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Abstract A novel recursive cascaded full‐resolution residual network (RCFRR‐Net) for abdominal four‐dimensional computed tomography (4D‐CT) image registration was proposed. The entire network was end‐to‐end and trained in the unsupervised approach, which meant that the deformation vector field, which presented the ground truth, was not needed during training. The network was designed by cascading three full‐resolution residual subnetworks with different architectures. The training loss consisted of the image similarity loss and the deformation vector field regularization loss, which were calculated based on the final warped image and the fixed image, allowing all cascades to be trained jointly and perform the progressive registration cooperatively. Extensive network testing was conducted using diverse datasets, including an internal 4D‐CT dataset, a public DIRLAB 4D‐CT dataset, and a 4D cone‐beam CT (4D‐CBCT) dataset. Compared with the iteration‐based demon method and two deep learning‐based methods (VoxelMorph and recursive cascaded network), the RCFRR‐Net achieved consistent and significant gains, which demonstrated that the proposed method had superior performance and generalization capability in medical image registration. The proposed RCFRR‐Net was a promising tool for various clinical applications.

Abstract 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.

Abstract When passing by Taiwan, Typhoon Meranti (2016) was deflected northwards and shrank on infrared images, while its intensity maintained above 50 m⋅s–1 with the radius of maximum wind (RMW) smaller than 30 km. In this paper, satellite and ground‐based dual‐Doppler data were adopted to document Meranti's inner core evolution after its interaction with Taiwan's topography. It was found that the eyewall of Meranti was highly asymmetric on radar reflectivity with maximum on the down motion left side during its landfalling stage in Taiwan Strait, whereas the environmental vertical shear (about 3 m⋅s–1) was not favorable for asymmetry of this strength. As Meranti was very close to Taiwan's southern tip when passing by, its deep convection distribution, especially part on the down motion right side, was impaired by the topography of Central Mountain Range, thus contributed to this asymmetry. The eyewall at 1645 UTC was examined in detail, and it was found that the primary circulation with weaker azimuth perturbations remained intact at this time, while vertical circulation differed with direction. Besides, there was a low level northeast‐southwest flow through the eye, same as the direction of Taiwan Strait. Perhaps this radial inflow, along with the primary circulation, had contributed to the maintenance of asymmetry in reflectivity, so the eyewall did not recover in the Strait despite the weak wind shear. In addition, stronger storm‐relative wind asymmetry in the mid‐troposphere was observed. This wind asymmetry was in favor of track deflection, so was the diabatic heating associated the rainfall asymmetry. The channel wind, along with downslope wind from Taiwan, may help to maintain the intensity of Meranti and the smaller RMW, which needed further investigation with high resolution numerical models.