The Tropospheric Response to Tropical and Subtropical Zonally Asymmetric Torques: Analytical and Idealized Numerical Model Results

2012 ◽  
Vol 69 (1) ◽  
pp. 214-235 ◽  
Author(s):  
Tiffany A. Shaw ◽  
William R. Boos
Keyword(s):  
Temperature Gradient ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Large Scale ◽  
Critical Line ◽  
Circulation Model ◽  
General Circulation Models ◽  
Kelvin Wave ◽  
Meridional Temperature Gradient ◽  
Poleward Shift

Abstract The tropospheric response to prescribed tropical and subtropical zonally asymmetric torques, which can be considered as idealizations of vertical momentum transfers by orographic gravity waves or convection, is investigated. The linear analytical Gill model response to westward upper-tropospheric torques is compared to the response to a midtropospheric heating, which is a familiar point of reference. The response to an equatorial torque projects onto a Kelvin wave response to the east that is of opposite sign to the response to the east of the heating at upper levels. In contrast, the torque and heating both produce Rossby gyres of the same sign to the west of the forcing and the zonal-mean streamfunction responses are identical. When the forcings are shifted into the Northern Hemisphere, the streamfunction responses have opposite signs: there is upwelling in the Southern (Northern) Hemisphere in response to the torque (heating). The nonlinear response to westward torques was explored in idealized general circulation model experiments. In the absence of a large-scale meridional temperature gradient, the response to an equatorial torque was confined to the tropics and was qualitatively similar to the linear solutions. When the torque was moved into the subtropics, the vorticity budget response was similar to a downward control–type balance in the zonal mean. In the presence of a meridional temperature gradient, the response to an equatorial torque involved a poleward shift of the midlatitude tropospheric jet and Ferrel cell. The response in midlatitudes was associated with a poleward shift of the regions of horizontal eddy momentum flux convergence, which coincided with a shift in the upper-tropospheric critical line for baroclinic waves. The shift in the critical line was caused (in part) by the zonal wind response to the prescribed torque, suggesting a possible cause of the response in midlatitudes. Overall, this hierarchy of analytical and numerical results highlights robust aspects of the response to tropical and subtropical zonally asymmetric torques and represents the first step toward understanding the response in fully comprehensive general circulation models.

scholarly journals Summer Westerly Jet in Northern Hemisphere during the Mid-Holocene: A Multi-Model Study

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1193
Author(s):  
Chuchu Xu ◽  
Mi Yan ◽  
Liang Ning ◽  
Jian Liu
Keyword(s):  
Temperature Gradient ◽  
Northern Hemisphere ◽  
Hadley Cell ◽  
Dynamic Processes ◽  
Jet Stream ◽  
Meridional Temperature Gradient ◽  
The North ◽  
Westerly Jet ◽  
Poleward Shift ◽  
Thermodynamic Processes

The upper-level jet stream, a narrow band of maximum wind speed in the mid-latitude westerlies, exerts a considerable influence on the global climate by modulating the transport and distribution of momentum, heat and moisture. In this study by using four high-resolution models in the Paleoclimate Modelling Intercomparison Project phase 3, the changes of position and intensity of the northern hemisphere westerly jet at 200 hPa in summer during the mid-Holocene (MH), as well as the related mechanisms, are investigated. The four models show similar performance on the westerly jet. At the hemispheric scale, the simulated westerly jet has a poleward shift during the MH compared to the preindustrial period. The warming in arctic and cooling in the tropics during the MH are caused by the orbital changes of the earth and the precipitation changes, and it could lead to the weakened meridional temperature gradient and pressure gradient, which might account for the poleward shift of the westerly jet from the thermodynamic perspective. From the dynamic perspective, two maximum centers of eddy kinetic energy are simulated over the North Pacific and North Atlantic with the north deviation, which could cause the northward movement of the westerly jet. The weakening of the jet stream is associated with the change of the Hadley cell and the meridional temperature gradient. The largest weakening is over the Pacific Ocean where both the dynamic and the thermodynamic processes have weakening effects. The smallest weakening is over the Atlantic Ocean, and it is induced by the offset effects of dynamic processes and thermodynamic processes. The weakening over the Eurasia is mainly caused by the dynamic processes.

