects of moist convection lead to enhancement of the outer wall. In comparison, under the influence of the same instability, vortices with an inner wall stronger than the outer one evolve towards monopolar single-eyewall structures.
Abstract The Aurignacian occurred in the middle of the Last Glacial Period, in which climate unde... more Abstract The Aurignacian occurred in the middle of the Last Glacial Period, in which climate underwent major changes on millennial time scales, highlighted by the Greenland interstadial and stadial periods. Here we investigate how climate change influenced the Aurignacian human dispersal in Europe and search for answers to several highly-debated questions in the Archaeology and Paleoanthropology. We use a global climate model to simulate the prototypical stadial and interstadial climate conditions and develop a human-existence potential (HEP) model to compute the probability of human existence by combining the climate data with archaeological site data. Using the HEP model, we reconstruct the patterns of human-existence probability and provide a pan-European overview of the Aurignacian human dispersal. The model results suggest that climate change significantly influences human dispersal, but there is evidence of human adaptation to climate. The Aurignacian dispersal is likely achieved in alternating modes of expansion and contraction. In comparison to interstadial times, human-existence probability in stadial times is largely reduced, but hot-spots exist in the climate shadows of large topographic features.
We employ a high-resolution Köppen climate classification dataset to examine shifts in Tundra zon... more We employ a high-resolution Köppen climate classification dataset to examine shifts in Tundra zones within the Alps and Asia. Our analysis shows substantial reductions in Tundra areas by the mid-21st century under different Shared. Socioeconomic pathways (SSP1-2.6, SSP3-7.0, SSP5-8.5). Tundra zones in the Alps and the Tibetan Plateau are crucial for their unique climates and role as water reservoirs. Characterized by short, mild summers and long, severe winters, these zones are vital for the glaciers and perennial snow. The projected climate instability may significantly reduce alpine snow cover by mid-century with irreversible consequences. A 2 C temperature increase from the 1981-2010 baseline could eliminate the Tundra climate in the Alps and reduce it by over 70% in Asia. This is particularly concerning given that rivers from the Tibetan Plateau sustain nearly 40% of the global population.
A detailed investigation of linear instabilities of double-eyewall hurricane-like vortices with d... more A detailed investigation of linear instabilities of double-eyewall hurricane-like vortices with double maxima (“walls”) of azimuthal velocity and vorticity around the central minimum (“eye”) and of their nonlinear saturation is carried out in the framework of the moist-convective rotating shallow water model. It is shown that developing barotropic instability leads to inward displacement and gradual disappearance of the inner wall and to the formation of a nontrivial tripolar quasi-stationary structure, provided the second, outer, wall of the initial vortex is high enough. The effects of moist convection lead to the enhancement of the outer wall. In comparison, under the influence of the same instability, vortices with an inner wall stronger than the outer one evolve toward monopolar single-eyewall structures.
Central Asia (CA) is among the world's most vulnerable regions to climate change. Increasing anth... more Central Asia (CA) is among the world's most vulnerable regions to climate change. Increasing anthropogenic greenhouse gas concentrations (GHGs) are the primary forcing of the current and future climate system for the time scale of a century. By analysing observation datasets, we show that a warming of 1.2 C led to a decrease of 20% in snow-depth CA during the last 70 years, especially over the mountains. In recent decades, longer summer times and fewer icing days (more than 20 daysÁyear −1) have exposed unprecedented shock to CA's climate system's components. Furthermore, we analyse 442 model ...
In this discourse, we present the unveiling of an open-source software package designed to facili... more In this discourse, we present the unveiling of an open-source software package designed to facilitate engagement with the atmospheric model, Aeolus 2.0. This particular iteration stands as a self-contained model of intermediate complexity. The model's dynamical core is underpinned by a multi-layer pseudo-spectral moist-convective Thermal Rotating Shallow Water (mcTRSW) model. The pseudo-spectral problem-solving tasks are handled by the Dedalus algorithm, acknowledged for its spin-weighted spherical harmonics. The model captures the temporal and spatial evolution of vertically integrated potential temperature, thickness, water vapour, precipitation, and the intricate influence of bottom topography. It comprehensively characterizes velocity fields in both the lower and upper troposphere, employing resolutions spanning a spectrum from the smooth to the coarse, enabling the exploration of a wide range of dynamic phenomena with varying levels of detail and precision.
