A Model Investigation of Aerosol-Induced Changes in Tropical Circulation

2011 ◽  
Vol 24 (19) ◽  
pp. 5125-5133 ◽  
Author(s):  
Yi Ming ◽  
V. Ramaswamy
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Hydrological Response ◽  
Moist Static Energy ◽  
Tropical Circulation ◽  
Anthropogenic Aerosols ◽  
Model Aerosol ◽  
Static Energy

This study investigates how anthropogenic aerosols, alone or in conjunction with radiatively active gases, affect the tropical circulation with an atmosphere/mixed layer–ocean general circulation model. Aerosol-induced cooling gives rise to a substantial increase in the overall strength of the tropical circulation, a robust outcome consistent with a thermodynamical scaling argument. Owing to the interhemispheric asymmetry in aerosol forcing, the zonal-mean (Hadley) and zonally asymmetrical components of the tropical circulation respond differently. The Hadley circulation weakens in the Northern Hemisphere but strengthens in the Southern Hemisphere. The resulting northward cross-equatorial moist static energy flux compensates partly for the aerosol radiative cooling in the Northern Hemisphere. In contrast, the less restricted zonally asymmetrical circulation does not show sensitivity to the spatial structure of aerosols and strengthens in both hemispheres. The results also point to the possible role of aerosols in driving the observed reduction in the equatorial sea level pressure gradient. These circulation changes have profound implications for the hydrological cycle. Aerosols alone make the subtropical dry zones in both hemispheres wetter, as the local hydrological response is controlled thermodynamically by atmospheric moisture content. The deep tropical rainfall undergoes a dynamically induced southward shift, a robust pattern consistent with the adjustments in the zonal-mean circulation and in the meridional moist static energy transport. Less certain is the magnitude of the shift. The nonlinearity exhibited by the combined hydrological response to aerosols and radiatively active gases is dynamical in nature.

scholarly journals Simple Estimates of Polar Amplification in Moist Diffusive Energy Balance Models

2018 ◽  
Vol 31 (15) ◽  
pp. 5811-5824 ◽  
Author(s):  
Timothy M. Merlis ◽  
Matthew Henry
Keyword(s):  
Energy Balance ◽  
General Circulation ◽  
Energy Transport ◽  
Circulation Model ◽  
Thermodynamic Quantity ◽  
Solar Radiation Management ◽  
Moist Static Energy ◽  
Polar Amplification ◽  
Energy Balance Models ◽  
Static Energy

Diffusive energy balance models (EBMs) that use moist static energy, rather than temperature, as the thermodynamic variable to determine the energy transport provide an idealized framework to understand the pattern of radiatively forced surface warming. These models have a polar amplified warming pattern that is quantitatively similar to general circulation model simulations. Even without surface albedo changes or other spatially varying feedbacks, they simulate polar amplification that results from increased poleward energy transport with warming. Here, two estimates for polar amplification are presented that do not require numerical solution of the EBM governing equation. They are evaluated relative to the results of numerical moist EBM solutions. One estimate considers only changes in a moist thermodynamic quantity (assuming that the increase in energy transport results in a spatially uniform change in moist static energy in the warmed climate) and has more polar amplification than the EBM solution. The other estimate uses a new solution of a truncated form of the moist EBM equation, which allows for a temperature change that is consistent with both the dry and latent energy transport changes, as well as radiative changes. The truncated EBM solution provides an estimate for polar amplification that is nearly identical to that of the numerical EBM solution and only depends on the EBM parameters and climatology of temperature. This solution sheds light on the dependence of polar amplification on the climatological temperature distribution and offers an estimate of the residual polar warming in solar radiation management geoengineered climates.