scholarly journals Evaluation of a unique approach to high-resolution climate modeling using the Model for Prediction Across Scales – Atmosphere (MPAS-A) version 5.1

2019 ◽  
Vol 12 (8) ◽  
pp. 3725-3743 ◽  
Author(s):  
Allison C. Michaelis ◽  
Gary M. Lackmann ◽  
Walter A. Robinson
Keyword(s):  
Climate Change ◽  
High Resolution ◽  
Sea Ice ◽  
Northern Hemisphere ◽  
General Circulation ◽  
Large Scale ◽  
Southern Oscillation ◽  
Spatial Scales ◽  
Coupled Model ◽  
General Circulation Models

Abstract. We present multi-seasonal simulations representative of present-day and future environments using the global Model for Prediction Across Scales – Atmosphere (MPAS-A) version 5.1 with high resolution (15 km) throughout the Northern Hemisphere. We select 10 simulation years with varying phases of El Niño–Southern Oscillation (ENSO) and integrate each for 14.5 months. We use analyzed sea surface temperature (SST) patterns for present-day simulations. For the future climate simulations, we alter present-day SSTs by applying monthly-averaged temperature changes derived from a 20-member ensemble of Coupled Model Intercomparison Project phase 5 (CMIP5) general circulation models (GCMs) following the Representative Concentration Pathway (RCP) 8.5 emissions scenario. Daily sea ice fields, obtained from the monthly-averaged CMIP5 ensemble mean sea ice, are used for present-day and future simulations. The present-day simulations provide a reasonable reproduction of large-scale atmospheric features in the Northern Hemisphere such as the wintertime midlatitude storm tracks, upper-tropospheric jets, and maritime sea-level pressure features as well as annual precipitation patterns across the tropics. The simulations also adequately represent tropical cyclone (TC) characteristics such as strength, spatial distribution, and seasonal cycles for most Northern Hemisphere basins. These results demonstrate the applicability of these model simulations for future studies examining climate change effects on various Northern Hemisphere phenomena, and, more generally, the utility of MPAS-A for studying climate change at spatial scales generally unachievable in GCMs.

scholarly journals Influence of the SST Rise on Baroclinic Instability Wave Activity under an Aquaplanet Condition

2009 ◽  
Vol 66 (8) ◽  
pp. 2272-2287 ◽  
Author(s):  
Chihiro Kodama ◽  
Toshiki Iwasaki
Keyword(s):  
Global Warming ◽  
Temperature Gradient ◽  
Wave Energy ◽  
General Circulation ◽  
Baroclinic Instability ◽  
Lower Troposphere ◽  
Wave Activity ◽  
Instability Wave ◽  
Meridional Temperature Gradient ◽  
Poleward Shift

Abstract The influence of the sea surface temperature (SST) rise on extratropical baroclinic instability wave activity is investigated using an aquaplanet general circulation model (GCM). Two types of runs were performed: the High+3 run, in which the SST is increased by 3 K only at high latitudes, and the All+3 run, in which the SST is increased uniformly by 3 K all over the globe. These SST rises were intended to reproduce essential changes of the surface air temperature due to global warming. Wave activity changes are analyzed and discussed from the viewpoint of the energetics. In the High+3 run, midlatitude meridional temperature gradient is decreased in the lower troposphere and the wave energy is suppressed in the extratropics. In the All+3 run, although the large tropical latent heat release greatly enhances the midlatitude meridional temperature gradient in the upper troposphere, global mean wave energy does not change significantly. These results suggest that the low-level baroclinicity is much more important for baroclinic instability wave activity than upper-level baroclinicity. A poleward shift of wave energy, seen in global warming simulations, is evident in the All+3 run. Wave energy generation analysis suggests that the poleward shift of wave activity may be caused by the enhanced and poleward-shifted baroclinicity in the higher latitudes and the increased static stability in the lower latitudes. Poleward expansion of the high-baroclinicity region is still an open question.

