Response of the western North Pacific subtropical ocean to the slow-moving super typhoon Nanmadol

Based on in-situ observation,satellite and reanalysis data,responses of the western North Pacific subtropical ocean(WNPSO)to the slow-moving category 5 super typhoon Nanmadol in 2011 are analyzed.The dynamical response is dominated by near-inertial currents and Ekman currents with maximum amplitude of 0.39m/s and 0.15m/s,respectively.The near-inertial currents concentrated around 100m below the sea surface and had an e-folding timescale of 4 days.The near-inertial energy propagated both upward and downward,and the vertical phase speed and wavelength were estimated to be 5m/h and 175m,respectively.The frequency of the near-inertial currents was blue-shifted near the surface and redshifted in ocean interior which may relate to wave propagation and/or background vorticity.The resultant surface cooling reaches-4.35℃ and happens when translation speed of Nanmadol is smaller than 3.0m/s.When Nanmadol reaches super typhoon intensity,the cooling is less than 3.0℃ suggesting that the typhoon translation speed plays important roles as well as typhoon intensity in surface cooling.Upwelling induced by the slow-moving typhoon wind leads to typhoon track confined cooling area and the right-hand bias of cooling is slight.The mixed layer cooling and thermocline warming are induced by wind-generated upwelling and vertical entrainment.Vertical entrainment also led to mixed layer salinity increase and thermocline salinity decrease,however,mixed layer salinity decrease occurs at certain stations as well.Our results suggest that typhoon translation speed is a vital factor responsible for the oceanic thermohaline and dynamical responses,and the small Mach number(slow typhoon translation speed)facilitate development of Ekman current and upwelling.

Numerical Simulation of the Relationship between the Anomaly of Subtropical High over East Asia and the Convective Activities in the Western Tropical Pacific

In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.

Tracking typhoon-generated swell in the western North Pacific Ocean using satellite altimetry

This paper proposes a scheme for detecting the swell decay of a moving typhoon. We considered a typhoon that was neither far from a point source nor had a belt-like homogenous source,as previously studied. We tracked the swell close to the source during a typhoon in the western North Pacific Ocean. We used wind speed and significant wave height data derived from the Geophysical Data Record of the Jason-1 altimeter and the best-track information of the typhoon from the China Meteorological Administration tropical cyclone database. We selected three specific cases to reveal the decay characteristics of the swell generated by a moving typhoon. Based on an altimeter-based typhoon swell identification scheme and the dispersion relationship for deep water,we relocated the swell source for each altimeter measurement. The subsequent statistical decay coefficient was comparable to previous studies,and effectively depicted the swell propagation conditions induced by the typhoon. We hope that our results provide a new understanding of the characteristics and wave energy budget of the North Pacific Ocean,and significantly contribute to wave modeling in this region.

Typhoon frequency and intensity across the Western Pacific Ocean north of the Equator, 1951 – 2014

Disturbance has been a repeated theme in ecology in recent decades,yet incorporating its frequency and pattern at broad spatial scales into ecological analyses has been difficult-rather,most environmental datasets used in broad-extent analyses represent average conditions.We present a detailed dataset summarizing the frequency(i.e.,number of typhoons)and intensity(average and maximum windspeeds)of typhoons across the Western Pacific north of the Equator,based on data characterizing tracks for 1673 typhoons from the Japan Meteorological Center.The data presented are aggregated and resampled to 0.2°(~22 km at the Equator)spatial resolution;temporal coverage extends 1951-2014.We also present data specifically for prior to 1980 and after 1999,to respond to questions related to climate change,although no major changes were evident between the time periods.