A Gray-Radiation Aquaplanet Moist GCM. Part II: Energy Transports in Altered Climates

2007 ◽  
Vol 64 (5) ◽  
pp. 1680-1693 ◽  
Author(s):  
Dargan M. W. Frierson ◽  
Isaac M. Held ◽  
Pablo Zurita-Gotor
Keyword(s):  
Water Vapor ◽  
Energy Flux ◽  
General Circulation ◽  
Energy Transport ◽  
Circulation Model ◽  
Moisture Flux ◽  
Moist Static Energy ◽  
Meridional Transport ◽  
Total Energy Flux ◽  
Static Energy

Abstract A simplified moist general circulation model is used to study changes in the meridional transport of moist static energy by the atmosphere as the water vapor content is increased. The key assumptions of the model are gray radiation, with water vapor and other constituents having no effect on radiative transfer, and mixed layer aquaplanet boundary conditions, implying that the atmospheric meridional energy transport balances the net radiation at the top of the atmosphere. These simplifications allow the authors to isolate the effect of moisture on energy transports by baroclinic eddies in a relatively simple setting. The authors investigate the partition of moist static energy transport in the model into dry static energy and latent energy transports as water vapor concentrations are increased, by varying a constant in the Clausius–Clapeyron relation. The increase in the poleward moisture flux is rather precisely compensated by a reduction in the dry static energy flux. These results are interpreted with diffusive energy balance models (EBMs). The simplest of these is an analytic model that has the property of exact invariance of total energy flux as the moisture content is changed, but the assumptions underlying this model are not accurately satisfied by the GCM. A more complex EBM that includes expressions for the diffusivity, length scale, velocity scale, and latitude of maximum baroclinic eddy activity provides a better fit to the GCM’s behavior.

scholarly journals Monsoon Dynamics with Interactive Forcing. Part II: Impact of Eddies and Asymmetric Geometries

2007 ◽  
Vol 64 (5) ◽  
pp. 1431-1442 ◽  
Author(s):  
Nikki C. Privé ◽  
R. Alan Plumb
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Three Dimensional ◽  
Circulation Model ◽  
Qualitative Behavior ◽  
Monsoon Circulation ◽  
Moist Static Energy ◽  
Momentum Budget ◽  
Moist Static Energy Budget ◽  
Static Energy

Abstract The roles of eddies and forcing asymmetry in the dynamics of the large-scale monsoon circulation are investigated with a general circulation model. The net impact of eddies is found to be a slight weakening of the zonal mean monsoon circulation. The eddies strongly impact the momentum budget of the circulation, but the qualitative behavior of the monsoon flow is not substantially altered. The introduction of asymmetric forcing reveals the limitations of axisymmetric studies in representing the fully three-dimensional monsoon. Advection of low subcloud moist static energy air from the midlatitude oceans is seen to strongly impact the subcloud moist static energy budget in the continental subtropics, limiting the poleward extent of the monsoon. The advection of low moist static energy air must be blocked by orography, or the source of low moist static energy air must be removed, in order to induce strong precipitation over the subtropical landmass. An equatorial SST gradient is needed to induce a cross-equatorial meridional monsoon circulation. The location of the maximum subcloud moist static energy remains a good indicator for the limit of the monsoon.

scholarly journals The Effects of the Spatial Distribution of Direct Anthropogenic Aerosols Radiative Forcing on Atmospheric Circulation

2018 ◽  
Vol 31 (17) ◽  
pp. 7129-7145 ◽  
Author(s):  
Rei Chemke ◽  
Guy Dagan
Keyword(s):  
Spatial Distribution ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Radiative Forcing ◽  
General Circulation ◽  
Circulation Model ◽  
Hadley Cell ◽  
Global Circulation Model ◽  
Anthropogenic Aerosols

The large uncertainty in estimating the global aerosol radiative forcing (ARF) is one of the major challenges the climate community faces for climate projection. While the global-mean ARF may affect global quantities such as surface temperature, its spatial distribution may result in local thermodynamical and, thus, dynamical changes. Future changes in aerosol emissions distribution could further modulate the atmospheric circulation. Here, the effects of the spatial distribution of the direct anthropogenic ARF are studied using an idealized global circulation model, forced by a range of estimated-ARF amplitudes, based on the Copernicus Atmosphere Monitoring Service data. The spatial distribution of the estimated-ARF is globally decomposed, and the effects of the different modes on the circulation are studied. The most dominant spatial distribution feature is the cooling of the Northern Hemisphere in comparison to the Southern Hemisphere. This induces a negative meridional temperature gradient around the equator, which modulates the mean fields in the tropics. The ITCZ weakens and shifts southward, and the Northern (Southern) Hemisphere Hadley cell strengthens (weakens). The localization of the ARF in the Northern Hemisphere midlatitudes shifts the subtropical jet poleward and strengthens both the eddy-driven jet and Ferrel cell, because of the weakening of high-latitude eddy fluxes. Finally, the larger aerosol concentration in Asia compared to North America results in an equatorial superrotating jet. Understanding the effects of the different modes on the general circulation may help elucidate the circulation’s future response to the projected changes in ARF distribution.

