Cloud-Radiative Impacts On Tropical Circulation Change in GFDL AM4.1

2020 ◽  
Author(s):  
Juho Iipponen ◽  
Leo Donner
Keyword(s):  
Walker Circulation ◽  
Atmospheric Model ◽  
Hadley Cell ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Tropical Circulation ◽  
The North ◽  
Microphysical Properties ◽  
Tropospheric Circulation ◽  
Gross Moist Stability ◽  
The Impact

<pre>We use the Geophysical Fluid Dynamics Laboratory (GFDL) state-of-the-art AM4.1 atmospheric model to assess the impact of clouds on the change in tropical circulation. Slab-ocean experiments where cloud microphysical properties are locked to either the pre-industrial or 4xCO<sub>2</sub> conditions allow us to cleanly separate the circulation changes into a part caused by the cloud radiative effects (CREs), and to a part caused by the CO<sub>2</sub> changes. The CO<sub>2</sub>-induced SST changes are shown to dominate the response in the boundary layer, but are rivaled by the impacts of CREs in the mid to upper troposphere. The reduction in the east-to-west sea level pressure difference over the Pacific is solely caused by the increasing CO<sub>2</sub> and SST, but they only account for about half of the change in the mid-tropospheric Walker circulation. The weakening of the free-tropospheric circulation is shown to be mostly caused by the near-equal contributions the CO<sub>2</sub> and CREs make to the changes in dry-static and gross moist stability. Also, concerning the <span>meridional</span> circulation, we show that the response in the strength of the southern branch of the Hadley cell is largely due to CREs, while they have a much smaller impact in the north.</pre>

scholarly journals Mechanisms for Tropical Tropospheric Circulation Change in Response to Global Warming*

2012 ◽  
Vol 25 (8) ◽  
pp. 2979-2994 ◽  
Author(s):  
Jian Ma ◽  
Shang-Ping Xie ◽  
Yu Kosaka
Keyword(s):  
Global Warming ◽  
General Circulation ◽  
Vertical Motion ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Walker Circulation ◽  
Hadley Cell ◽  
Circulation Change ◽  
Tropospheric Circulation ◽  
Sst Warming

Abstract The annual-mean tropospheric circulation change in global warming is studied by comparing the response of an atmospheric general circulation model (GCM) to a spatial-uniform sea surface temperature (SST) increase (SUSI) with the response of a coupled ocean–atmosphere GCM to increased greenhouse gas concentrations following the A1B scenario. In both simulations, tropospheric warming follows the moist adiabat in the tropics, and static stability increases globally in response to SST warming. A diagnostic framework is developed based on a linear baroclinic model (LBM) of the atmosphere. The mean advection of stratification change (MASC) by climatological vertical motion, often neglected in interannual variability, is an important thermodynamic term for global warming. Once MASC effect is included, LBM shows skills in reproducing GCM results by prescribing latent heating diagnosed from the GCMs. MASC acts to slow down the tropical circulation. This is most clear in the SUSI run where the Walker circulation slows down over the Pacific without any change in SST gradient. MASC is used to decelerate the Hadley circulation, but spatial patterns of SST warming play an important role. Specifically, the SST warming is greater in the Northern than Southern Hemisphere, an interhemispheric asymmetry that decelerates the Hadley cell north, but accelerates it south of the equator. The MASC and SST-pattern effects are on the same order of magnitude in our LBM simulations. The former is presumably comparable across GCMs, while SST warming patterns show variations among models in both shape and magnitude. Uncertainties in SST patterns account for intermodel variability in Hadley circulation response to global warming (especially on and south of the equator).

scholarly journals An MSE budget view on seasonal and CO2-induced ITCZ shifts in the TRAC-MIP model ensemble

2020 ◽  
Author(s):  
Elzina Bala ◽  
Aiko Voigt ◽  
Peter Knippertz
Keyword(s):  
Vertical Velocity ◽  
Vertical Structure ◽  
Energy Transport ◽  
Atmospheric Model ◽  
Grand Challenge ◽  
Model Ensemble ◽  
Tropical Circulation ◽  
Tropical Rainfall ◽  
Mip Model ◽  
The Impact