We study the impact of recent global warming on extreme climatic events in Central Asia (CA) for ... more We study the impact of recent global warming on extreme climatic events in Central Asia (CA) for 1901-2019 by comparing the composite representation of the observational climate with a hypothetical counterfactual one that does not include the long-term global warming trend. The counterfactual climate data are produced based on a simple detrending approach, using the global mean temperature (GMT) as the independent variable and removing the longterm trends from the climate variables of the observational data. This trend elimination is independent of causality, and the day-today variability in the counterfactual climate remains preserved. The analysis done in the paper shows that the increase in frequency and magnitude of extreme temperature and precipitation events can be attributed to global warming. Specifically, the probability of experiencing a +7 K temperature anomaly event in CA increases by up to a factor of seven in some areas due to global warming. The analysis reveals a significant increase in heatwave occurrences in Central Asia, with the observational climate dataset GSWP3-W5E5 (later called also factual) showing more frequent and prolonged extreme heat events than hypothetical scenarios without global warming. This trend, evident in the disparity between factual and counterfactual data, underscores the critical impact of recent climatic changes on weather patterns, highlighting the urgent need for robust adaptation and mitigation strategies. Additionally, using the self-calibrated Palmer drought severity index (scPDSI), the sensitivity of dry and wet events to the coupled precipitation and temperature changes is analyzed. The areas under dry and wet conditions are enhanced under the observational climate compared to a counterfactual scenario, especially over the largest deserts in CA. The expansion of the dry regions aligns well with the pattern of desert development observed in CA in recent decades. Keywords Climate change • Central Asia • Drought • Extreme events • Heatwaves B Bijan Fallah
By means of a new multilayer pseudo-spectral moist-convective thermal rotating shallow-water (mcT... more By means of a new multilayer pseudo-spectral moist-convective thermal rotating shallow-water (mcTRSW) model in a full sphere, we present a possible equatorial adjustment beyond Gill’s mechanism for the genesis and dynamics of the Madden–Julian oscillation (MJO). According to this theory, an eastward-propagating MJO-like structure can be generated in a self-sustained and self-propelled manner due to nonlinear relaxation (adjustment) of a large-scale positive buoyancy anomaly, depressed anomaly, or a combination of these, as soon as this anomaly reaches a critical threshold in the presence of moist convection at the Equator. This MJO-like episode possesses a convectively coupled “hybrid structure” that consists of a “quasi-equatorial modon” with an enhanced vortex pair and a convectively coupled baroclinic Kelvin wave (BKW), with greater phase speed than that of dipolar structure on an intraseasonal time-scale. Interaction of the BKW, after circumnavigating the entire Equator, with a new large-scale buoyancy anomaly may contribute to excitation of a recurrent generation of the next cycle of MJO-like structure. Overall, the generated “hybrid structure” captures a few of the crudest features of the MJO, includingits quadrupolar structure, convective activity, condensation patterns, vorticity field, phase speed, and westerly and easterly inflows in the lower and upper troposphere. Although moisture-fed convection is a necessary condition for the “hybrid structure” to be excited and maintained in the proposed theory in this study, it is fundamentally different from moisture-mode theories, because the barotropic equatorial modon and BKW also exist in “dry” environments, while there are no similar “dry” dynamical basic structures in moisture-mode theories. The proposed theory can therefore be a possible mechanism to explain the genesis and backbone structure of the MJO and to converge some theories that previously seemed divergent (DOI:10.1002/qj.4388).
This study investigates the adjustment of large‐scale localized buoyancy anomalies in mid‐latitud... more This study investigates the adjustment of large‐scale localized buoyancy anomalies in mid‐latitude regions and the nonlinear evolution of associated condensation patterns in both adiabatic and moist‐convective environments. This investigation is carried out utilizing the two‐layer idealized moist‐convective thermal rotating shallow water (mcTRSW) model. Our investigation reveals that the presence of a circular positive potential temperature anomaly in the lower layer initiates an anticyclonic high‐pressure rotation, accompanied by a negative buoyancy anomaly in the upper layer, resulting in an anisotropic northeast–southwest tilted circulation of heat flux. The evolution of eddy heat fluxes, such as poleward heat flux, energy, and meridional elongation of the buoyancy field, heavily depends on the perturbation's strength, size, and vertical structure. The heatwave initiates atmospheric instability, leading to precipitation systems such as rain bands and asymmetric latent heat re...