Estimating structural and parametric uncertainties in the simulated early Eocene surface warming

2020 ◽  
Author(s):  
Sebastian Steinig ◽  
Fran J. Bragg ◽  
Peter J. Irvine ◽  
Daniel J. Lunt ◽  
Paul J. Valdes
Keyword(s):  
Temperature Gradient ◽  
Boundary Conditions ◽  
Greenhouse Gas ◽  
General Circulation ◽  
Parametric Uncertainty ◽  
General Circulation Models ◽  
Parametric Uncertainties ◽  
Early Eocene ◽  
Meridional Temperature Gradient ◽  
Surface Warming

<p>Simulating the proxy-derived surface warming and reduced meridional temperature gradient of the early Eocene greenhouse climate still represents a challenge for most atmosphere-ocean general circulation models. A profound understanding of uncertainties associated with the respective model results is thereby essential to reliably identify any similarities or misfits to the proxy record. Besides incomplete knowledge of past greenhouse gas concentrations and other boundary conditions, structural and parametric uncertainties are the main factors that determine our confidence in paleoclimate simulation results.</p><p>The recent publication of coordinated model experiments that apply identical paleogeographic boundary conditions for key time periods of the early Eocene (DeepMIP) allows a systematic analysis of inter-model differences and therefore of structural uncertainties in the simulated surface warming. Here we additionally explore the parametric uncertainty of the early Eocene climatic optimum (EECO) surface warming within one DeepMIP model. For this we performed perturbed parameter ensemble (PPE) simulations with HadCM3B at different atmospheric CO<sub>2</sub> concentrations following the DeepMIP protocol. Twenty-one parameter sets based on changes in six atmospheric parameters, a sea-ice parameter and the ocean background diffusivity were branched off from the respective DeepMIP control simulations and integrated for a further 1500 model years. The selected parameter sets are based on previous results demonstrating their ability to simulate a pre-industrial global-mean surface temperature within ±2 °C of the standard configuration.</p><p>Preliminary results indicate a large spread of the simulated low-latitude surface warming in the PPE and therefore significant changes of the large-scale meridional temperature gradient for the EECO. Some ensemble members develop numerical instabilities at CO<sub>2</sub> concentrations of 840 ppmv and above, most likely in consequence of high temperatures in the tropical troposphere. We further compare the magnitude of the parametric uncertainty of the HadCM3B perturbation experiments with the structural differences found in the DeepMIP multi-model ensemble and explore the sensitivity of the results to the strength of the applied greenhouse gas forcing. Model skill of the PPE members is tested against the most recent DeepMIP compilations of marine and terrestrial proxy temperatures.</p>

scholarly journals Storm Track Shifts under Climate Change: What Can Be Learned from Large-Scale Dry Dynamics

2013 ◽  
Vol 26 (24) ◽  
pp. 9923-9930 ◽  
Author(s):  
Cheikh Mbengue ◽  
Tapio Schneider
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Large Scale ◽  
Storm Track ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Phase Changes ◽  
Storm Tracks ◽  
Convective Stability ◽  
Poleward Shift

