Pathways of Influence of the Northern Hemisphere Mid–high Latitudes on East Asian Climate: A Review

This paper reviews recent progress made by Chinese scientists on the pathways of influence of the Northern Hemisphere mid-high latitudes on East Asian climate within the framework of a“coupled oceanic-atmospheric(land-atmospheric or seaice-atmospheric)bridge”and“chain coupled bridge”.Four major categories of pathways are concentrated upon,as follows:Pathway A—from North Atlantic to East Asia;Pathway B—from the North Pacific to East Asia;Pathway C—from the Arctic to East Asia;and Pathway D—the synergistic effects of the mid-high latitudes and tropics.In addition,definitions of the terms“combined effect”,“synergistic effect”and“antagonistic effect”of two or more factors of influence or processes and their criteria are introduced,so as to objectively investigate those effects in future research.

Contrast between the Climatic States of the Warm Pool in the Indian Ocean and in the Pacific Ocean

Based on the analysis of Levitus data, the climatic states of the warm pool in the Indian Ocean (WPIO) and in the Pacific Ocean (WPPO) are studied. It is found that WPIO has a relatively smaller area, a shallower bottom and a slightly lower seawater temperature than those of WPPO. The horizontal area at different depths, volumes, central positions, and bottom depths of both WPIO and WPPO show quite apparent signals of seasonal variation. The maximum amplitude of WPIO surface area’s seasonal variation is 58% larger over the annual mean value. WPIO’s maximum volume variation amplitude is 66% larger over the annual mean value. The maximum variation amplitudes of the surface area and volume of WPPO are 20. 9% and 20.6% larger over the annual mean value respectively. WPIO and WPPO show different temporal and spatial characteristics mainly due to the different wind fields and restriction of ocean basin geometry. For instance, seasonal northern displacement of WPIO is, to some extent, constrained by the basin of the Indian Ocean, while WPPO moves relatively freely in the longitudinal direction. The influence of WPIO and WPPO over the atmospheric motion must be quite different.

Interannual Variability and Scenarios Projection of Sea Ice in Bohai Sea Part Ⅰ: Variation Characteristics and Interannual Hindcast

The Bohai Sea is one of the southernmost areas for sea ice formation in the northern hemisphere.Sea ice disasters in this body of water severely affect marine activities and the safety of coastal residents.In this study,we analyze the variation characteristics of the sea ice in the Bohai Sea and establish an annual regression model based on predictable mode analysis method.The results show the following:1)From 1970 to 2018,the average ice grade is(2.6±0.8),with a maximum of 4.5 and a minimum of 1.0.Liaodong Bay(LDB)has the heaviest ice conditions in the Bohai Sea,followed by Bohai Bay(BHB)and Laizhou Bay(LZB).Interannual variation is obvious in all three bays,but the linear decreasing trend is significant only in BHB.2)Three modes are obtained from empirical orthogonal function analysis,namely,single polarity mode with the same sign of anomaly in all of the three bays and strong interannual variability(82.0%),the north–south dipole mode with BHB and LZB showing an opposite sign of anomalies to that in LDB and strong decadal variations(14.5%),and a linear trend mode(3.5%).Critical factors are analyzed and regression equations are established for all the principal components,and then an annual hindcast model is established by synthesizing the results of the three modes.This model provides an annual spatial prediction of the sea ice in the Bohai Sea for the first time,and meets the demand of operational sea ice forecasting.

Quantitative Comparison of Predictabilities of Warm and Cold Events Using the Backward Nonlinear Local Lyapunov Exponent Method

The backward nonlinear local Lyapunov exponent method(BNLLE)is applied to quantify the predictability of warm and cold events in the Lorenz model.Results show that the maximum prediction lead times of warm and cold events present obvious layered structures in phase space.The maximum prediction lead times of each warm(cold)event on individual circles concentric with the distribution of warm(cold)regime events are roughly the same,whereas the maximum prediction lead time of events on other circles are different.Statistical results show that warm events are more predictable than cold events.