Impact of the Thermal State of the Tropical Western Pacific on Onset Date and Process of the South China Sea Summer Monsoon

Since the early or late onset of the South China Sea summer monsoon （SCSM） has a large impact on summer monsoon rainfall in East Asia, the mechanism and process of early or late onset of the SCSM are an worthy issue to study. In this paper, the results analyzed by using the observed data show that the onset date and process of the SCSM are closely associated with the thermal state of the tropical western Pacific in spring. When the tropical western Pacific is in a warming state in spring, the western Pacific subtropical high shifts eastward, and twin cyclones are early caused over the Bay of Bengal and Sumatra before the SCSM onset. In this case, the cyclonic circulation located over the Bay of Bengal can be early intensified and become into a strong trough. Thus, the westerly flow and convective activity can be intensified over Sumatra, the Indo-China Peninsula and the South China Sea （SCS） in mid-May. This leads to early onset of the SCSM. In contrast, when the tropical western Pacific is in a cooling state, the western Pacific subtropical high anomalously shifts westward, the twin cyclones located over the equatorial eastern Indian Ocean and Sumatra are weakened, and the twin anomaly anticyclones appear over these regions from late April to mid-May. Thus, the westerly flow and convective activity cannot be early intensified over the Indo-China Peninsula and the SCS. Only when the western Pacific subtropical high moves eastward, the weak trough located over the Bay of Bengal can be intensified and become into a strong trough, the strong southwesterly wind and convective activity can be intensified over the Indo-China Peninsula and the SCS in late May. Thus, this leads to late onset of the SCSM. Moreover, in this paper, the influencing mechanism of the thermal state of the tropical western Pacific on the SCSM onset is discussed further from the Walker circulation anomalies in the different thermal states of the tropical western Pacific.

Influence of Indian Ocean Dipole on Tropical Cyclone Activity over Western North Pacific in Boreal Autumn

In this study, we investigated the influence of the Indian Ocean Dipole (IOD) on the interannual variability of tropical cyclone (TC) activity over the western North Pacific (WNP) during autumn (September November) from 1961 2015. We found the number of TCs making landfall in China to be significantly negatively correlated with the IOD index, which can be attributed to shifts in the location of TC formation together with the abnormal steering flow at 500 hPa. During negative IOD autumns, TC genesis regions move obviously westward due to the westward retreat of the WNP monsoon trough. The TC activity is remarkably enhanced near South China coastal areas, which is due to a contiguous 500-hPa subtropical ridge. In contrast, during positive IOD autumns, TC genesis positions obviously shift eastward and more TCs tend to exhibit recurvature around 130 E or a westward path south of 15 N led by an equatorward movement of the 500-hPa subtropical ridge with a break near 125 E. In our examination of large-scale circula- tion, we found a pair of equator-symmetric anticyclones in the lower troposphere resulting from variations in the large-scale Walker circulation induced by the anomalous sea surface temperature (SST) associated with a positive IOD. The resulting Philippines anti- cyclonic anomalies are closely related to the variability of the monsoon trough over the WNP region. Furthermore, the variations in the steering flow can be explained by the suppressed (enhanced) convective activities around the Philippines and the weakened (strengthened) local meridional circulation over East Asia in positive (negative) IOD years.

Geology and mineralization of the Hongqiling large magmatic nickel-copper-cobalt deposit(22×10^(4)t)in Jilin Province,China:A review

The Hongqiling large nickel-copper-cobalt deposit(hereafter referred to as the Hongqiling deposit),a typical mafic-ultramafic copper-nickel deposit in China,boasts proven Ni(Ni)resources of approximately 22×10^(4)t,associated copper resources of 2×10^(4)t,and associated cobalt(Co)resources of 0.5×10^(4)t,with Ni reserves ranking 10th among China's magmatic nickel deposits.Geotectonically,the Hongqiling deposit is situated in the superimposed zone between the Xing'an-Mongolian orogenic belt and the circum-Western Pacific's active continental margin belt.Its ore-bearing plutons occur within the metamorphic rocks of the Ordovician Hulan Group,with the emplacement of plutons and the locations of orebodies governed by the deep-seated Huifahe fault and its secondary NW-trending Fujia-Hejiagou-Beixinglong-Changsheng fault zone.In the deposit,the rock assemblages of ore-bearing plutons predominantly encompass gabbro-pyroxenite-olivine pyroxenite-pyroxene peridotite(pluton No.1)and norite-orthopyroxenite-harzburgite(pluton No.7),with ore-bearing lithofacies consisting primarily of olivine pyroxenite and pyroxenite facies.The Hongqiling deposit hosts stratoid,overhanging lentoid,veined,and pure-sulfide veined orebodies.Its ores principally contain metallic minerals including pyrrhotite,pentlandite,chalcopyrite,violarite,and pyrite.Despite unidentified magma sources of ore-bearing mafic-ultramafic rocks,it is roughly accepted that the magmatic evolution in the Hongqiling deposit primarily involved fractional crystallization and crustal contamination.The ore-forming materials were primarily derived from the upper mantle,mixed with minor crustal materials.The ore-bearing mafic-ultramafic rocks in the deposit,primarily emplaced during the Indosinian(208-239 Ma),were formed in an intense extension setting followed by the collisional orogeny between the North China Plate and the Songnen-Zhangguangcai Range Block during the Middle-Late Triassic.From the perspective of the metallogenic geological setting,surrounding rocks,ore-controlling structures,and rock assemblages,this study identified one favorable condition and seven significant indicators for prospecting for Hongqiling-type nickel deposits and developed a prospecting model of the Hongqiling deposit.These serve as valuable references for exploring similar nickel deposits in the region,as well as the deep parts and margins of the Hongqiling deposit.

