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This study aimed to explore the predictability of the most long‐lived tropical cyclone (TC) Freddy in 2023 while it traversed westward across the southern tropical Indian Ocean during the first 18 days of its existence. Global ensemble forecasts revealed southward track deflection and intensity underestimation of Freddy. We identified three key factors contributing to the limited predictability of Freddy, which are associated with the Mascarene High, Storm Dingani, and Freddy itself. The large track errors of Freddy can be attributed to the underestimated strength of the Mascarene High, the more northeastern position of Dingani, and the presence of excessively large or small sizes of Freddy. These findings were further validated through a high‐resolution regional model. Specifically, Freddy's track and intensity most closely matched the observations when these three factors were most closely represented. It underscores the pivotal role played by the interaction between TCs and multi‐scale systems in TC forecasts. Plain Language Summary: In 2023, Storm Freddy emerged as the most long‐lived tropical cyclone (TC) in record, lasting 35 days over the southern tropical Indian Ocean and spanning both weather and sub‐seasonal to seasonal time ranges. The primary objective of this study is to understand the factors contributing to the poor predictability of Freddy in forecasts spanning over 2 weeks. This holds significant importance as our understanding about the ability of the numerical models to predict long‐lived TCs remains limited. Using over 7,000 global ensemble forecasts from five global Numerical Weather Prediction (NWP) centers and a high‐resolution regional model, we identified three key factors contributing to the limited predictability of Freddy: the strength of the Mascarene High, the position of Storm Dingani (2023), and the size of Freddy. In large track‐error results of the global forecasts and regional simulations for Freddy, the strength of the Mascarene High was underestimated, Dingani was located further northeast, and Freddy was either too large or too small. Our investigation emphasizes the crucial role played by the interaction between the TC and multi‐scale systems in TC forecasts. This is meaningful for the improvement of Numerical Weather Prediction models to deal with extreme TC events in the future. Key Points: Due to the long lifespan of Storm Freddy, many forecasting challenges across several numerical models aroseThe limited predictability of Freddy was related to the underestimated Mascarene High and the more northeastern position of Storm DinganiThe inaccurately forecasted size of Freddy, whether excessively large or small, also contributed to the large track errors [ABSTRACT FROM AUTHOR]

A record-breaking precipitation event occurred in the Henan province of China in July 2021 (217HP). To identify the moisture source of the event, ensemble experiments with 120 members were conducted in this study. Results show that the precipitable water during this extreme event was primarily contributed by the low-level southeasterly (LLSE) water vapor transport. The LLSE was largely enhanced by the pressure gradient force maintained by the western Pacific subtropical high and further amplified by the latent heat release in the rainfall system over Henan. The positive moisture advection by the LLSE and evaporative water occurred below 950 hPa and was redistributed into higher levels by the LLSE jet-enhanced subgrid vertical turbulent transport. As a result, the combination of the enhanced LLSE centered around 950 hPa and the increase of moisture below 850 hPa were the main drivers for the continuous strengthening of LLSE moisture transport, with the former playing the dominant role. It is also found that not only the presence but also the intensity of the LLSE jet were important for reproducing the extreme rainfall. The impact of binary tropical cyclones In-Fa and Cempaka on the low-level moisture transport was also examined. We found that In-Fa (2021) presented an uncertain impact on 217HP, while Cempaka (2021) was found to be unfavorable for 217HP. Different from the LLSE water vapor transport, Cempaka mainly acted to weaken the southwesterly wind to the southwest of Henan by reducing the pressure gradient and impeding the water vapor transport toward Henan. [ABSTRACT FROM AUTHOR]

