Modulation of North Pacific and North Atlantic tropical cyclones by tropical trans-basin variability and ENSO during May-October

This study highlights the distinct modulation of May-October tropical cyclones (TCs) in the western North Pacific (WNP), eastern North Pacific (ENP) and North Atlantic (NATL) basins by tropical trans-basin variability (TBV) and ENSO. The pure TBV significantly modulates total TC counts in all three basins, with more TCs in the WNP and ENP and fewer TCs in the NATL during warm TBV years and fewer TCs in the WNP and ENP and more TCs in the NATL during cold TBV years. By contrast, the pure ENSO signal shows no impact on total TC count over any of the three basins. These results are consistent with changes in large scale factors associated with TBV and ENSO. Low-level relative vorticity (VOR) is an important driver of WNP TC genesis frequency, with broad agreement between the observed spatial distribution of TC genesis and TBV/ENSO-associated VOR anomalies. TBV significantly affects ENP TC frequency due to changes in basin wide vertical wind shear and sea surface temperatures, while the modulation in TC frequency by ENSO is primarily caused by a north-south dipole modulation of large-scale atmospheric and oceanic factors. The pure TBV-related low-level VOR changes appear to be the most important factor modulating NATL TC frequency. Changes in large-scale factors compare well with the budget of synoptic-scale eddy kinetic energy. Possible physical processes associated with pure TBV and pure ENSO that modulate TC frequency are further discussed. This study contributes to the understanding of TC inter-annual variability and could thus be helpful for seasonal TC forecasting.

A pixel space method for testing dipole modulation in the CMB polarization

ABSTRACT We introduce a pixel space method to detect dipole modulation or hemispherical power asymmetry in the cosmic microwave background (CMB) polarization. The method relies on the use of squared total polarized flux whose ensemble average picks up a dipole due to the dipole modulation in the CMB polarization. The method is useful since it can be easily applied to partial sky. We define several statistics to characterize the amplitude of the detected signal. Through simulations, we show that the method can be used to reliably extract the signal at a 2.7σ level or higher in future CORE-like missions, assuming that the signal is present in the CMB polarization at the level detected by the Planck mission in the CMB temperature. An application of the method to the 2018 Planck data does not detect a significant effect, when taking into account the presence of correlated detector noise and residual systematics in the data. Using the Full Focal Plane 10, we find the presence of a very strong bias that might be masking any real effect.