Contributions of Different Time-Scale Variations to Tropical Cyclogenesis over the Western North Pacific

Intl Journal of Climatology

Zhan

2019

Self Cite

A distinct inter‐decadal increase of tropical cyclone (TC) frequency occurred over the South China Sea (SCS) around the mid‐1990s. Previous studies linked this TC frequency increase to changes in seasonal mean background fields and in the intensity of intra‐seasonal oscillations according to regional and seasonal mean fields. The present study compares the contributions of environmental factors on different timescales to inter‐decadal change of the SCS TC frequency from a local and instantaneous perspective. It is shown that the intra‐seasonal variations of lower‐level vorticity, mid‐level specific humidity, and vertical motion have a dominant contribution to the SCS TC genesis during both 1979–1993 and 1994–2002. The inter‐annual anomalies of sea surface temperature (SST), outgoing longwave radiation (OLR), and vertical motion display an increase of favourable state near TC genesis regions at the mid‐1990s. The intra‐seasonal components of favourable OLR and vertical motion anomalies are larger in the latter period than in the former period. The synoptic components of favourable lower‐level vorticity, vertical wind shear, and mid‐level specific humidity anomalies increase from the former period to the latter period. The present study shows that the contributions of environmental factors to the SCS TC frequency have increased on different timescales around the mid‐1990s. The results suggest that this inter‐decadal increase of TC frequency may include both effects of dynamical‐driven changes and stochastic processes.

Section: Methodsmentioning

confidence: 97%

Section: Contributions Of Different Timescale Variations Of Environmementioning

confidence: 99%

Section: Contributions Of Different Timescale Variations Of Environmementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Re‐examining the decadal change of tropical cyclogenesis over the South China Sea around the mid‐1990s

Intl Journal of Climatology

Zhan

2019

Self Cite

Relative contributions of environmental factors on different time scales to tropical cyclogenesis over the eastern North Pacific

Atmospheric Science Letters

Feng

et al. 2021

Self Cite

The present study investigates relative contributions of large-scale environmental factors on interannual, intraseasonal, and synoptic time scales to tropical cyclone (TC) genesis over the eastern North Pacific (ENP) during TC seasons of 1979-2013 from the perspective of TC genesis time and position. Conditional sorting displays that the synoptic component is more important in the contribution of lower-level vorticity and mid-level specific humidity to TC genesis compared to interannual and intraseasonal components. The convection contributes to TC genesis mainly through synoptic and intraseasonal components. Synoptic-scale tropical disturbances mainly obtain barotropic eddy energy from climatological mean flows. TCs appear most frequently when vertical wind shear anomalies are between 0 and 3 m s −1 , in which interannual and intraseasonal westerly wind anomalies make a positive contribution due to climatological easterly wind shear. When total SST exceeds 28 C, the interannual component of sea surface temperature (SST) is positive, and then it has a positive contribution to TC genesis. In addition, there are notable differences of relative contributions of different time scale components of large-scale factors among the ENP, northern Atlantic Ocean, and western North Pacific.

Northwestwards shift of tropical cyclone genesis position during autumn over the western North Pacific after the late 1990s

Intl Journal of Climatology

Liu

et al. 2019

Self Cite

Previous study has suggested a northwestwards shift of tropical cyclone (TC) genesis position during autumn over the western North Pacific (WNP) after the late 1990s. This study replenishes two mechanisms to explain this inter‐decadal change in the WNP TC genesis position. The first mechanism is related to the mean state change. According to observational analysis and numerical simulations with the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric general circulation model, a La Niña‐type Pacific sea surface temperature (SST) change and the northern Atlantic Ocean warming in the late 1990s cause a dipole pattern of lower‐level circulation change, with cyclone over the northwestern WNP and anticyclone over the southeastern WNP. This pattern is favourable for more TC genesis in the northwestern WNP. The sensitivity experiments show that the contribution from the Pacific Ocean is larger than that from the northern Atlantic Ocean. The second mechanism is related to the change in the intra‐seasonal oscillation intensity, particularly the quasi‐biweekly variation. The activity of intra‐seasonal oscillations over the southeastern WNP shows a decadal decrease around the late 1990s. Meantime, when the intra‐seasonal oscillations with tilted structure move northwestwards, they provide a favourable condition for TC genesis to be located more northwestwards after the late 1990s.