Intermodel Diversity of Simulated Long-term Changes in the Austral Winter Southern Annular Mode:Role of the Southern Ocean Dipole

The Southern Annular Mode(SAM)plays an important role in regulating Southern Hemisphere extratropical circulation.State-of-the-art models exhibit intermodel spread in simulating long-term changes in the SAM.Results from Atmospheric Model Intercomparison Project(AMIP)experiments from 28 models archived in CMIP5 show that the intermodel spread in the linear trend in the austral winter(June−July−August)SAM is significant,with an intermodel standard deviation of 0.28(10 yr)−1,larger than the multimodel ensemble mean of 0.18(10 yr)−1.This study explores potential factors underlying the model difference from the aspect of extratropical sea surface temperature(SST).Extratropical SST anomalies related to the SAM exhibit a dipole-like structure between middle and high latitudes,referred to as the Southern Ocean Dipole(SOD).The role of SOD-like SST anomalies in influencing the SAM is found in the AMIP simulations.Model performance in simulating the SAM trend is linked with model skill in reflecting the SOD−SAM relationship.Models with stronger linkage between the SOD and the SAM tend to simulate a stronger SAM trend.The explained variance is about 40%in the AMIP runs.These results suggest improved simulation of the SOD−SAM relationship may help reproduce long-term changes in the SAM.

Controls on the Northward Movement of the ITCZ over the South China Sea in Autumn:A Heavy Rain Case Study

The autumn Intertropical Convergence Zone(ITCZ)over the South China Sea(SCS)is typically held south of 10°N by prevailing northeasterly and weakening southwesterly winds.However,the ITCZ can move north,resulting in heavy rainfall in the northern SCS(NSCS).We investigate the mechanisms that drove the northward movement of the ITCZ and led to heavy non-tropical-cyclone rainfall over the NSCS in autumn of 2010.The results show that the rapid northward movement of the ITCZ on 1 and 2 October was caused by the joint influence of the equatorial easterlies(EE),southwesterly winds,and the easterly jet(EJ)in the NSCS.A high pressure center on the east side of Australia,strengthened by the quasi-biweekly oscillation and strong Walker circulation,was responsible for the EE to intensify and reach the SCS.The EE finally turned southeast and together with enhanced southwesterly winds associated with an anticyclone,pushed the ITCZ north.Meanwhile,the continental high moved east,which reduced the area of the EJ in the NSCS and made room for the ITCZ.Further regression analysis showed that the reduced area of the EJ and increased strength of the EE contributed significantly to the northward movement of the ITCZ.The enhancement of the EE preceded the northward movement of the ITCZ by six hours and pushed the ITCZ continually north.As the ITCZ approached 12°N,it not only transported warm moist air but also strengthened the dynamic field by transporting the positive vorticity horizontally and vertically which further contributed to the heavy rainfall.

Application of Backward Nonlinear Local Lyapunov Exponent Method to Assessing the Relative Impacts of Initial Condition and Model Errors on Local Backward Predictability

Initial condition and model errors both contribute to the loss of atmospheric predictability.However,it remains debatable which type of error has the larger impact on the prediction lead time of specific states.In this study,we perform a theoretical study to investigate the relative effects of initial condition and model errors on local prediction lead time of given states in the Lorenz model.Using the backward nonlinear local Lyapunov exponent method,the prediction lead time,also called local backward predictability limit(LBPL),of given states induced by the two types of errors can be quantitatively estimated.Results show that the structure of the Lorenz attractor leads to a layered distribution of LBPLs of states.On an individual circular orbit,the LBPLs are roughly the same,whereas they are different on different orbits.The spatial distributions of LBPLs show that the relative effects of initial condition and model errors on local backward predictability depend on the locations of given states on the dynamical trajectory and the error magnitudes.When the error magnitude is fixed,the differences between the LBPLs vary with the locations of given states.The larger differences are mainly located on the inner trajectories of regimes.When the error magnitudes are different,the dissimilarities in LBPLs are diverse for the same given state.

Evaluation of the performance of CMIP5 and CMIP6 models in simulating the South Pacific Quadrupole-ENSO relationship

先前的观测研究表明,南太平洋四极子海温模态(SPQ)可以有效地作为ENSO的前兆信号.本文利用20个CMIP6模式及其对应的20个先前的CMIP5模式的工业化前气候模拟试验数据,评估和比较了CMIP6以及CMIP5模式对SPQ与ENSO的关系的模拟能力.结果表明,大多数CMIP5和CMIP6模式可以合理地模拟SPQ的基本特征.与早期的CMIP5模式相比,CMIP6模式能够更加真实地模拟SPQ与ENSO之间的关系.进一步分析表明,CMIP6模式模拟SPQ与ENSO关系的能力提高,是因为CMIP6模式能够更好地模拟出在副热带/热带太平洋上与SPQ相关的表面海气热力耦合过程,以及在赤道太平洋上与SPQ相关的次表层海温的异常相应.

