A study of links between the Arctic and the midlatitude jet stream using Granger and Pearl causality

Samarasinghe, Savini M.; McGraw, Marie C.; Barnes, Elizabeth A.; Ebert‐Uphoff, Imme

doi:10.1002/env.2540

Cited by 22 publications

(22 citation statements)

References 55 publications

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“…In order to assess the causality of the surface impacts contemporaneous with and following ASO anomalies, we form a causal effect network following Pearl causality (Pearl, 2000). The relative benefits and drawbacks of Pearl causality and Granger causality are discussed in Runge et al (2018) and Samarasinghe et al (2018). For our particular application we are interested in evaluating whether ASO or dynamical variability (which we track using area-weighted geopotential height from 80 • N to the pole at 100 hPa, i.e., Zpole) leads to ENSO variability with leads of 10 to 27 months, i.e., whether ENSO has "parents".…”

Section: Methodsmentioning

confidence: 99%

Influence of Arctic stratospheric ozone on surface climate in CCMI models

et al. 2019

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Abstract. The Northern Hemisphere and tropical circulation response to interannual variability in Arctic stratospheric ozone is analyzed in a set of the latest model simulations archived for the Chemistry-Climate Model Initiative (CCMI) project. All models simulate a connection between ozone variability and temperature/geopotential height in the lower stratosphere similar to that observed. A connection between Arctic ozone variability and polar cap surface air pressure is also found, but additional statistical analysis suggests that it is mediated by the dynamical variability that typically drives the anomalous ozone concentrations. While the CCMI models also show a connection between Arctic stratospheric ozone and the El Niño–Southern Oscillation (ENSO), with Arctic stratospheric ozone variability leading to ENSO variability 1 to 2 years later, this relationship in the models is much weaker than observed and is likely related to ENSO autocorrelation rather than any forced response to ozone. Overall, Arctic stratospheric ozone is related to lower stratospheric variability. Arctic stratospheric ozone may also influence the surface in both polar and tropical latitudes, though ozone is likely not the proximate cause of these impacts and these impacts can be masked by internal variability if data are only available for ∼40 years.

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Section: Methodsmentioning

confidence: 99%

Influence of Arctic stratospheric ozone on surface climate in CCMI models

et al. 2019

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“…Tropical-mid-latitude teleconnections in boreal summer can have a great impact on surface weather conditions in the northern mid-latitudes (Ding and Wang, 2005;O'Reilly et al, 2018;Wang et al, 2001). Still, the direct influence of the El Niño-Southern Oscillation (ENSO) on the mid-latitude circulation is weaker in summer than in winter (Branstator, 2002;Schubert et al, 2011;Thomson and Vallis, 2018). Instead, in summer convective activity related to the Northern Hemisphere tropical monsoon systems can profoundly influence surface weather conditions in the mid-latitudes (Branstator, 2014;Ding and Wang, 2005;O'Reilly et al, 2018;Rodwell and Hoskins, 1996).…”

Section: Introductionmentioning

confidence: 99%

Dominant patterns of interaction between the tropics and mid-latitudes in boreal summer: causal relationships and the role of timescales

Capua

Runge

Donner

et al. 2020

Weather Clim. Dynam.

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Abstract. Tropical convective activity represents a source of predictability for mid-latitude weather in the Northern Hemisphere. In winter, the El Niño–Southern Oscillation (ENSO) is the dominant source of predictability in the tropics and extratropics, but its role in summer is much less pronounced and the exact teleconnection pathways are not well understood. Here, we assess how tropical convection interacts with mid-latitude summer circulation at different intra-seasonal timescales and how ENSO affects these interactions. First, we apply maximum covariance analysis (MCA) between tropical convective activity and mid-latitude geopotential height fields to identify the dominant modes of interaction. The first MCA mode connects the South Asian monsoon with the mid-latitude circumglobal teleconnection pattern. The second MCA mode connects the western North Pacific summer monsoon in the tropics with a wave-5 pattern centred over the North Pacific High in the mid-latitudes. We show that the MCA patterns are fairly insensitive to the selected intra-seasonal timescale from weekly to 4-weekly data. To study the potential causal interdependencies between these modes and with other atmospheric fields, we apply the causal discovery method PCMCI at different timescales. PCMCI extends standard correlation analysis by removing the confounding effects of autocorrelation, indirect links and common drivers. In general, there is a two-way causal interaction between the tropics and mid-latitudes, but the strength and sometimes sign of the causal link are timescale dependent. We introduce causal maps that show the regionally specific causal effect from each MCA mode. Those maps confirm the dominant patterns of interaction and in addition highlight specific mid-latitude regions that are most strongly connected to tropical convection. In general, the identified causal teleconnection patterns are only mildly affected by ENSO and the tropical mid-latitude linkages remain similar. Still, La Niña strengthens the South Asian monsoon generating a stronger response in the mid-latitudes, while during El Niño years the Pacific pattern is reinforced. This study paves the way for process-based validation of boreal summer teleconnections in (sub-)seasonal forecast models and climate models and therefore works towards improved sub-seasonal predictions and climate projections.

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“…The method is nonetheless useful for disentangling drivers from responses in ocean-ice-atmosphere interactions. Following prior work in the Arctic (Matthewman and Magnusdottir 2011;Kretschmer et al 2016;Samarasinghe et al 2018), we analyze the degree to which Weddell Sea polynyas drive and/or respond to climate variability in a comprehensive setting, enabling new insights into the elusive role that Weddell Sea convection can have in the high-latitude climate system.…”

Section: Introductionmentioning

confidence: 99%

Causal Interactions between Southern Ocean Polynyas and High-Latitude Atmosphere–Ocean Variability

et al. 2020

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Weddell Sea open-ocean polynyas have been observed to occasionally release heat from the deep ocean to the atmosphere, indicating that their sporadic appearances may be an important feature of high-latitude atmosphere–ocean variability. Yet, observations of the phenomenon are sparse and many standard-resolution models represent these features poorly, if at all. We use a fully coupled, synoptic-scale preindustrial control simulation of the Energy Exascale Earth System Model (E3SMv0-HR) to effectively simulate open-ocean polynyas and investigate their role in the climate system. Our approach employs statistical tests of Granger causality to diagnose local and remote drivers of, and responses to, polynya heat loss on interannual to decadal time scales. First, we find that polynya heat loss Granger causes a persistent increase in surface air temperature over the Weddell Sea, strengthening the local cyclonic wind circulation. Along with responding to polynyas, atmospheric conditions also facilitate their development. When the Southern Ocean experiences a rapid poleward shift in the circumpolar westerlies following a prolonged negative phase of the southern annular mode (SAM), Weddell Sea salinity increases, promoting density destratification and convection in the water column. Finally, we find that the reduction of surface heat fluxes during periods of full ice cover is not fully compensated by ocean heat transport into the high latitudes. This imbalance leads to a buildup of ocean heat content that supplies polynya heat loss. These results disentangle the complex, coupled climate processes that both enable the polynya’s existence and respond to it, providing insights to improve the representation of these highly episodic sea ice features in climate models.

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A study of links between the Arctic and the midlatitude jet stream using Granger and Pearl causality

Cited by 22 publications

References 55 publications

Influence of Arctic stratospheric ozone on surface climate in CCMI models

Influence of Arctic stratospheric ozone on surface climate in CCMI models

Dominant patterns of interaction between the tropics and mid-latitudes in boreal summer: causal relationships and the role of timescales

Causal Interactions between Southern Ocean Polynyas and High-Latitude Atmosphere–Ocean Variability

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