This study investigates the evolution of tropopause layer cooling (TLC) in an idealized tropical cyclone (TC) as well as the physical mechanism for its formation throughout its lifetime. TLC development is closely related to the intensity change of the TC. The TLC within the inner core of a TC coincides with the occurrence of the TC warm core, whereas the enhancement of the TLC precedes the strengthening of the warm core and the intensification of the TC. This phenomenon suggests that the TLC could be a valuable signal for predicting TC intensity and intensity change. After the onset of rapid intensification, the TLC continues to enhance until it is replaced by the warm core in the inner core region, and it expands to the outer core area and forms a cold ring above the TC outflow layer. The budget analyses of the azimuthal mean potential temperature indicate that advection plays a leading role during all stages of the TLC evolution. Prior to and during the rapid intensification stages of a TC, advection (due to eddy motion) contributes to a cooling of the upper layer above the TC center. This upper‐level cooling is assumed to be related to the uplift caused by overshooting and convection within the inner core. However, the advection process caused by the azimuthal vertical motion dominated the broad cooling across the whole TLC area. Plain Language Summary: Observations and numerical simulations show that there is typically a cold anomaly above the TC warm core. This cooling can work with the warm core to reduce the upper‐tropospheric stability and affect the water vapor and momentum transport between the TC and the stratosphere. However, little is known about how the cold anomaly evolves during the life cycle of a TC and how it can be related to changes in TC intensity. This study examines the evolution of the cold anomaly throughout the lifetime of a TC with an idealized TC simulation. The cold anomaly emerges at the TC center before rapid intensification starts and continues to enhance during TC development. It moves radially and forms a cold ring around the TC until the mature stage. The advection, specifically the vertical mean motion, dominates the generation of the TLC, but the advection due to eddy motions is responsible for the cold anomaly near the center. Our findings demonstrate the importance of tropopause layer cooling on TC structure and intensity changes and indicate the necessity of additional observations of this cold anomaly to improve TC predictions. Key Points: The cooling tendency in the tropopause layer enhances continuously during the preintensification and rapid intensification stages of tropical cyclone (TC)The adiabatic uplift caused by overshooting convection can cool the upper layer in the TC center through azimuthal‐eddy advectionThe broad ring of the cold anomaly above the TC outflow layer is related to adiabatic cooling through the azimuthal mean vertical motion [ABSTRACT FROM AUTHOR]

The rainfall distribution in a tropical cyclone (TC) is affected by many factors/processes. Most of previous studies have focused on individual TCs. Little is known about the rainfall distribution in binary TCs. This study examines the rainfall distribution in binary TCs over the western North Pacific based on the observational data. When two TCs become nearby, the asymmetric component of rainfall shows an increasing trend with rainfall significantly suppressed in Quadrant IV of the TC located to the west when orienting the two TCs in the west‐east direction. The suppression becomes remarkable once the separation distance between the two TCs is within about 2,050 km. Furthermore, the convective activity in one TC is related to the deep‐layer vertical wind shear (VWS) from its companion. Rainfall is enhanced downshear‐left in a TC, consistent with a single TC embedded in an environmental VWS as found in previous studies. Plain Language Summary: The rainfall distribution in each tropical cyclone (TC) of binary‐TC systems may be more complicated than that in a single TC. Whether the rainfalls of binary TCs have some special features has not been studied before. This observational study examines the rainfall distribution in binary TCs over the western North Pacific during 2001–2020. The results show that the asymmetric component of TC rainfalls strengthened with the decreasing of the separation distance between the two TCs. If orient binary TCs in the west‐east direction, the rainfalls of the western TC were distinctly weakened in its Quadrant IV. The suppression effect cannot be neglected within 2,050‐km separation distance between binary TCs. Composite analyses indicate that the asymmetric rainfalls in one of the binary TCs were related to the deep‐layer vertical wind shear induced by its companion. The consistent pattern of rainfall asymmetry indicates a highly predictable component of rainfall distribution at vortex‐scale in binary TCs and can help improve the precipitation forecast of binary TCs. Key Points: The rainfall asymmetry increases with the decreasing separation distance between binary tropical cyclones (TCs)If the two TCs are oriented west‐east and within about 2,050 km, rainfall in the western TC is suppressed in its Quadrant IVThe asymmetric convective activity in one TC can be explained by the deep‐layer vertical wind shear from its companion [ABSTRACT FROM AUTHOR]

