Previous work has shown that the Madden‐Julian Oscillation (MJO) can influence the North Atlantic Oscillation (NAO) via a Rossby wave teleconnection that propagates through the troposphere (i.e., a tropospheric pathway). In addition, recent work suggests that the MJO can influence the stratospheric polar vortex, which is also known to influence the tropospheric NAO—thus, there likely exists a stratospheric pathway for MJO influence as well. Here, we apply two methods to shed more light on the pathways linking the MJO to the NAO. First, we use a traditional approach in climate science based on analyzing conditional probabilities. Second, we use methods from causal discovery theory based on probabilistic graphical models. Together, these two analysis approaches reveal that the MJO can impact the NAO via both a tropospheric and stratospheric pathway. The stratospheric pathway is shown to come about in two ways: First, both methods show that the MJO itself influences the strength of the stratospheric polar vortex on a timescale of ∼10 days, and then 5 days later the vortex can drive changes in the NAO. Second, the state of the stratospheric polar vortex acts to condition the NAO to be conducive (or not) to MJO influence. When the vortex is in a state that opposes the expected NAO response to the MJO, we find little influence of the MJO on the NAO, however, when the vortex supports the expected NAO response, the NAO is up to 30% more likely to be in a particular state following active MJO periods.

Abstract. High-resolution Earth system model simulations generate enormous data volumes, and retaining the data from these simulations often strains institutional storage resources. Further, these exceedingly large storage requirements negatively impact science objectives, for example, by forcing reductions in data output frequency, simulation length, or ensemble size. To lessen data volumes from the Community Earth System Model (CESM), we advocate the use of lossy data compression techniques. While lossy data compression does not exactly preserve the original data (as lossless compression does), lossy techniques have an advantage in terms of smaller storage requirements. To preserve the integrity of the scientific simulation data, the effects of lossy data compression on the original data should, at a minimum, not be statistically distinguishable from the natural variability of the climate system, and previous preliminary work with data from CESM has shown this goal to be attainable. However, to ultimately convince climate scientists that it is acceptable to use lossy data compression, we provide climate scientists

This paper investigates causal links between Arctic temperatures and the jet streams. We apply two different frameworks for this application based on the concepts of (1) Granger causality and (2) Pearl causality. Both methods show that Arctic temperature and jet speed and position all exhibit strong autocorrelation, but they also show that these variables are linked together by two robust positive feedback loops that operate on time scales of 5–25 days. The dynamical implications of these feedbacks are discussed. This study is only the beginning of a larger effort to apply and compare different causality methods in order to gain a deeper understanding of the causal connections between the Arctic and weather at lower latitudes.

The Madden-Julian oscillation (MJO) has long been identified as an important source of midlatitude weather predictability on subseasonal-to-seasonal (S2S) timescales (∼2 weeks to 3 months) via its teleconnections to higher latitudes. Tropical convection associated with the MJO slowly propagates eastward in a quasiperiodic manner, taking ∼20-90 days to circumnavigate the globe and complete a cycle (Madden & Julian, 1971, 1972; Zhang, 2013). MJO activity can excite Rossby waves which propagate out of the tropics and into the midlatitudes, modifying the large-scale circulation and weather patterns. Because it can take 10-15 days for the teleconnection to reach the midlatitudes, knowing the state of the MJO today can provide information about the evolution of the midlatitude flow in the coming weeks. In fact, multiple studies have demonstrated that the MJO can be used to make skillful forecasts of weather up to 5 weeks in advance across the