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.

The Total Meridional Heat Flux and Its Oceanic and Atmospheric Partition

2005 ◽  
Vol 18 (21) ◽  
pp. 4374-4380 ◽  
Author(s):  
Carl Wunsch
Keyword(s):  
Northern Hemisphere ◽  
Energy Transport ◽  
Atmospheric Model ◽  
Heat Fluxes ◽  
Radiation Budget ◽  
Meridional Heat Transport ◽  
Atmospheric Flux ◽  
Oceanic Surface ◽  
Earth Radiation Budget ◽  
Estimated Error

Abstract Atmospheric meridional heat transport is inferred as a residual from the Earth Radiation Budget Experiment (ERBE) data and in situ oceanic estimates. Reversing the conventional approach of computing the ocean as an atmospheric model residual is done to permit calculation of a preliminary uncertainty estimate for the atmospheric flux. The structure of the ERBE errors is itself an important uncertainty. Total energy transport is almost indistinguishable from a hemispherically antisymmetric analytic function, despite the great asymmetry of the oceanic heat fluxes. ERBE data appear sufficiently noisy so that a considerable range of atmospheric transports remains possible: the maximum atmospheric value lies between 3 and 5 PW in the Northern Hemisphere, at one standard deviation, although the values are sensitive to the noise assumptions made here. The Northern Hemisphere ocean and atmosphere carry comparable poleward heat fluxes to about 28°N where the oceanic flux drops rapidly, but does not actually vanish until the oceanic surface area goes to zero. Within the estimated error bars, there is a remarkable antisymmetry about the equator of the combined ocean and atmospheric transports, despite the marked oceanic transport asymmetry.

Dynamic and energetic constraints on the modality and position of the intertropical convergence zone in an aquaplanet

2020 ◽  
Author(s):  
Ori Adam ◽  
Hilla Gerstman
Keyword(s):  
Energy Transport ◽  
Hadley Circulation ◽  
Coupled System ◽  
Ocean Energy ◽  
Ocean Stratification ◽  
Tropical Precipitation ◽  
Double Peaks ◽  
Root Relation ◽  
Convergence Zones ◽  
Asymmetric Heating

<p>The tropical zonal-mean precipitation distribution can vary between single and double peaks, which are associated with intertropical convergence zones (ITCZs). Here, the meridional modality and the sensitivity to hemispherically-asymmetric heating of tropical precipitation is studied in an idealized GCM with parameterized wind-driven ocean energy transport (OET). In the idealized model, transitions from unimodal to bimodal distributions are driven by equatorial ocean upwelling and cooling which inhibits equatorial precipitation. For sufficiently strong cooling, the circulation bifurcates to anti-Hadley circulation (AHC) in the deep tropics, with a descending branch near the equator and off-equatorial double ITCZs. The intensity of the AHC is limited by a negative feedback: the AHC drives westerly surface winds which balance the easterly stress (and hence equatorial upwelling) required for its maintenance. The modality of the precipitation affects the response to asymmetric heating: For weak ocean stratification, OET damps shifts of the tropical precipitation centroid but amplifies shifts of precipitation peaks. For strong ocean stratification, which leads to double ITCZs, asymmetric heating leads to relative intensification of the ITCZ in the warming hemisphere, but the positions of the double ITCZs are insensitive to changes in the asymmetric heating and ocean stratification. The dynamic feedbacks of the coupled system damp the slope of the atmospheric energy transport (AET) near the equator. This justifies a cubic root relation between the cross-equatorial AET and the position of the ITCZ, which captures migrations of the ITCZ significantly better than the commonly-used linear relation.</p>

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 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.

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 The Tropical Response to Extratropical Thermal Forcing in an Idealized GCM: The Importance of Radiative Feedbacks and Convective Parameterization

2009 ◽  
Vol 66 (9) ◽  
pp. 2812-2827 ◽  
Author(s):  
Sarah M. Kang ◽  
Dargan M. W. Frierson ◽  
Isaac M. Held
Keyword(s):  
Water Vapor ◽  
Energy Transport ◽  
Convection Scheme ◽  
Thermal Forcing ◽  
Low Level ◽  
Tropical Precipitation ◽  
Idealized Model ◽  
Flux Change ◽  
Precipitation Response ◽  
Atmospheric Energy Transport

Abstract The response of tropical precipitation to extratropical thermal forcing is reexamined using an idealized moist atmospheric GCM that has no water vapor or cloud feedbacks, simplifying the analysis while retaining the aquaplanet configuration coupled to a slab ocean from the authors’ previous study. As in earlier studies, tropical precipitation in response to high-latitude forcing is skewed toward the warmed hemisphere. Comparisons with a comprehensive GCM in an identical aquaplanet, mixed-layer framework reveal that the tropical responses tend to be much larger in the comprehensive GCM as a result of positive cloud and water vapor feedbacks that amplify the imposed extratropical thermal forcing. The magnitude of the tropical precipitation response in the idealized model is sensitive to convection scheme parameters. This sensitivity as well as the tropical precipitation response can be understood from a simple theory with two ingredients: the changes in poleward energy fluxes are predicted using a one-dimensional energy balance model and a measure of the “total gross moist stability” [Δm, which is defined as the total (mean plus eddy) atmospheric energy transport per unit mass transport] of the model tropics converts the energy flux change into a mass flux and a moisture flux change. The idealized model produces a low level of compensation of about 25% between the imposed oceanic flux and the resulting response in the atmospheric energy transport in the tropics regardless of the convection scheme parameter. Because Geophysical Fluid Dynamics Laboratory Atmospheric Model 2 (AM2) with prescribed clouds and water vapor exhibits a similarly low level of compensation, it is argued that roughly 25% of the compensation is dynamically controlled through eddy energy fluxes. The sensitivity of the tropical response to the convection scheme in the idealized model results from different values of Δm: smaller Δm leads to larger tropical precipitation changes for the same response in the energy transport.