A METHOD OF ESTIMATING TYPHOON CENTRAL WIND BASED ON SEA LEVEL PRESSURE OF THE TYPHOON YEARBOOK OF CHINA

Based on the Typhoon Yearbook data(1980-2000),some wind-pressure fitting relationships were established for different typhoon intensity at the different latitudes of the western North Pacific.As shown in validations with the 2001-2005 data,the relationships(namely,those between minimum sea level pressure(SLP) and maximum sustained wind near a typhoon center) are stable.They may be applied to correct the overestimated typhoon wind speeds in earlier years(1950-1979).Statistical analysis showed that the stronger the typhoon,the more stable this wind-pressure relationship is.Moreover,it is more stable at the lower latitude belt(10°N-30°N).On the basis of this result,a methodology of correcting typhoon's wind speeds and frequency in these years was put forward,and the climatological series were reconstructed of yearly total typhoon frequencies over the western North Pacific in 1950-1979 and indices were determined of destructive power of typhoons in the offshore regions of China.

Role of the 10–20-Day Oscillation in Sustained Rainstorms over Hainan,China in October 2010

Hainan,an island province of China in the northern South China Sea,experienced two sustained rainstorms in October 2010,which were the most severe autumn rainstorms of the past 60 years.From August to October 2010,the most dominant signal of Hainan rainfall was the 10-20-day oscillation.This paper examines the roles of the 10-20-day oscillation in the convective activity and atmospheric circulation during the rainstorms of October 2010 over Hainan.During both rainstorms,Hainan was near the center of convective activity and under the influence of a lower-troposphere cyclonic circulation.The convective center was initiated in the west-central tropical Indian Ocean several days prior to the rainstorm in Hainan.The convective center first propagated eastward to the maritime continent,accompanied by the cyclonic circulation,and then moved northward to the northern South China Sea and South China,causing the rainstorms over Hainan.In addition,the westward propagation of convection from the tropical western Pacific to the southern South China Sea,as well as the propagation farther northward,intensified the convective activity over the northern South China Sea and South China during the first rainstorm.

Will typhoon over the western North Pacific be more frequent in the Blue Arctic conditions?

How would typhoon activity over the western North Pacific change for various scenarios of future global warming?Using the model projections of the Coupled Model Intercomparison Project phase 3(CMIP 3)under the SRES A1B scenario,we generated summer(September)ice-free Arctic conditions,also referred to as Blue Arctic conditions,and then used the corresponding monthly sea surface temperature(SST)and a set of CO2concentrations to drive an AGCM model to simulate the resulting changes in background conditions affecting typhoon activity over the western North Pacific.Our results show that,during typhoon season(June to October),atmospheric and ocean circulations over the western North Pacific would be significantly different from the present circulations.Changes in the vertical shear of zonal wind and outgoing longwave radiation(OLR)in the western North Pacific are favorable for westward and northward shift,respectively,of the location of typhoon genesis.Moreover,changes in the above fields over the key area may be conducive to less frequent typhoons.In addition,the tropical cyclone genesis potential index(GPI)over the western North Pacific would decrease(increase)east(west)of 150°E(140°E).

