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The North Pacific Oscillation (NPO) is an important intrinsic atmospheric pattern over the North Pacific. Observations have shown that the boreal winter NPO is a crucial precursor to the El Niño-Southern Oscillation (ENSO), with many ENSO events being preceded by the NPO. It is therefore imperative to assess the ability of current coupled climate models to reproduce the relationship between winter NPO and the subsequent winter ENSO. Previous studies have shown that most coupled climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) underestimate the influence of winter NPO on the subsequent winter ENSO. Simulations from CMIP6, representing the latest generation of climate models, are now available. This study shows a remarkable improvement of the CMIP6 models in simulating the influence of winter NPO on the subsequent ENSO development compared to the CMIP5 models. This improvement is due to the improved air-sea interaction over the subtropical North Pacific in CMIP6. The enhanced air-sea interaction over the subtropical North Pacific promotes the equatorward propagation of the NPO-induced wind and SST anomalies, resulting in enhanced surface zonal wind anomalies over the tropical western Pacific, which further exert a stronger influence on the subsequent winter ENSO development by triggering the tropical Bjerknes positive air-sea interaction. The enhanced subtropical air-sea interaction is thought to be related to a southward shift of the North Pacific intertropical convergence zone in CMIP6 compared to CMIP5.

The sea ice concentration (SIC) over the Weddell Sea displays obvious intraseasonal variability during austral autumn with a dominant frequency of 5–20 days. The intraseasonal SIC variability is manifested as development of sea ice anomalies from the northeastern Antarctic Peninsula toward the central Weddell Sea. Rossby wave train associated with the internal atmospheric variability featuring circumglobal zonal wavenumber 4 pattern induces the development of anomalous surface winds and sea ice drifting, leading to the SIC anomalies directly. The thermodynamical processes associated with the intraseasonal SIC variability include the air temperature, the moisturizing of the lower troposphere, the latent and sensible heating, and the downwelling longwave radiation, which contribute to the variation of the local greenhouse effect over the Weddell Sea, and thus lead to the sea ice variation. The investigation of the intraseasonal SIC variability helps the understanding of sea‐ice‐atmosphere interaction over the Antarctic region. Plain Language Summary The variation of the Antarctic sea ice can modulate the atmospheric circulation over the Southern Hemisphere and play an important role in the sea‐ice‐atmosphere interaction. The intraseasonal sea ice concentration (SIC) variability over the Antarctic is more evident and with larger extent over the Weddell Sea during austral autumn, featuring a dominant frequency of 5–20 days. The evolution of the intraseasonal SIC variability manifests as SIC anomalies appearing over the northeastern Antarctic Peninsula and then moving eastward to the central Weddell Sea. It is controlled by the propagation of wave train around the Antarctic, which induces surface wind anomalies and sea ice movement. Besides, the air temperature, moisture, the latent and sensible heating, and the doweling longwave radiation can also contribute to the increase or melting of the sea ice through the modulation of the local greenhouse effect. Key Points The intraseasonal sea ice concentration (SIC) variability over the Weddell Sea manifests an evident frequency of 5–20 days in austral autumn Rossby wave train induces anomalous surface winds and sea ice drifting, leading to the intraseasonal SIC anomalies over the Weddell Sea Thermodynamical processes including moisture and longwave radiation can modulate local greenhouse effect and intraseasonal SIC anomalies

The North Pacific Oscillation (NPO), an important mode of atmospheric variability, is a crucial trigger for the development of El Niño-Southern Oscillation (ENSO) via the seasonal footprinting mechanism. How the NPO effect on ENSO changes in response to greenhouse warming remains unclear, however. Here, using climate model simulations under high-emission scenarios, we show that greenhouse warming leads to an enhanced influence of NPO on ENSO as is manifested by enhanced responses of winter sea surface temperature (SST), precipitation and wind anomalies in the equatorial Pacific to the preceding winter NPO. The strengthened NPO impact is also reflected in an increased frequency of NPO events that are followed by ENSO events. Warmer background SST enhances the wind-evaporation-SST feedback over the subtropical North Pacific due to a nonlinear SST-evaporation relationship. This strengthens the NPO-generated surface zonal wind anomalies over the equatorial western-central Pacific, which trigger ENSO. Increased impact of winter NPO on ENSO could enable prediction of interannual variability at longer leads.