By means of a new multilayer pseudo-spectral moist-convective thermal rotating shallow-water (mcT... more By means of a new multilayer pseudo-spectral moist-convective thermal rotating shallow-water (mcTRSW) model in a full sphere, we present a possible equatorial adjustment beyond Gill’s mechanism for the genesis and dynamics of the Madden–Julian oscillation (MJO). According to this theory, an eastward-propagating MJO-like structure can be generated in a self-sustained and self-propelled manner due to nonlinear relaxation (adjustment) of a large-scale positive buoyancy anomaly, depressed anomaly, or a combination of these, as soon as this anomaly reaches a critical threshold in the presence of moist convection at the Equator. This MJO-like episode possesses a convectively coupled “hybrid structure” that consists of a “quasi-equatorial modon” with an enhanced vortex pair and a convectively coupled baroclinic Kelvin wave (BKW), with greater phase speed than that of dipolar structure on an intraseasonal time-scale. Interaction of the BKW, after circumnavigating the entire Equator, with a ...
Quarterly Journal of the Royal Meteorological Society
By means of a new multilayer pseudo‐spectral moist‐convective thermal rotating shallow‐water (mcT... more By means of a new multilayer pseudo‐spectral moist‐convective thermal rotating shallow‐water (mcTRSW) model in a full sphere, we present a possible equatorial adjustment beyond Gill's mechanism for the genesis and dynamics of the Madden–Julian oscillation (MJO). According to this theory, an eastward‐propagating MJO‐like structure can be generated in a self‐sustained and self‐propelled manner due to nonlinear relaxation (adjustment) of a large‐scale positive buoyancy anomaly, depressed anomaly, or a combination of these, as soon as this anomaly reaches a critical threshold in the presence of moist convection at the Equator. This MJO‐like episode possesses a convectively coupled “hybrid structure” that consists of a “quasi‐equatorial modon” with an enhanced vortex pair and a convectively coupled baroclinic Kelvin wave (BKW), with greater phase speed than that of dipolar structure on an intraseasonal time‐scale. Interaction of the BKW, after circumnavigating the entire Equator, wit...
A detailed investigation of linear instabilities of double-eyewall hurricane-like vortices with d... more A detailed investigation of linear instabilities of double-eyewall hurricane-like vortices with double maxima ("walls") of azimuthal velocity and vorticity around the central minimum ("eye") and of their nonlinear saturation is carried out in the framework of the moist-convective rotating shallow water model. It is shown that developing barotropic instability leads to inward displacement and gradual disappearance of the inner wall, and to formation of a nontrivial tripolar quasi-stationary structure, provided the second, outer, wall of the initial vortex is high enough. The effects of moist convection lead to enhancement of the outer wall. In comparison, under the influence of the same instability, vortices with an inner wall stronger than the outer one evolve towards monopolar single-eyewall structures.
Abstract The Aurignacian occurred in the middle of the Last Glacial Period, in which climate unde... more Abstract The Aurignacian occurred in the middle of the Last Glacial Period, in which climate underwent major changes on millennial time scales, highlighted by the Greenland interstadial and stadial periods. Here we investigate how climate change influenced the Aurignacian human dispersal in Europe and search for answers to several highly-debated questions in the Archaeology and Paleoanthropology. We use a global climate model to simulate the prototypical stadial and interstadial climate conditions and develop a human-existence potential (HEP) model to compute the probability of human existence by combining the climate data with archaeological site data. Using the HEP model, we reconstruct the patterns of human-existence probability and provide a pan-European overview of the Aurignacian human dispersal. The model results suggest that climate change significantly influences human dispersal, but there is evidence of human adaptation to climate. The Aurignacian dispersal is likely achieved in alternating modes of expansion and contraction. In comparison to interstadial times, human-existence probability in stadial times is largely reduced, but hot-spots exist in the climate shadows of large topographic features.
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Papers by Masoud Rostami