Abstract Earth’s storm tracks are instrumental for transporting heat, momentum, and moisture and thus strongly influence the surface climate. Climate models, supported by a growing body of observational data, have demonstrated that storm tracks shift poleward as the climate warms. But the dynamical mechanisms responsible for this shift remain unclear. To isolate what portion of the storm track shift may be accounted for by large-scale dry dynamics alone, disregarding the latent heat released in phase changes of water, this study investigates the storm track shift under various kinds of climate change in an idealized dry general circulation model (GCM) with an adjustable but constant convective stability. It is found that increasing the mean surface temperature or the convective stability leads to poleward shifts of storm tracks, even if the convective stability is increased only in a narrow band around the equator. Under warming and convective stability changes roughly corresponding to a doubling of CO2 concentrations from a present-day Earthlike climate, storm tracks shift about 0.8° poleward, somewhat less than but in qualitative agreement with studies using moist GCMs. About 63% (0.5°) of the poleward shift is shown to be caused by tropical convective stability variations. This demonstrates that tropical processes alone (the increased dry static stability of a warmer moist adiabat) can account for part of the poleward shift of storm tracks under global warming. This poleward shift generally occurs in tandem with a poleward expansion of the Hadley circulation; however, the Hadley circulation expansion does not always parallel the storm track shift.

scholarly journals EPIC simulations of Neptune’s dark spots using an active cloud microphysical model

2020 ◽  
Vol 496 (4) ◽  
pp. 4760-4768
Author(s):  
Nathan Hadland ◽  
Ramanakumar Sankar ◽  
Raymond Paul LeBeau ◽  
Csaba Palotai
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Large Scale ◽  
Dynamic Properties ◽  
Circulation Model ◽  
Cloud Microphysics ◽  
Cloud Formation ◽  
Explicit Calculation ◽  
Dark Spot ◽  
Vapour Density

ABSTRACT The Great Dark Spot (GDS-89) observed by Voyager 2 was the first of several large-scale vortices observed on Neptune, the most recent of which was observed in 2018 in the Northern hemisphere (NDS-2018). Ongoing observations of these features are constraining cloud formation, drift, shape oscillations, and other dynamic properties. In order to effectively model these characteristics, an explicit calculation of methane cloud microphysics is needed. Using an updated version of the Explicit Planetary Isentropic Coordinate General Circulation Model (EPIC GCM) and its active cloud microphysics module to account for the condensation of methane, we investigate the evolution of large-scale vortices on Neptune. We model the effect of methane deep abundance and cloud formation on vortex stability and dynamics. In our simulations, the vortex shows a sharp contrast in methane vapour density inside compared to outside the vortex. Methane vapour column density is analogous to optical depth and provides a more consistent tracer to track the vortex, so we use that variable over potential vorticity. We match the meridional drift rate of the GDS and gain an initial insight into the evolution of vortices in the Northern hemisphere, such as the NDS-2018.

The MJO and Convectively Coupled Waves in a Coarse-Resolution GCM with a Simple Multicloud Parameterization

2011 ◽  
Vol 68 (2) ◽  
pp. 240-264 ◽  
Author(s):  
Boualem Khouider ◽  
Amik St-Cyr ◽  
Andrew J. Majda ◽  
Joseph Tribbia
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Deep Convection ◽  
General Circulation Models ◽  
Moisture Gradient ◽  
Kelvin Wave ◽  
The Third ◽  
Coarse Resolution ◽  
Convectively Coupled Waves ◽  
Zonal Wavenumber

Abstract The adequate representation of the dominant intraseasonal and synoptic-scale variability in the tropics, characterized by the Madden–Julian oscillation (MJO) and convectively coupled waves, is still problematic in current operational general circulation models (GCMs). Here results are presented using the next-generation NCAR GCM—the High-Order Methods Modeling Environment (HOMME)—as a dry dynamical core at a coarse resolution of about 167 km, coupled to a simple multicloud parameterization. The coupling is performed through a judicious choice of heating vertical profiles for the three cloud types—congestus, deep, and stratiform—that characterize organized tropical convection. Important control parameters that affect the types of waves that emerge are the background vertical gradient of the moisture and the stratiform fraction in the multicloud parameterization, which set the strength of large-scale moisture convergence and unsaturated downdrafts in the wake of deep convection, respectively. Three numerical simulations using different moisture gradients and different stratiform fractions are considered. The first experiment uses a large moisture gradient and a small stratiform fraction and provides an MJO-like example. It results in an intraseasonal oscillation of zonal wavenumber 2, moving eastward at a constant speed of roughly 5 m s−1. The second uses a weaker background moisture gradient and a large stratiform fraction and yields convectively coupled Rossby, Kelvin, and two-day waves, embedded in and interacting with each other; and the third experiment combines the small stratiform fraction and the weak background moisture gradient to yield a planetary-scale (wavenumber 1) second baroclinic Kelvin wave. While the first two experiments provide two benchmark examples that reproduce several key features of the observational record, the third is more of a demonstration of a bad MJO model solution that exhibits very unrealistic features.