The prediction of the tropical cyclone (TC) intensity remains a difficult issue. This study analyzes local instantaneous barotropic kinetic energy conversion in the lower troposphere in rapid intensifying (RI) and rapid decaying (RD) TCs over the western North Pacific (WNP) during June through November from 1979 to 2017. The kinetic energy conversion to the synoptic eddies is separated for climatological mean, interannual and intraseasonal flows. It is found that the intraseasonal cyclonic flows display a northwest‐southeast orientation in the RI TCs, but a circular feature in the RD TCs. Intraseasonal and climatological mean zonal flows contribute together to the positive kinetic energy conversion in the northwest quadrant of the RI TCs. Intraseasonal meridional flows induce positive (negative) kinetic energy conversion in the northeast (south) part of the RD TCs. The kinetic energy conversion associated with interannual flows is small for both the RI and RD TCs. Plain Language Summary The damage caused by the tropical cyclones (TCs) is closely related to their intensity. Revealing the factors of the intensification of the TCs may help to improve the skill of prediction of the TC intensity and reduce the damage of the TCs. From the energetic point of view, the intensification of the TCs requires the conversion of energy from the background flows. Here, we compare the barotropic kinetic energy conversion in the rapid intensifying (RI) and decaying (RD) TCs over the western North Pacific during June through November. Our analysis reveals that the intraseasonal flows have the largest contribution to both the RI and decaying TCs through the kinetic energy conversion to the synoptic scale eddies. The climatological mean flows have a secondary contribution to the RI TCs. The contribution of the interannual flows to the kinetic energy conversion is small for both the RI and RD TCs. Our results signify the importance of the configuration and magnitude of the background flows relative to the synoptic scale disturbances in the barotropic kinetic energy conversion for the TC intensity changes. Key Points Intraseasonal cyclonic flows feature a northwest‐southeast and circular distribution for rapid intensifying (RI) and decaying (RD) tropical cyclones (TCs), respectively Barotropic energy from intraseasonal and mean zonal flows contributes to the RI TCs Barotropic energy conversion from intraseasonal flows are opposite in northeast and south parts of the RD TCs

This work compares the contributions of synoptic, intraseasonal, and interannual components of large-scale parameters to tropical cyclone (TC) genesis over the North Indian Ocean (NIO) from April to December from 1979 to 2020. A composite analysis is employed with respect to TC genesis time and location. It is shown that most TCs occur when the total sea surface temperature (SST) is between 28 and 30 °C and SST anomalies in three time ranges are small (with the magnitude less than 0.2 °C). The TCs form mostly when the anomalies of vertical zonal wind shear are between −6 and 6 m s−1 and total vertical zonal wind shear falls within −12 and −3 m s−1, with the synoptic component being a positive contributor. The intraseasonal component of vorticity and convergence in the low level, vertical motion and specific humidity in the middle level, and convection contributes dominantly to the TC genesis. Synoptic-scale tropical disturbances obtain barotropic kinetic energy from the climatological mean and intraseasonal flows, with the former dominant in the southeastern sector, and the latter dominant in the northwestern sector. The contributions of the three temporal components of environmental factors are compared for TC genesis between the Arabian Sea (AS) and Bay of Bengal (BOB) and between the early season (April through June) and late season (September through December). The relative contributions of the three temporal components of factors are also compared for the TC formation among the NIO, northern tropical Atlantic Ocean (NTA), Northwestern Pacific (WNP), and Northeastern Pacific (ENP).

This study reveals a connection of summer–fall (JJASO) tropical cyclone (TC) genesis over the western North Pacific (WNP) to preceding boreal spring (MAM) North America snow cover (NASC). Sea surface temperature (SST) anomalies in the tropical central Pacific and subtropical eastern Pacific play a crucial role in relaying influence of the MAM NASC on the following JJASO WNP TC genesis frequency. The increased NASC leads to a decrease in upward sensible heat flux and the atmospheric cooling over the North America. The atmospheric cooling enhances the meridional thermal contrast and geopotential height gradient, which is favorable for the occurrence of lower-level westerly wind anomalies and positive precipitation anomalies over the tropical eastern Pacific. The lower-level northeasterly wind anomalies over the subtropical northeastern Pacific as a Gill-type atmospheric response to positive precipitation anomalies induce ocean surface cooling via the enhanced wind speed. A positive feedback between the northeasterly wind anomalies and negative SST anomalies leads to a westward extension of the easterly flows to the western Pacific. The easterly wind anomalies along with the negative specific humidity anomalies and negative lower-level vorticity anomalies, and enhanced vertical wind shear suppress the TC genesis over the WNP during JJASO.

This paper provides a systematic analysis of existing resource platforms, evaluating their advantages and drawbacks with respect to data privacy protection. To address the privacy and security risks associated with resource platform data, we propose a novel privacy protection algorithm based on chunking disorder. Our algorithm exchanges data within a specific range of chunk size for the position and combines the chunked data with the MD5 value in a differential way, thus ensuring data privacy. To ensure the security of the algorithm, we also discuss the importance of preventing client and server decompilation during its implementation. The findings of our experiments are as follows. Our proposed privacy-preserving algorithm is extremely secure and easy to implement. Our algorithm has a significant avalanche effect, maintaining values of 0.61–0.85, with information entropy being maintained at 4.5–4.9. This indicates that our algorithm is highly efficient without compromising data security. Furthermore, our algorithm has strong encryption and decryption time stability. The key length can be up to 594 bits, rendering it challenging to decrypt. Compared with the traditional DES algorithm, our algorithm has better security under the same conditions and approaches the levels of security offered by the AES and RC4 algorithms.