<p>One of the grand challenges of climate is predicting and modeling tropical rainfall. Here, we address a specific problem of this grand challenge, namely how does the vertical structure of the atmosphere affect the tropical circulation and the position of the ITCZ during the seasonal cycle and in response to increased CO<sub>2</sub>. The tropical circulation can be described by the column-integrated budget of moist static energy (MSE). We use this framework in the TRAC-MIP model ensemble to investigate the role of the vertical structure of the tropical atmosphere in setting the anti-correlation between the ITCZ location and the atmospheric energy transport.</p><p>TRACMIP "The Tropical Rain belts with an Annual cycle and Continent - Model Intercomparison Project" is a set of idealized simulations that are designed to study the tropical rain belt response to past and future forcings. TRACMIP includes 13 comprehensive CMIP5-class atmosphere models and one simplified atmospheric model. Importantly, TRACMIP includes a slab ocean with prescribed ocean heat transport. This leads to a closed surface energy balance and forces the annual-mean ITCZ to be north of the equator, consistent with today’s climate.</p><p>We use the MSE budget framework to diagnose the seasonal evolution of vertical velocity from the energetic terms in the MSE budget equation. We obtain a diagnostic expression for the vertical velocity. By means of the MSE budget framework we estimate the efficiency of exporting energy from the atmospheric column, which is defined as the gross moist stability (GMS). The GMS characterizes the stability of the tropical troposphere related to moist convective processes in the tropospheric column. We use the MSE and GMS analysis to disentangle the impact of deep and shallow circulations on energy transport, vertical velocity and hence precipitation in an objective manner.</p><p>Through this work we aim to elucidate to what extent model uncertainty in simulations of future ITCZ changes are caused by model differences in the vertical structure of the atmosphere. We also hope to use the results to advance our understanding of the tropical climate and to assess the plausibility of simulated changes in tropical rainfall.</p>

scholarly journals ITCZ Width Controls on Hadley Cell Extent and Eddy-Driven Jet Position and Their Response to Warming

2019 ◽  
Vol 32 (4) ◽  
pp. 1151-1166 ◽  
Author(s):  
Oliver Watt-Meyer ◽  
Dargan M. W. Frierson
Keyword(s):  
Global Warming ◽  
Surface Temperature ◽  
Atmospheric Model ◽  
Hadley Cell ◽  
Lower Latitude ◽  
Tropical Precipitation ◽  
Highly Sensitive ◽  
Poleward Shift ◽  
The Impact ◽  
Zonal Momentum

The impact of global warming–induced intertropical convergence zone (ITCZ) narrowing onto the higher-latitude circulation is examined in the GFDL Atmospheric Model, version 2.1 (AM2.1), run over zonally symmetric aquaplanet boundary conditions. A striking reconfiguration of the deep tropical precipitation from double-peaked, off-equatorial ascent to a single peak at the equator occurs under a globally uniform +4 K sea surface temperature (SST) perturbation. This response is found to be highly sensitive to the SST profile used to force the model. By making small (≤1 K) perturbations to the surface temperature in the deep tropics, varying control simulation precipitation patterns with both single and double ITCZs are generated. Across the climatologies, narrower regions of ascent correspond to more equatorward Hadley cell edges and eddy-driven jets. Under the global warming perturbation, the experiments in which there is narrowing of the ITCZ show significantly less expansion of the Hadley cell and somewhat less poleward shift of the eddy-driven jet than those without ITCZ narrowing. With a narrower ITCZ, the ascending air has larger zonal momentum, causing more westerly upper-tropospheric subtropical wind. In turn, this implies 1) the subtropical jet will become baroclinically unstable at a lower latitude and 2) the critical (zero wind) line will shift equatorward, allowing midlatitude eddies to propagate farther equatorward. Both of these mechanisms modify the Hadley cell edge position, and the latter affects the jet position.

scholarly journals The Long- and Short-Lived North Atlantic Oscillation Events in a Simplified Atmospheric Model