No tropical cyclone (TC) formed over the western North Pacific (WNP) in July 2020, which is record‐breaking. Some recent studies suggested that this extreme event was mainly caused by the strong WNP subtropical high (WNPSH) in July 2020, which might not be the only reason. In this study, results from statistical and composite analyses indicate that the strong WNPSH, the strong South Asian high, the westward extended tropical upper‐tropospheric trough, and the weak South Asian summer monsoon are all detrimental to TC genesis over the WNP and might contribute to the absence of TCs in July 2020. Results from sensitivity experiments using a regional atmospheric model that can resolve TCs further demonstrate that it was the collective effect, not any of the individual large‐scale circulation anomalies, that induced the extremely unfavorable conditions for TC genesis and thus led to the record‐breaking inactive TC month. Plain Language Summary: Tropical cyclones (TCs) become more active during the typhoon season (from July to September) over the western North Pacific (WNP). However, it is an exception in the records that no TC formed over the WNP in July 2020. Some recent studies suggest that this extreme event was mainly caused by the strong WNP subtropical high (WNPSH) in July 2020. This study identified four large‐scale circulation anomalies that are detrimental to TC genesis over the WNP and might contribute to this extremely inactive TC event, including the strong WNPSH, the strong South Asian high (SAH), the westward extended tropical upper‐tropospheric trough, and the weak South Asian summer monsoon (SASM). The strong WNPSH reduced the mid‐level moisture and the low‐level vorticity; the strong SAH and the westward shift of the tropical upper‐tropospheric trough increased the deep‐level vertical wind shear; and the weak SASM could not provide sufficient low‐level relative vorticity. It is the combined effect, not any of the individual large‐scale circulation anomalies, that induced the extremely unfavorable conditions for TC genesis and led to the absence of TCs over the WNP in July 2020. Key Points: No tropical cyclone (TC) formed over the western North Pacific (WNP) in July 2020, an extreme month that has never occurred in historyIt is due to the combination of anomalies in the WNP subtropical high, the South Asian high, the South Asian summer monsoon, and the tropical upper‐tropospheric troughTC‐resolving numerical experiments demonstrate the detrimental contributions of all the four large‐scale atmospheric circulations [ABSTRACT FROM AUTHOR]

A high crystalline quality of SiGe fin with an Si-rich composition area using the replacement fin processing is systematically demonstrated in this paper. The fin replacement process based on a standard FinFET process is developed. A width of less than 20-nm SiGe fin without obvious defect impact both in the direction across the fin and in the direction along the fin is verified by using the high angle annular dark field scanning transmission electron microscopy and the scanning moiré fringe imaging technique. Moreover, the SiGe composition is inhomogenous in the width of the fin. This is induced by the formation of {111} facets. Due to the atomic density of the {111} facets being higher, the epitaxial growth in the direction perpendicular to these facets is slower than in the direction perpendicular to {001}. The Ge incorporation is then higher on the {111} facets than on the {001} facets. So, an Si-rich area is observed in the central area and on the bottom of SiGe fin. [ABSTRACT FROM AUTHOR]

This paper reports on a dynamical initialization scheme for binary vortices (BVDI) that was developed to improve the initial conditions supplied to the models used to forecast binary tropical cyclones (TCs). For binary TCs, one TC can be regarded as the environment for the other TC's development. Based on the dynamical initialization scheme for a single vortex (SVDI), a specified multistep iteration of SVDI was introduced in the BVDI scheme to ensure that each TC develops under conditions of realistic binary vortices interaction during the 6-h cycle run. In the BVDI scheme, each TC is initialized twice within a continuously adjusted environmental flow. Four clusters of forecast simulations with different initial conditions were run for 11 pairs of binary TCs over the northwest Pacific. The forecasts of binary TCs by the BVDI scheme reduced the position and intensity errors associated with the forecast TCs by 35.2% and 56.6%, respectively, compared with those without initialization, and also performed better than the direct extension of the SVDI scheme to binary TCs. The representation of binary vortices interaction will need to be improved for initialization and future forecasts of binary TCs. [ABSTRACT FROM AUTHOR]