The impact of global warming on lightning flash rates remains relatively unknown. In this study, the South China Sea (SCS) and the surrounding areas within Southeast Asia were selected to examine the long‐term trend and future projection of lightning activity based on the currently longest satellite‐based lightning data set available and climate models. Our study revealed a reduction in the observed lightning flash rates around the SCS, with a linear trend of −0.11 fl km−2 yr−2 during 1996–2013. In contrast, the precipitation around the SCS exhibited an increasing trend and was negatively correlated with the local lightning flash rate. The sea surface temperature gradient over equatorial Pacific Ocean, latent heat flux over the equatorial Indian Ocean, local convective available potential energy, precipitation and aerosol changes collectively accounted for 82% of the variance in the lightning fluctuations over the SCS and Southeast Asia. Multiple linear regression proxies of lightning flash rates were constructed and applied to the climate models. The models indicated that lightning activity around the SCS is projected to intensify by 10% and 12% by the end of the 21st century under SSP245 and SSP370, respectively. Plain Language Summary The projection of future changes in lightning activity is uncertain owing to various factors, and different regions exhibit distinct trajectories. In this study, the focus was on the South China Sea (SCS) and Southeast Asia, and past variations in lightning activity was examined and used to predict future variations in lightning activity. Employing a multiple linear regression approach, we identified the large‐scale thermodynamic drivers and local environmental factors that influence lightning activity around the SCS. The research findings indicated a reduction in lightning activity over the past few decades over the SCS and Southeast Asia region. The simulation results indicate that in the future under ongoing global warming, regional lightning activity will intensify. Key Points Lightning activity and precipitation show opposing regional trends around the South China Sea (SCS) Remote thermodynamic and local environmental factors both contribute to the variability in lightning around the SCS Under future climate change scenarios, lightning activity around the SCS is projected to gradually increase

The hurricane, with maximum wind speed over 64 kts, is among the most terrible calamities over the northern Atlantic (NATL). Previous studies identified a poleward migration of tropical cyclone (TC) genesis over the Pacific Ocean, but the shift over the NATL is statistically insignificant. The present study detects a robust southward migration in the genesis latitude of NATL TCs that later reach hurricane strength after 1979, which is consistent with a growth in hurricane frequency in the southern part (10°-20°N) of NATL. This increasing trend of hurricane frequency is intimately attributable to the decreasing vertical shear of zonal wind, resulting from a decreasing north-south temperature gradient. The reduced north-south temperature gradient is primarily caused by greater warming trend in tropospheric temperature in the subtropics, driven by intensified static stability. The present research suggests a potential increase in the hazards confronted by low-latitude islands and coastal nations in Northern America.

Based on the ERA-40 reanalysis data from the European Centre for Medium-Range Weather Forecasts and the output of ECHAM5/MPI-OM, this study investigated the interactions between the quasi-stationary planetary wave （SPW） and mean flow, and their responses to E1 Nifio-Southern Oscillation （ENSO） events in the northern hemispheric stratosphere. Results show that the activity of SPW is the strongest in winter, when the SPW propagates along the polar waveguide into the stratosphere and along the low-latitude waveguide to the subtropical tropopause. The analysis of three dimensional SPW structure indicates that the main sources of SPW activity are located over the Eurasian continent and the North Pacific north of 45°N. On the one hand, the two waveguides of the SPW reflect the influence of mean flow on the propagation of the SPW. On the other hand, the upward propagating SPW can interact with the stratospheric mean flow, leading to deceleration of the zonal mean westerly. Furthermore, the SPW exhibits clear responses to ENSO events. During E1 Nifio winters, the SPW in the strat- osphere tends to propagate more upward and poleward. Its interactions with mean flow can induce a dipole pattern in zonal mean zonal winds, with accelerated westerly winds at low-middle latitudes and decelerated westerly winds at high latitudes. The ECHAM5/MPI-OM model reproduces the climatology of the SPW well. Although the simulated SPW is slightly weaker than the observations in the stratosphere, the model＇s performance has significant improvements compared with other GCMs used in previous studies. However, there are still some problems in the responses of the SPW to ENSO in the model. Although the model reproduces the responses of both the amplitude and the SPW-mean flow interactions to ENSO well in the troposphere, the stratospheric responses are quite weak. Therefore, further studies are needed to improve the simulation of the stratospheric atmospheric circulation and related dynamical processes.