scholarly journals Moisture and Moist Static Energy Budgets of South Asian Monsoon Low Pressure Systems in GFDL AM4.0

2018 ◽  
Vol 75 (6) ◽  
pp. 2107-2123 ◽  
Author(s):  
Ángel F. Adames ◽  
Yi Ming
Keyword(s):  
General Circulation ◽  
Deep Convection ◽  
Linear Regression Analysis ◽  
Maximum Amplitude ◽  
Circulation Model ◽  
Radiative Heating ◽  
Eastern Coast ◽  
Energy Budgets ◽  
Moist Static Energy ◽  
Static Energy

Abstract The mechanisms that lead to the propagation of anomalous moisture and moist static energy (MSE) in monsoon low and high pressure systems, collectively referred to as synoptic-scale monsoonal disturbances (SMDs), are investigated using daily output fields from GFDL’s atmospheric general circulation model, version 4.0 (AM4.0). On the basis of linear regression analysis of westward-propagating rainfall anomalies of time scales shorter than 15 days, it is found that SMDs are organized into wave trains of three to four individual cyclones and anticyclones. These events amplify over the Bay of Bengal, reach a maximum amplitude over the eastern coast of India, and dissipate as they approach the Arabian Sea. The structure and propagation of the simulated SMDs resemble those documented in observations. It is found that moisture and MSE anomalies exhibit similar horizontal structures in the simulated SMDs, indicating that moisture is the leading contributor to MSE. Propagation of the moisture anomalies is governed by vertical moisture advection, while the MSE anomalies propagate because of horizontal advection of dry static energy by the anomalous winds. By combining the budgets, we interpret the propagation of the moisture anomalies in terms of lifting that is forced by horizontal dry static energy advection, that is, ascent along sloping isentropes. This process moistens the lower free troposphere, producing an environment that is more favorable to deep convection. Ascent driven by radiative heating is of primary importance to the maintenance of the moisture anomalies.

scholarly journals Mechanisms of Remote Tropical Surface Warming during El Niño

2005 ◽  
Vol 18 (20) ◽  
pp. 4130-4149 ◽  
Author(s):  
John C. H. Chiang ◽  
Benjamin R. Lintner
Keyword(s):  
El Niño ◽  
El Nino ◽  
Circulation Model ◽  
Tropospheric Temperature ◽  
Moist Static Energy ◽  
Tropical Circulation ◽  
Model Simulations ◽  
Surface Warming ◽  
The Pacific ◽  
Static Energy

Abstract The authors demonstrate through atmospheric general circulation model (the Community Climate Model version 3.10) simulations of the 1997/98 El Niño that the observed “remote” (i.e., outside the Pacific) tropical land and ocean surface warming appearing a few months after the peak of the El Niño event is causally linked to the Tropics-wide warming of the troposphere resulting from increased atmospheric heating in the Pacific, with the latter acting as a conduit for the former. Unlike surface temperature, the surface flux behavior in the remote Tropics in response to El Niño is complex, with sizable spatial variation and compensation between individual flux components; this complexity suggests a more fundamental control (i.e., tropospheric temperature) for the remote tropical surface warming. Over the remote oceans, latent heat flux acting through boundary layer humidity variations is the important regulator linking the surface warming in the model simulations to the tropospheric warming over the remote tropical oceans. Idealized 1997/98 El Niño simulations using an intermediate tropical circulation model (the Quasi-Equilibrium Tropical Circulation Model) in which individual surface fluxes are directly manipulated confirms this result. The findings over the remote ocean are consistent with the “tropospheric temperature mechanism” previously proposed for the tropical ENSO teleconnection, with equatorial planetary waves propagating tropospheric temperature anomalies from the eastern Pacific to the remote Tropics and moist convective processes mediating the troposphere-to-remote-surface connection. The latter effectively requires the boundary layer moist static energy to vary in concert with the free tropospheric moist static energy. Over the remote land regions, idealized model simulations suggest that sensible heat flux regulates the warming response to El Niño, though the underlying mechanism has not yet been fully determined.

