On the Role of Planetary-Scale Waves in the Abrupt Seasonal Transition of the Northern Hemisphere General Circulation

Shaw, Tiffany A.

doi:10.1175/jas-d-13-0137.1

Cited by 56 publications

(59 citation statements)

References 52 publications

(62 reference statements)

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“…Additionally,

T_{eq}^{'}

specifies a wave number 2 perturbation in the NH subtropics to mimic the zonally asymmetric effect of Asian and North American monsoons [e.g., Shaw , ].

T_{eq}^{'} = \frac{π}{2} A_{0} scriptℋ (- \overset{t}{true}) \sin (2 λ) Φ (ϕ, p)

Here

scriptℋ

() is a Heaviside function.…”

Section: Idealized Model and Transport Diagnosticssupporting

confidence: 89%

The role of monsoon‐like zonally asymmetric heating in interhemispheric transport

2017

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While the importance of the seasonal migration of the zonally averaged Hadley circulation on interhemispheric transport of trace gases has been recognized, few studies have examined the role of the zonally asymmetric monsoonal circulation. This study investigates the role of monsoon‐like zonally asymmetric heating on interhemispheric transport using a dry atmospheric model that is forced by idealized Newtonian relaxation to a prescribed radiative equilibrium temperature. When only the seasonal cycle of zonally symmetric heating is considered, the mean age of air in the Southern Hemisphere since last contact with the Northern Hemisphere midlatitude boundary layer is much larger than the observations. The introduction of monsoon‐like zonally asymmetric heating not only reduces the mean age of tropospheric air to more realistic values but also produces an upper tropospheric cross‐equatorial transport pathway in boreal summer that resembles the transport pathway simulated in the NASA Global Modeling Initiative Chemistry Transport Model driven with Modern‐Era Retrospective Analysis for Research and Applications meteorological fields. These results highlight that the monsoon‐induced eddy circulation plays an important role in the interhemispheric transport of long‐lived chemical constituents.

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“…Additionally,

T_{eq}^{'}

specifies a wave number 2 perturbation in the NH subtropics to mimic the zonally asymmetric effect of Asian and North American monsoons [e.g., Shaw , ].

T_{eq}^{'} = \frac{π}{2} A_{0} scriptℋ (- \overset{t}{true}) \sin (2 λ) Φ (ϕ, p)

Here

scriptℋ

() is a Heaviside function.…”

Section: Idealized Model and Transport Diagnosticssupporting

confidence: 89%

The role of monsoon‐like zonally asymmetric heating in interhemispheric transport

2017

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“…Climate) and land-sea thermal contrast (Shaw 2014). It remains an open problem to understand how the zonally asymmetric hydrological cycle in the real world responds to climate change in the presence of all of these different forcings.…”

Section: Discussionmentioning

confidence: 99%

How Stationary Eddies Shape Changes in the Hydrological Cycle: Zonally Asymmetric Experiments in an Idealized GCM

Wills

Schneider

2016

Journal of Climate

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Stationary and low-frequency Rossby waves are the primary drivers of extratropical weather variations on monthly and longer time scales. They take the form of persistent highs and lows, which, for example, shape subtropical dry zones and guide extratropical storms. More generally, stationary-eddy circulations, including zonally anomalous tropical overturning circulations, set up large zonal variations in net precipitation (precipitation minus evaporation, P 2 E). This paper investigates the response of stationary eddies and the zonally asymmetric hydrological cycle to global warming in an idealized GCM, simulating a wide range of climates by varying longwave absorption. The stationary eddies are forced by two idealized zonal asymmetries: a midlatitude Gaussian mountain and an equatorial ocean heat source. Associated with changes in stationary eddies are changes in the zonal variation of the hydrological cycle. Particularly in the subtropics, these simulations show a nearly constant or decreasing amplitude of the zonally anomalous hydrological cycle in climates warmer than modern despite the wet gets wetter, dry gets drier effect associated with increasing atmospheric moisture content. An approximation for zonally anomalous P 2 E, based on zonal-mean surface specific humidity and stationary-eddy vertical motion, disentangles the roles of thermodynamic and dynamic changes. The approximation shows that changes in the zonally asymmetric hydrological cycle are predominantly controlled by changes in lower-tropospheric vertical motion in stationary eddies.

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“…For example, the summer monsoons extend farther poleward in the eastern than western side of a major continent like the Afro-Eurasian. [49][50][51] Thus, expanding the zonal-mean energetics framework to two horizontal dimensions is required for predictions of regional rainfall changes in the tropics, say by accounting for the zonal component of divergent AET. 46,52 The application of the energetics framework is further complicated by ocean dynamical feedback.…”

Section: Limitations and Ways Forwardmentioning

confidence: 99%

Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

2018

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Intense tropical rainfall occurs in a narrow belt near the equator, called the inter-tropical convergence zone (ITCZ). In the past decade, the atmospheric energy budget has been used to explain changes in the zonal-mean ITCZ position. The energetics framework provides a mechanism for extratropics-to-tropics teleconnections, which have been postulated from paleoclimate records. In atmosphere models coupled with a motionless slab ocean, the ITCZ shifts toward the warmed hemisphere in order for the Hadley circulation to transport energy toward the colder hemisphere. However, recent studies using fully coupled models show that tropical rainfall can be rather insensitive to extratropical forcing when ocean dynamics is included. Here, we explore the effect of meridional Ekman heat advection while neglecting the upwelling effect on the ITCZ response to prescribed extratropical thermal forcing. The tropical component of Ekman advection is a negative feedback that partially compensates the prescribed forcing, whereas the extratropical component is a positive feedback that amplifies the prescribed forcing. Overall, the tropical negative feedback dominates over the extratropical positive feedback. Thus, including Ekman advection reduces the need for atmospheric energy transport, dampening the ITCZ response. We propose to build a hierarchy of ocean models to systematically explore the full dynamical response of the coupled climate system.

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On the Role of Planetary-Scale Waves in the Abrupt Seasonal Transition of the Northern Hemisphere General Circulation

Cited by 56 publications

References 52 publications

The role of monsoon‐like zonally asymmetric heating in interhemispheric transport

The role of monsoon‐like zonally asymmetric heating in interhemispheric transport

How Stationary Eddies Shape Changes in the Hydrological Cycle: Zonally Asymmetric Experiments in an Idealized GCM

Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

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