SOME SPECIAL CHARACTERISTICS OF TRACK AND INTENSITY OF TYPHOONS OVER THE WESTERN NORTH PACIFIC

Joint Typhoon Warning Center(JTWC) Best Track data from 1995 to 2014 are processed to examine some specific patterns and trends shown by Typhoons over the Western North Pacific. With a multivariate dataset of 588 TC cases in hand, we carry out a sub-domain analysis by dividing the Western North Pacific region into domains of 2°x2° and find the preferred regions of genesis, favourable direction of movement, steep recurvature, rapid intensification, and rapid decay. The region from longitude 132°E to 134°E and latitude 16°N to 18°N showed the highest number of cases(19) for rapid intensification(RI) and a general pattern is found that the RI systems occurred mostly in the later half of the year with a negative Pacific Decadal Oscillation(PDO) index. Similarly, the domain from longitude 114°E to 116°E and latitude 26°N to 28°N had the highest probability of 0.857 for rapid decay. The probabilities of recurvature for each sub-domain were calculated for angles 30°, 45°, 60°, 90°, 120° and 150°. The sub-domain around longitude 118°E and latitude 12°N had the steepest recurve of 168.69°. It also had a high probability of 0.714 for a recurvature of greater than 90°. The most taken direction of movement of typhoons around the Western North Pacific were analysed in different ways and along the 16 points of compass, the direction from 270° to 292.5° was found to be the most preferred direction of movement.

New predictors and a new prediction model for the typhoon frequency over western North Pacific

In this paper, the impacts of the atmospheric circulation during boreal winter-spring on the western North Pacific (WNP) typhoon frequency (WNPTF) are studied. Several new factors in winter-spring in- fluencing the typhoon frequency were identified, including the sea ice cover in the North Pacific and the North Pacific oscillation. Based on these results, the multi-linear regression was applied to establishing a new forecast model for the typhoon frequency by using the datasets of 1965―1999. The forecast model shows a high correlation coefficient (0.79) between the model simulated and the actual typhoon frequencies in the period of 1965―1999. The forecast model also exhibits reasonable hindcasts for the typhoon frequencies for the years 2000―2006. Therefore, this work demonstrates that the new pre- dictors are significant for the prediction of the interannual variability of the WNPTF, which could be potentially used in the operational seasonal forecast of the typhoon frequency in the WNP to get a more physically based operational prediction model and higher forecast skill.

Tropical cyclones and multiscale climate variability: The active western North Pacific typhoon season of 2018

The 2018 typhoon season in the western North Pacific(WNP) was highly active, with 26 named tropical cyclones(TCs) from June to November, which exceeded the climatological mean(22) and was the second busiest season over the past twenty years. More TCs formed in the eastern region of the WNP and the northern region of the South China Sea(SCS). More TCs took the northeast quadrant in the WNP, recurving from northwestward to northward and causing heavy damages in China's Mainland(69.73 billion yuan) in 2018. Multiscale climate variability is conducive to an active season via an enhanced monsoon trough and a weakened subtropical high in the WNP. The large-scale backgrounds in 2018 showed a favorable environment for TCs established by a developing central Pacific(CP) El Ni?o and positive Pacific meridional mode(PMM)episode on interannual timescales. The tropical central Pacific(TCP) SST forcing exhibits primary control on TCs in the WNP and large-scale circulations, which are insensitive to the PMM. During CP El Ni?o years, anomalous convection associated with the TCP warming leads to significantly increased anomalous cyclonic circulation in the WNP because of a Gill-type Rossby wave response. As a result, the weakened subtropical high and enhanced monsoon trough shift eastward and northward, which favor TC genesis and development. Although such increased TC activity in 2018 might be slightly suppressed by interdecadal climate variability, it was mostly attributed to the favorable interannual background. In addition, high-frequency climate signals,such as intraseasonal oscillations(ISOs) and synoptic-scale disturbances(SSDs), interacted with the enhanced monsoon trough and strongly modulated regional TC genesis and development in 2018.

Can the climate background of western North Pacific typhoon activity be predicted by climate model?