scholarly journals The Precipitation Response to an Idealized Subtropical Continent

2016 ◽  
Vol 29 (12) ◽  
pp. 4543-4564 ◽  
Author(s):  
Elizabeth A. Maroon ◽  
Dargan M. W. Frierson ◽  
Sarah M. Kang ◽  
Jacob Scheff
Keyword(s):  
General Circulation ◽  
Hadley Circulation ◽  
General Circulation Models ◽  
Atmospheric Model ◽  
Opposite Hemisphere ◽  
Clear Sky ◽  
Tropical Precipitation ◽  
Precipitation Response ◽  
Atmospheric General Circulation Models ◽  
The Impact

Abstract A subtropical continent is added to two aquaplanet atmospheric general circulation models (AGCMs) to better understand the influence of land on tropical circulation and precipitation. The first model, the gray-radiation moist (GRaM) AGCM, has simplified physics, while the second model, the GFDL Atmospheric Model version 2.1 (AM2.1), is a fully comprehensive AGCM. Both models have a continent that is 60° wide in longitude from 10° to 30°N, in an otherwise slab-ocean-covered world. The precipitation response varies with cloudy- and clear-sky feedbacks and depends on continental albedo. In GRaM simulations with a continent, precipitation in the Northern Hemisphere decreases mostly as a result of decreased evaporation. In AM2.1 simulations, precipitation also shifts southward via Hadley circulation changes due to increasing albedo, but the radiative impact of clouds and moisture creates a more complex response. Results are similar when a seasonal cycle of insolation is included in AM2.1 simulations. The impact of a large, bright subtropical continent is to shift precipitation to the opposite hemisphere. In these simulations, the hemisphere of greater tropical precipitation is better predicted by the hemisphere with greater atmospheric energy input, as has been shown in previous literature, rather than the hemisphere that has higher surface temperature.

Singa Transitional: Rock-art Saywas Marking Boundaries of Identity and Socializing Landscape in Huánuco, Peru

2021 ◽  
Vol 31 (2) ◽  
pp. 247-263
Author(s):  
Jonathan J. Dubois
Keyword(s):  
Material Culture ◽  
Rock Art ◽  
Social Changes ◽  
Regional Survey ◽  
Intermediate Period ◽  
Social Trends ◽  
The North ◽  
The Andes ◽  
Early Horizon ◽  
Landscape Feature

This paper introduces a new art style, Singa Transitional, found painted onto a mountainside near the modern town of Singa in the north of Huánuco, Peru. This style was discovered during a recent regional survey of rock art in the Huánuco region that resulted in the documentation of paintings at more than 20 sites, the identification of their chronological contexts and an analysis of the resulting data for trends in changing social practices over nine millennia. I explore how the style emerged from both regional artistic trends in the medium and broader patterns evident in Andean material culture from multiple media at the time of its creation. I argue that the presence of Singa Transitional demonstrates that local peoples were engaged in broader social trends unfolding during the transition between the Early Horizon (800–200 bc) and the Early Intermediate Period (ad 0–800) in Peru. I propose that rock art placed in prominent places was considered saywa, a type of landscape feature that marked boundaries in and movement through landscapes. Singa Transitional saywas served to advertise the connection between local Andean people and their land and was a medium through which social changes were contested in the Andes.

scholarly journals Distribution, ecology and conservation of an endangered Andean hummingbird: the Violet-throated Metaltail (Metallura baroni)

2009 ◽  
Vol 19 (1) ◽  
pp. 63-76 ◽  
Author(s):  
BORIS A. TINOCO ◽  
PEDRO X. ASTUDILLO ◽  
STEVEN C. LATTA ◽  
CATHERINE H. GRAHAM
Keyword(s):  
Suitable Habitat ◽  
Species Occurrence ◽  
Entropy Model ◽  
Maxent Model ◽  
The North ◽  
The Andes ◽  
Guide Field ◽  
South Central ◽  
Detailed Assessment ◽  
Endangered Status

SummaryThe Violet-throated MetaltailMetallura baroniis a high altitude hummingbird endemic to south-central Ecuador currently considered globally ‘Endangered’. Here we present the first detailed assessment of its distribution, ecology and conservation. We first used a maximum entropy model (Maxent model) to create a predicted distribution for this species based on very limited species occurrence data. We used this model to guide field surveys for the species between April and October 2006. We found a positive relationship between model values and species presence, indicating that the model was a useful tool to predict species occurrence and guide exploration. In the sites where the metaltail was found we gathered data on its habitat requirements, food resources and behaviour. Our results indicate that Violet-throated Metaltail is restricted to the Western Cordillera of the Andes Mountains in Azuay and Cañar provinces of Ecuador, with an area of extent of less than 2,000 km2. Deep river canyons to the north and south, lack of suitable habitat, and potential interspecific competition in the east may limit the bird's distribution. The species occurred in three distinct habitats, includingPolylepiswoodland, the upper edge of the montane forest, and in shrubby paramo, but we found no difference in relative abundance among these habitats. The metaltail seems to tolerate moderate human intervention in its habitats as long as some native brushy cover is maintained. We found thatBrachyotumsp.,Berberissp., andBarnadesiasp. were important nectar resources. The ‘Endangered’ status of this species is supported due to its restricted distribution in fragmented habitats which are under increasing human pressures.

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