2019 ◽  
Vol 76 (9) ◽  
pp. 2673-2700 ◽  
Author(s):  
Jie Song
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Early Stage ◽  
Atmospheric Model ◽  
Boreal Winter ◽  
Geophysical Fluid Dynamics Laboratory ◽  
The North ◽  
Northern Hemisphere Annular Mode ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract This study investigates the North Atlantic Oscillation (NAO) events with relatively long and short lifetimes based on an 8000-day perpetual-boreal-winter [December–February (DJF)] run result of the idealized Geophysical Fluid Dynamics Laboratory (GFDL) dynamical core atmospheric model. We identify the so-called long- and short-lived positive and negative NAO events from the 8000-day model output. The composite 300-hPa geopotential height anomalies show that the spatial patterns of the composite long-lived NAO events closely resemble the Northern Hemisphere annular mode (NAM) because the NAO dipole is accompanied with a statistically significant North Pacific meridional dipole (NPMD) at similar latitudes as that of the NAO dipole. The composite short-lived NAO events exhibit the locally confined canonical NAO. Twelve sets of modified initial-value experiments indicate that an absence (a presence) of the NPMD-type perturbations at the early stage of the long (short)-lived NAO events will decrease (increase) their intensities and naturally shorten (lengthen) their lifetimes. Thus, the preceding NPMD is an early factor that is conducive to the emergence of the long-lived NAO events in the model. We argue that through directly modulating the synoptic eddy forcing over the North Atlantic region, the preceding NPMD can gradually arouse the NAO-like circulation anomalies on the following days. That is the reason why the preceding NPMD can modulate the intensities and lifetimes of the NAO events.

scholarly journals Probing the Response of Tropical Deep Convection to Aerosol Perturbations Using Idealized Cloud-Resolving Simulations with Parameterized Large-Scale Dynamics

2019 ◽  
Vol 76 (9) ◽  
pp. 2885-2897
Author(s):  
Usama M. Anber ◽  
Shuguang Wang ◽  
Pierre Gentine ◽  
Michael P. Jensen
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Diabatic Heating ◽  
Deep Convection ◽  
Cloud Droplets ◽  
Aerosol Loading ◽  
Microphysical Properties ◽  
Tropical Deep Convection ◽  
Gross Moist Stability ◽  
The Impact

Abstract A framework is introduced to investigate the indirect effect of aerosol loading on tropical deep convection using three-dimensional limited-domain idealized cloud-system-resolving model simulations coupled with large-scale dynamics over fixed sea surface temperature. The large-scale circulation is parameterized using the spectral weak temperature gradient (WTG) approximation that utilizes the dominant balance between adiabatic cooling and diabatic heating in the tropics. The aerosol loading effect is examined by varying the number of cloud condensation nuclei (CCN) available to form cloud droplets in the two-moment bulk microphysics scheme over a wide range of environments from 30 to 5000 cm−3. The radiative heating is held at a constant prescribed rate in order to isolate the microphysical effects. Analyses are performed over the period after equilibrium is achieved between convection and the large-scale environment. Mean precipitation is found to decrease modestly and monotonically when the aerosol number concentration increases as convection gets weaker, despite the increase in cloud liquid water in the warm-rain region and ice crystals aloft. This reduction is traced down to the reduction in surface enthalpy fluxes as an energy source to the atmospheric column induced by the coupling of the large-scale motion, though the gross moist stability remains constant. Increasing CCN concentration leads to 1) a cooler free troposphere because of a reduction in the diabatic heating and 2) a warmer boundary layer because of suppressed evaporative cooling. This dipole temperature structure is associated with anomalously descending large-scale vertical motion above the boundary layer and ascending motion at lower levels. Sensitivity tests suggest that changes in convection and mean precipitation are unlikely to be caused by the impact of aerosols on cloud droplets and microphysical properties but rather by accounting for the feedback from convective adjustment with the large-scale dynamics. Furthermore, a simple scaling argument is derived based on the vertically integrated moist static energy budget, which enables estimation of changes in precipitation given known changes in surfaces enthalpy fluxes and the constant gross moist stability. The impact on cloud hydrometeors and microphysical properties is also examined, and it is consistent with the macrophysical picture.

scholarly journals Spectral optical layer properties of cirrus from collocated airborne measurements – a feasibility study

2015 ◽  
Vol 15 (13) ◽  
pp. 19045-19077 ◽  
Author(s):  
F. Finger ◽  
F. Werner ◽  
M. Klingebiel ◽  
A. Ehrlich ◽  
E. Jäkel ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Late Summer ◽  
Cloud Particle ◽  
Airborne Measurements ◽  
The North ◽  
Microphysical Properties ◽  
Research Aircraft ◽  
Irradiance Data ◽  
Optical Layer ◽  
The Impact