Based on the observation and reanalysis data through 1948―2004, the vertical shear of zonal wind, outgoing longwave radiation, and divergence fields in the lower and upper troposphere during summer are revealed to correlate significantly with the concurrent western North Pacific (WNP) typhoon fre-quency, and they therefore can be regarded as predictors for the WNP typhoon activity anomaly. After that, the 34-year (1970―2003) ensemble hindcast experiments are performed by the nine-level atmos-pheric general circulation model developed at the Institute of Atmospheric Physics Under the Chinese Academy of Sciences (IAP9L-AGCM), aiming to investigate the numerical predictability of the summer vertical shear of zonal wind and divergence field in the lower troposphere. It is found that the temporal correlation coefficients between the hindcast and observation are 0.70 and 0.62 for the vertical shear of zonal wind and divergence field, respectively. This suggests that the model possesses a large potential skill for predicting the large-scale climate background closely related to the WNP typhoon activity, and the model is therefore capable of performing the real-time numerical prediction of the WNP typhoon activity anomaly to some extent.

Interaction Between Typhoon and Western Pacific Subtropical Anticyclone:Data Analyses and Numerical Experiments

Three kinds of typhoons with distinct tracks are sorted based on a set of typhoon data from 1958 to 1998. The results of composite analyses confirm that different typhoon tracks correspond to different patterns of the subtropical anticyclone over the western Pacific （SAWP）. When the tracks are westward, the SAWP is strong, with a zonal form, and stretches westward; when the tracks are recurving, the main body of the SAWP shifts eastward and breaks near 160~E; and when the tracks are northward, the SAWP is located far east of its normal position. Based on the above result, two different initial fields are configured, one has a zonal and strong SAWP, and the other has a meridional and weak SAWP. By using the GOALS R42L9 climate model, a temperature disturbance is added into these two different initial fields to force the formation of a typhoon. Westward and northward tracked typhoons are well simulated, thus verifying that different patterns of the SAWP have different effects on typhoon tracks. Results also show that typhoons can induce barotropic Rossby waves propagating to the mid and high latitudes. Under different background zonal flows, the wave trains triggered by the typhoons of westward and northward tracks are also different, and their effects on the mid and high latitude circulations and the SAWP are different. Compared to a n.orthward tracked typhoon, a westward tracked typhoon is able to induce positive geopotential height anomaly to its north and northwest, resulting in the SAWP strengthening and developing westward.

Interdecadal variation of tropical cyclone activity in association with summer monsoon,sea surface temperature over the western North Pacific

Based on geographic division over the western North Pacific(WNP),the interdecadal relationships between summer monsoon,sea surface temperature(SST) and tropical cyclones activity(including number,track and intensity) are examined.In the past several decades,the western Pacific subtropical high(WPSH) and tropical westerlies contribute to the interdecadal variation of TC number in the northwest and southeast of WNP respectively.The increased TC occurrence density to the east of Philippines related to TC track appears during the 1990s,in terms of both steer flow induced by WPSH and genesis location.From the interdecadal viewpoint,the tendency of TC intensity,measured by averaged accumulated cyclone energy,does well agree with that of SST,implying that SST plays an important role in TC intensity.

基于静止气象卫星监测西太平洋火山活动

利用自主开发的静止气象卫星实时热点监测系统所积累的西太平洋2020~2023年卫星热点监测数据,结合全球火山活动计划(GVP)发布的全新世火山列表数据,在分析火山活动热辐射特征的基础上,提出一种基于静止气象卫星热点观测数据的火山活动监测算法,通过聚类识别技术从卫星热点数据中提取火山热点并计算火山热辐射指数。对比分析火山监测结果与GVP火山活动报告可知,该算法的火山活动识别率约为90%。漏报火山主要位于印度尼西亚地区,受火山活动类型和热带对流云系的影响。根据火山热点地理分布及其时间变化可以估算熔岩流蔓延方向、距离和速度。卫星火山热点监测数据在实时运行模式下可以作为输入因子之一驱动火山活动预报模型实时发布火山预警信息,其历史数据还可以作为高时间分辨率数据源支持火山活动研究。

Relationships between the North Pacific Oscillation and the typhoon/hurricane frequencies