Monsoon Dynamics with Interactive Forcing. Part I: Axisymmetric Studies

2007 ◽  
Vol 64 (5) ◽  
pp. 1417-1430 ◽  
Author(s):  
Nikki C. Privé ◽  
R. Alan Plumb
Keyword(s):  
Boundary Layer ◽  
Angular Momentum ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Meridional Flow ◽  
Monsoon Circulation ◽  
Moist Static Energy ◽  
Summer Hemisphere ◽  
Static Energy

Abstract The applicability of axisymmetric theory of angular momentum conserving circulations to the large-scale steady monsoon is studied in a general circulation model with idealized representations of continental geometry and simple physics. Results from an aquaplanet setup with localized subtropical forcing are compared with a continental case. It is found that the meridional circulation that develops is close to angular momentum conserving for cross-equatorial circulation cells, both in the aquaplanet and in the continental cases. The equator proves to be a substantial barrier to boundary layer meridional flow; flow into the summer hemisphere from the winter hemisphere tends to occur in the free troposphere rather than in the boundary layer. A theory is proposed to explain the location of the monsoon; assuming quasiequilibrium, the poleward boundary of the monsoon circulation is collocated with the maximum in subcloud moist static energy, with the monsoon rains occurring near and slightly equatorward of this maximum. The model results support this theory of monsoon location, and it is found that the subcloud moist static energy distribution is determined by a balance between surface forcing and advection by the large-scale flow.

scholarly journals Simulation of the isotopic composition of stratospheric water vapour – Part 1: Description and evaluation of the EMAC model

2015 ◽  
Vol 15 (10) ◽  
pp. 5537-5555 ◽  
Author(s):  
R. Eichinger ◽  
P. Jöckel ◽  
S. Brinkop ◽  
M. Werner ◽  
S. Lossow
Keyword(s):  
Isotopic Composition ◽  
Water Vapour ◽  
General Circulation ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
Isotope Ratios ◽  
Physical Fractionation ◽  
Water Isotopologues ◽  
Stratospheric Water Vapour

Abstract. This modelling study aims at an improved understanding of the processes that determine the water vapour budget in the stratosphere by means of the investigation of water isotope ratios. An additional (and separate from the actual) hydrological cycle has been introduced into the chemistry–climate model EMAC, including the water isotopologues HDO and H218O and their physical fractionation processes. Additionally an explicit computation of the contribution of methane oxidation to H2O and HDO has been incorporated. The model expansions allow detailed analyses of water vapour and its isotope ratio with respect to deuterium throughout the stratosphere and in the transition region to the troposphere. In order to assure the correct representation of the water isotopologues in the model's hydrological cycle, the expanded system has been evaluated in several steps. The physical fractionation effects have been evaluated by comparison of the simulated isotopic composition of precipitation with measurements from a ground-based network (GNIP) and with the results from the isotopologue-enabled general circulation model ECHAM5-wiso. The model's representation of the chemical HDO precursor CH3D in the stratosphere has been confirmed by a comparison with chemical transport models (1-D, CHEM2D) and measurements from radiosonde flights. Finally, the simulated stratospheric HDO and the isotopic composition of water vapour have been evaluated, with respect to retrievals from three different satellite instruments (MIPAS, ACE-FTS, SMR). Discrepancies in stratospheric water vapour isotope ratios between two of the three satellite retrievals can now partly be explained.

Sign in / Sign up

Export Citation Format

Share Document