scholarly journals Impact of the Warming Pattern on Global Energetics

2012 ◽  
Vol 25 (15) ◽  
pp. 5223-5240 ◽  
Author(s):  
Daniel Hernández-Deckers ◽  
Jin-Song von Storch
Keyword(s):  
Temperature Gradient ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Static Stability ◽  
Meridional Temperature Gradient ◽  
Surface Warming ◽  
Warming Pattern ◽  
Atmospheric Energetics ◽  
The Mean

Abstract The warming pattern due to higher greenhouse gas concentrations is expected to affect the global atmospheric energetics mainly via changes in the (i) meridional temperature gradient and (ii) mean static stability. Changes in surface meridional temperature gradients have been previously regarded as the determining feature for the energetics response, but recent studies suggest that changes in mean static stability may be more relevant than previously thought. This study aims to determine the relative importance of these two effects by comparing the energetics responses due to different warming patterns using a fully coupled atmosphere–ocean general circulation model. By means of an additional diabatic forcing, experiments with different warming patterns are obtained: one with a 2xCO2-like pattern that validates the method, one with only the tropical upper-tropospheric warming, and one with only the high-latitude surface warming. The study’s findings suggest that the dominant aspect of the warming pattern that alters the global atmospheric energetics is not its associated meridional temperature gradient changes, but the mean static stability changes. The tropical upper warming weakens the energetics by increasing the mean static stability, whereas the surface warming strengthens it by reducing the mean static stability. The combined 2xCO2-like response is dominated by the tropical upper-tropospheric warming effect, hence the weaker energetic activity. Eddy kinetic energy changes consistently, but the two opposite responses nearly cancel each other in the 2xCO2 case. Therefore, estimates of future changes in storminess may be particularly sensitive to the relative magnitude of the main features of the simulated warming pattern.

scholarly journals The sensitivity of the large-scale atmosphere circulation to changes in surface temperature gradients in the Northern Hemisphere

2017 ◽  
Author(s):  
Sonja Molnos ◽  
Stefan Petri ◽  
Jascha Lehmann ◽  
Erik Peukert ◽  
Dim Coumou
Keyword(s):  
Temperature Gradient ◽  
Surface Temperature ◽  
Northern Hemisphere ◽  
Large Scale ◽  
Planetary Waves ◽  
Hadley Cell ◽  
Temperature Fields ◽  
Storm Tracks ◽  
Meridional Temperature Gradient ◽  
Jet Streams

Abstract. Climate and weather conditions in the mid-latitudes are strongly driven by the large-scale atmosphere circulation. Observational data indicates that important components of the large-scale circulation have changed in recent decades including the strength of the Hadley cell, jet streams, storm tracks and planetary waves. Associated impacts cover a broad range, including changes in the frequency and nature of weather extremes and shifts of fertile habitats with implications for biodiversity and agriculture. Dynamical theories have been proposed that link the shift of the poleward edge of the Northern Hadley cell to changes in the meridional temperature gradient. Moreover, model simulations have been carried out to analyse the cause of observed and projected changes in the large-scale atmosphere circulation. However, the question of the underlying drivers and particularly the possible role of global warming is still debated. Here, we use a statistical-dynamical atmosphere model (SDAM) to analyse the sensitivity of the Northern Hemisphere Hadley cell, storm tracks, jet streams and planetary waves to changes in temperature fields by systematically altering the zonal and meridional temperature gradient as well as the global mean surface temperature.

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