Relationships between the North Pacific Oscillation (NPO) and the typhoon as well as hurricane fre-quencies are documented. The correlation between NPO index in June-July-August-September and the annual typhoon number in the western North Pacific is 0.37 for the period of 1949―1998. The NPO is correlated with the annual hurricane number in the tropical Atlantic at -0.28 for the same period. The variability of NPO is found to be concurrent with the changes of the magnitude of vertical zonal wind shear, sea-level pressure patterns, as well as the sea surface temperature, which are physically asso- ciated with the typhoons and hurricanes genesis. The NPO associated atmospheric circulation vari- ability is analyzed to explain how NPO is linked with variability of the tropical atmospheric circulation in the western Pacific and the tropical Atlantic, via the atmospheric teleconnection.

西太平洋台风活动对中国西北地区东部夏季降水的影响

基于1979~2020年(42年)降水及台风资料,利用常用的统计方法和随机森林方法,研究了西太平洋台风对我国西北地区东部(33°N~45°N,93°E~110°E,ENWC)降水的影响。结果发现,在台风频数和降水量都出现峰值的7、8、9月,出现在西北太平洋的台风对台风期间的ENWC平均日降水(TP)有影响。7月份台风的位置和强度对降水影响显著,8月份台风的位置、强度和频数对降水都有影响,9月份影响较小。台风的影响具有地域选择性,不同的月份这种选择性不同,对不同等级降水的影响也不同。其影响主要表现在EOF分解的第二模态以及强降水和极强降水等级上,这说明了台风不是影响TP的主要因素,这种影响是间接的和非线性的,台风的出现是通过影响东亚地区中高纬度的槽脊系统、西太平洋副热带高压以及低纬度低涡的强度和位置来形成有利于降水的条件,从而影响降水的分布和强度。相对于多元线性回归方法,基于随机森林方法建立的降水模型能更好地拟合出降水分布和强度,这说明台风对TP的影响主要是非线性的,且降水强度越强,非线性作用越明显。同时,随机森林模型也显示出台风的位置是影响ENWC降水的最关键因素。

“23·7”华北极端暴雨精细特征和天气学成因分析

2023年7月29日至8月1日,华北京津冀地区遭受极端特大暴雨袭击,导致区域性洪涝灾害,造成重大经济损失和人员伤亡。为探明此次“23·7”华北极端降水过程的基本特征和形成原因,基于地面自动气象站分钟级降水资料、风廓线雷达和雨滴谱仪观测资料及ERA5再分析数据,揭示了“23·7”华北极端暴雨的精细特征和天气学成因。结果表明:(1)此次降水过程持续时间长、累计雨量极大,特大暴雨落区、突破降水量历史极值的国家级观测站站点密集分布在京津冀太行山近山地区,降水呈现显著极端性、区域性差异和阶段性变化。河北和北京太行山东侧迎风坡地区出现持续性、强度相对稳定的强降水过程,雨滴谱分布偏向于高雨滴数密度、小雨滴直径的海洋型对流降水;京津冀平原地区过程雨量明显小于山区,但中尺度对流雨带活跃,降水阵性、对流性特征明显。(2)在“杜苏芮”台风残涡、西太平洋副热带高压、大陆高压等天气系统协同作用下,中层位势高度场出现罕见的“北高南低”+“西低东高”的稳定天气形势。北上台风“杜苏芮”残涡在高压坝以及太行山、燕山地形影响下移动缓慢,残涡中心北侧的地形障碍流与低空东南风之间形成稳定倒槽,京津冀地区出现持续性低层辐合,同时配合来自南海季风和东部洋面台风“卡努”的双路水汽输送,导致京津冀地区出现长历时、区域性极端暴雨过程。(3)在阶段性降水发展过程中,与台风残涡相关的倒槽、暖切变线、低空急流等精细结构调控了中尺度对流系统的组织和发展特征,7月31日早晨至上午京津冀地区出现超过22 m/s的超低空东南风急流,配合对流和地形抬升等因素影响,降水强度明显增强,北京西部山前出现超100 mm/h的极端雨强。此次极端降水事件中的地形影响、中小尺度特征以及极端暴雨可预报性等问题尚待更深入研究。