There are no well accepted mechanisms that can explain the annual frequency of tropical cyclones (TCs) both globally and in individual ocean basins. Recent studies using idealized models showed that the climatological frequency of TC genesis (TCG) is proportional to the Coriolis parameter associated with the intertropical convergence zone (ITCZ) position. In this study, we investigate the effect of the ITCZ position on TCG on the interannual time scale using observations over 1979-2020. Our results show that the TCG frequency is significantly correlated with the ITCZ position in the North Atlantic (NA) and Western North Pacific (WNP), with more TCG events in years when the ITCZ is further poleward. The ITCZ-TCG relationship in NA is dominated by TCG events in the tropics (0-20°N), while the relationship in WNP is due to TCs formed in the east sector (140-180°E). We further confirmed that the ENSO has little effect on the ITCZ-TCG relationship despite it can affects the ITCZ position and TCG frequency separately. In NA and WNP, a poleward shift of ITCZ is significantly associated with large-scale environment changes favoring TCG in the Main Development Region (MDR), However, the basin-wide TCG frequency has a weak relationship with the ITCZ in other ocean basins. We showed that a poleward ITCZ in the Eastern North Pacific and South Pacific favors TCG on the poleward flank of the MDR, whilst it suppresses TCG on the equatorward flank, leading to insignificant change in the basin-wide TCG frequency. In the South Indian Ocean, the ITCZ position has weak effect on TCG frequency due to the mixed influences of environmental conditions.

The two dominant patterns of the winter (December–February) intraseasonal surface air temperature (SAT) over central Asia is derived by empirical orthogonal function analysis, with the first (mode 1) featuring a regional monopole and the second (mode 2) featuring a northwest–southeast‐orientated dipole. Mode 1 is characterized with warmer (colder) Arctic and colder (warmer) Eurasia along with an anomalous high (low) over the Ural Mountains, while mode 2 is characterized with northwest–southeast dipole over Eurasia along with wave train‐like atmospheric circulation anomalies from the western Atlantic to Asia. Whether the two intraseasonal modes are modulated by lower‐boundary forcing is then investigated, and the results suggest that mode 1 is significantly modulated by sea ice concentration over the Greenland Sea, but by central‐Pacific ENSO for mode 2. Finally, the underlying mechanisms are diagnosed, and the results suggest that the diabatic heating related with decreased sea ice in Greenland Sea induce a positive height anomaly over Urals which favours the formation of Ural blocking and therefore tends to intensify the occurrence of mode 1. Also, central‐Pacific El Niño excites the Pacific–North American teleconnection, which alters North Atlantic subtropical jet extension, favours intensified energy conversion to intraseasonal wave train and subsequently intensifies the occurrence of mode 2. This study highlights the joint role of Arctic sea ice and the SST in the tropical central Pacific.