Abstract. Spectral optical layer properties of cirrus are derived from simultaneous and vertically collocated measurements of spectral upward and downward solar irradiance above and below the cloud layer and concurrent in situ microphysical sampling. From the irradiance data spectral transmissivity, absorptivity, reflectivity, and cloud top albedo of the observed cirrus layer are obtained. At the same time microphysical properties of the cirrus were sampled. The close collocation of the radiative and microphysical measurements, above, beneath and inside the cirrus, is obtained by using a research aircraft (Learjet 35A) in tandem with a towed platform called AIRTOSS (AIRcraft TOwed Sensor Shuttle). AIRTOSS can be released from and retracted back to the research aircraft by means of a cable up to a distance of 4 km. Data were collected in two field campaigns above the North and Baltic Sea in spring and late summer 2013. Exemplary results from one measuring flight are discussed also to illustrate the benefits of collocated sampling. Based on the measured cirrus microphysical properties, radiative transfer simulations were applied to quantify the impact of cloud particle properties such as crystal shape, effective radius reff, and optical thickness τ on cirrus optical layer properties. The effects of clouds beneath the cirrus are evaluated in addition. They cause differences in the layer properties of the cirrus by a factor of 2 to 3, and for cirrus radiative forcing by up to a factor of 4. If low-level clouds below cirrus are not considered the solar cooling due to the cirrus is significantly overestimated.

scholarly journals Impact of ocean-atmosphere coupling on regional climate: the Iberian Peninsula case

2020 ◽  
Author(s):  
William Cabos ◽  
Dmitry Sein ◽  
Alba de la Vara ◽  
Francisco Alvarez Garcia
Keyword(s):  
Atlantic Ocean ◽  
Iberian Peninsula ◽  
North Atlantic ◽  
Global Climate Model ◽  
Regional Climate ◽  
Atmospheric Model ◽  
The North ◽  
Regional Atmospheric Model ◽  
The North Atlantic ◽  
The Impact

<p>Regional models used for downscaling the European climate usually include a relatively small area of the Atlantic Ocean and are uncoupled, with the SST used as lower boundary conditions much coarser than the mesh of the regional atmospheric model. Concerns thus arise about the proper representation of the oceanic influence and the role of air-sea coupling in such experiments.  A complex orography and the exposure to different air and ocean masses make the Iberian Peninsula (IP) an ideal test case for exploring the impact of including explicitly the North Atlantic in the regional domain and the added value that coupling brings to regional climate modeling. To this end, the regionally-coupled model ROM and its atmospheric component, the regional atmospheric model REMO are used in a set of coupled and uncoupled experiments forced by the ERA-Interim reanalysis and by the global climate model MPI-ESM. The atmospheric domain is the same in all simulations and includes the North Atlantic and the ocean component is global and eddy permitting. Results show that the impact of air-sea coupling on the IP winter biases can be traced back to the features of the simulated North Atlantic Ocean circulation. In summer, it is the air-sea interactions in the Mediterranean that exert the largest influence on the regional biases. Despite improvements introduced by the eddy-permitting ocean, it is suggested that a higher resolution could be needed for a correct simulation of the features of the large-scale atmospheric circulation that impact the climate of the IP.     </p>

scholarly journals Sensitivity of nitrate aerosols to ammonia emissions and to nitrate chemistry: implications for present and future nitrate optical depth

2015 ◽  
Vol 15 (18) ◽  
pp. 25739-25788 ◽  
Author(s):  
F. Paulot ◽  
P. Ginoux ◽  
W. F. Cooke ◽  
L. J. Donner ◽  
S. Fan ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Atmospheric Model ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Ammonia Emissions ◽  
Free Troposphere ◽  
Near Surface ◽  
Nitrate Concentrations ◽  
The Impact

