Here we show that the characteristics of the Indian Ocean Dipole (IOD), such as its power spectrum and phase relationship with the El Niño–Southern Oscillation (ENSO), can be succinctly explained by ENSO combination mode (C‐mode) wind and heat flux forcing together with a seasonal modulation of the air/sea coupled Indian Ocean (IO) Bjerknes feedback. This model explains the observed high‐frequency near‐annual IOD variability in terms of deterministic ENSO/annual cycle interactions. ENSO‐independent IOD events can be understood as a seasonally modulated ocean response to white noise atmospheric forcing. Under this new physical null hypothesis framework, IOD predictability is determined by both ENSO predictability and the ENSO signal‐to‐noise ratio. We further emphasize that lead/lag correlations between different climate variables are easily misinterpreted when not accounting properly for the seasonal modulation of the underlying climate phenomena.

Significant interhemispheric teleconnections are identified that span the tropical easterlies in the boreal summer 300-hPa streamfunction, such as the North Africa–Antarctic (NAA) and the North Pacific–South America (NPSA) patterns. These patterns are not supported by traditional wave theory, since stationary waves in a basic state without meridional wind would be trapped in the easterlies. To describe the interhemispheric responses more realistically, two-dimensional spherical Rossby wave theory in a horizontally nonuniform basic state is considered. Conditions sufficient for the existence of one propagating wave are obtained, and the meridional group velocity of the wave is shown to have the same direction as the meridional basic wind at the traditional critical latitude. It is concluded that stationary waves with a specific wavelength can propagate across the easterlies from south (north) to north (south) via southerly (northerly) flows. Hence, energy transport by stationary waves on a horizontally nonuniform basic state may produce interhemispheric responses that could pass through the tropical easterly belt. The wave theory and a barotropic model are then applied to idealized and climatological flows. Model results agree well with the theory. In boreal winter and summer, cross-equatorial flows steer stationary waves propagating from one hemisphere to the other across the tropical easterlies, especially over the Australian–Asian monsoon region. It seems that the large-scale monsoonal background flows play a critical role in the interhemispheric teleconnection. Additionally, the wave ray trajectory and model results suggest that the NAA pattern may result from Rossby wave energy dispersion.

The time series of 20th century Siberian warm season (May to October) precipitation (SWP) shows variations over decadal timescales, including a wetting trend since the 1970s. Here, it is shown that the Atlantic multidecadal variability (AMV) can be implicated as a remote driver of the decadal-scale variations in SWP. Observational analysis identifies a significant in-phase relationship between the AMV and SWP and the SWP decadal variability can be largely explained by the AMV. The physical mechanism for this relationship is investigated using both observations and numerical simulations. The results suggest that North Atlantic sea surface temperature (SST) warming associated with the positive AMV phase can excite an eastward propagating wave train response across the entire Eurasian continent, which includes an east–west dipole structure over Siberia. The dipole then leads to anomalous southerly winds bringing moisture northward to Siberia; the precipitation increases correspondingly. The mechanism is further supported by linear barotropic modeling and Rossby wave ray tracing analysis.

Haze is a serious issue in China with increasing concerns and understanding the factors driving decadal-scale variations in haze occurrence is relevant for government policymaking. Using a comprehensive observational haze dataset, we demonstrate notable decadal fluctuations in the number of haze days (HD) during winter in central eastern China, showing a decline since the mid-1980s. The leading mode of the wintertime HD features an increasing trend for 1959–2012 in eastern China, highly correlated with China’s gross domestic product (GDP) that represents increasing trend of pollutant emissions and to a lesser extent meteorological factors. The second mode shows decadal variations in central eastern China associated with Pacific Decadal Oscillation (PDO). Observations and numerical simulations suggest that Mongolia High and corresponding descending motion tend to be enhanced (weakened) in central eastern China during the positive (negative) phase of PDO. With PDO shifting towards a negative phase, the weakened Mongolia High and ascending anomalies make the air unstable and conduce to the spread of pollutants, leading to the decline in the wintertime HD over central eastern China since the mid-1980s. Based on above physical mechanisms, a linear model based on PDO and GDP metrics provided a good fit to the observed HD.