Abstract. We update and evaluate the treatment of nitrate aerosols in the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model (AM3). Accounting for the radiative effects of nitrate aerosols generally improves the simulated aerosol optical depth, although nitrate concentrations at the surface are biased high. This bias can be reduced by increasing the deposition of nitrate to account for the near-surface volatilization of ammonium nitrate or by neglecting the heterogeneous production of nitric acid to account for the inhibition of N2O5 reactive uptake at high nitrate concentrations. Globally, uncertainties in these processes can impact the simulated nitrate optical depth by up to 25 %, much more than the impact of uncertainties in the seasonality of ammonia emissions (6 %) or in the uptake of nitric acid on dust (13 %). Our best estimate for present-day fine nitrate optical depth at 550 nm is 0.006 (0.005–0.008). We only find a modest increase of nitrate optical depth (< 30 %) in response to the projected changes in the emissions of SO2 (−40 %) and ammonia (+38 %) from 2010 to 2050. Nitrate burden is projected to increase in the tropics and in the free troposphere, but to decrease at the surface in the midlatitudes because of lower nitric acid concentrations. Our results suggest that better constraints on the heterogeneous chemistry of nitric acid on dust, on tropical ammonia emissions, and on the transport of ammonia to the free troposphere are needed to improve projections of aerosol optical depth.

The Tropical Precipitation Response to Andes Topography and Ocean Heat Fluxes in an Aquaplanet Model

2014 ◽  
Vol 28 (1) ◽  
pp. 381-398 ◽  
Author(s):  
Elizabeth A. Maroon ◽  
Dargan M. W. Frierson ◽  
David S. Battisti
Keyword(s):  
Energy Transport ◽  
Atmospheric Model ◽  
Heat Fluxes ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Ocean Energy ◽  
Tropical Rainfall ◽  
Tropical Precipitation ◽  
The North ◽  
The Andes ◽  
Precipitation Response

Abstract This aquaplanet modeling study using the Geophysical Fluid Dynamics Laboratory Atmospheric Model, version 2.1 (GFDL AM2.1), examines how ocean energy transport and topography influence the location of tropical precipitation. Adding realistic Andes topography regionally displaces tropical rainfall from the equator into the Northern Hemisphere, even when the wind–evaporation feedback is disabled. The relative importance of the Andes compared to the asymmetric hemispheric heating of the atmosphere by ocean transport is examined by including idealized and realistic zonally averaged surface heat fluxes (also known as q fluxes) in the slab ocean. A hemispherically asymmetric q flux displaces the tropical rainfall toward the hemisphere receiving the greatest heating by the ocean. The zonal-mean displacement of rainfall is greater in simulations with a realistic q flux than with a realistic Andes topography. Simulations that add both a q flux and topography displace rainfall farther to the north in the region 120° to the west of the Andes than in simulations that only have a q flux. Cloud and clear-sky radiative feedbacks in the tropics and subtropics of this model both act to amplify the energy flux and the precipitation response to a given hemispheric asymmetry in oceanic forcing.

scholarly journals Characterizing the Hadley Circulation Response through Regional Climate Feedbacks

2016 ◽  
Vol 29 (2) ◽  
pp. 613-622 ◽  
Author(s):  
N. Feldl ◽  
S. Bordoni
Keyword(s):  
Radiative Forcing ◽  
Hydrological Cycle ◽  
Hadley Circulation ◽  
Hadley Cell ◽  
Lapse Rate ◽  
Climate Feedbacks ◽  
Ocean Heat Uptake ◽  
Eddy Heat Flux ◽  
Gross Moist Stability ◽  
The Impact

Abstract The robust weakening of the tropical atmospheric circulation in projections of anthropogenic warming is associated with substantial changes in regional and global climate. The present study focuses on understanding the response of the annual-mean Hadley circulation from a perspective of interactions between climate feedbacks and tropical circulation. Simulations from an ensemble of coupled ocean–atmosphere models are used to quantify changes in Hadley cell strength in terms of feedbacks, radiative forcing, ocean heat uptake, atmospheric eddies, and gross moist stability. Climate feedbacks are calculated for the model integrations from phase 5 of CMIP (CMIP5) using radiative kernels. Tropical mean circulation is found to be reduced by up to 2.6% K−1 for an abrupt quadrupling of carbon dioxide concentration. The weakening is characterized by an increase in gross moist stability, by an increase in eddy heat flux, and by positive extratropical feedbacks, such as those associated with lapse rate and sea ice response. Understanding the impact of radiative feedbacks on the large-scale circulation provides a framework for constraining uncertainty in the dynamic climate response, including the hydrological cycle.

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