Circulations and Thermodynamic Characteristics of Different Patterns of Rainstorm Processes in the Eastern Foot of Helan Mountain

Based on the observational hourly precipitation data and the European Centre for Medium-Range Weather Forecasts(ECMWF)Reanalysis 5(ERA5)products from 2006 to 2020,22 rainstorm processes in the eastern foot of Helan Mountain are objectively classified by using the hierarchical clustering method,and the circulation characteristics of different patterns are comparatively analyzed in this study.The results show that the occurrences of rainstorm processes in the eastern foot of Helan Mountain are most closely related to three circulation patterns.PatternsⅠandⅢmainly occur in July and August,with similar zonal circulations in synoptic backgrounds.Specifically,the South Asia high and the western Pacific subtropical high are stronger and more northward than those in normal years.The frontal systems in westerlies are inactive,while the water vapor from the ocean surface in the south is mainly transported to the rainstorm area by the southerly jet stream at 700 h Pa.The dynamic lifting anomalies are relatively weak,the instability of atmospheric stratification is anomalously strong,and thus the localized severe convective rainstorm is more significant.Comparatively,rainstorm processes of patternⅠare accompanied by stronger and deeper ascending motions,and the warm-sector rainstorm is more extreme.PatternⅢshows a stronger and deeper convective instability,accompanied by larger low-level moisture.Rainstorm processes of patternⅡmainly occur in early summer and early autumn,presenting a meridional circulation pattern of high in the east and low in the west in terms of geopotential height.Moreover,the two low-level jets transporting the water vapor northward from the ocean on the east of China encounter with the frontal systems in westerlies,which makes the ascending motion in patternⅡanomalously strong and deep.The relatively weak instability of atmospheric stratification causes weak convection and long-lasting precipitation formed by the confluence of cold air and warm air.This study may help improve rainstorm forecasting in arid regions.

全球变暖导致易诱发臭氧污染的强地面太阳辐射频率增加

世界卫生组织2021年提出了新的臭氧标准,不仅加严了原有的短期暴露标准,还增加了暖季峰值的长期暴露指标.2019年秋季我国发生了大范围臭氧污染事件,特别是珠三角地区臭氧浓度异常增加最为突出,导致其暖季峰值超标,并且2019年长时间臭氧污染事件增幅更大.本文发现地面太阳辐射与臭氧年际变化相关性远高于其他气象因子,即使在温度较低时,较强的太阳辐射依然可促进高臭氧浓度累积.数值模式显示强太阳辐射驱动天然源大幅增加,不仅促进臭氧浓度升高,更重要的是,对于长时间臭氧污染事件频率增加大于短期污染事件,从而大大促进臭氧超标天数的增加.结合高分辨率地球系统模式和多模式比较计划,一致揭示在全球变暖下中国东部、美国东南部、欧洲各国,未来地面太阳辐射显著增加.通过将秋季地面太阳辐射日异常标准化,构建了臭氧气象指数,可有效揭示高臭氧浓度,阐明在北半球多个易发生臭氧污染区域,高臭氧气象指数天气发生频率显著增加,即利于高臭氧污染发生的气象条件在全球变暖下可能会更加频繁地发生.

A NONHYDROSTATIC NUMERICAL MODEL FOR DENSITY STRATIFIED FLOW AND ITS APPLICATIONS

A modular numerical model was developed for simulating density-stratified flow in domains with irregular bottom topography. The model was designed for examining interactions between stratified flow and topography, e.g,, tidally driven flow over two-dimensional sills or internal solitary waves propagating over a shoaling bed. The model was based on the non-hydrostatic vorticity-stream function equations for a continuously stratified fluid in a rotating frame. A self-adaptive grid was adopted in the vertical coordinate, the Alternative Direction Implicit （ADI） scheme was used for the time marching equations while the Poisson equation for stream-function was solved based on the Successive Over Relaxation （SOR） iteration with the Chebyshev acceleration. The numerical techniques were described and three applications of the model were presented.

THREE-DIMENSIONAL NUMERICAL SIMULATION OF THE MESOSCALE WIND STRUCTURE OVER SHANDONG PENINSULA

General features of 3-dimensional mesoscale wind and temperature structure over Shandong Peninsula are described in this paper.Results are achieved by numerical simulation with the 3- dimensional non-hydrostatic mesoscale model METRAS.For the onset and cessation time of sea- land breezes,the simulation results agree well with the statistical analyses of observational data available for the studied area.One interesting result is the 3 hour response time of wind field to the thermal change.Further statistic analysis based on the observational data is needed to make sure of this correlation.Important effects of coastal mountains on the wind structure are also exposed in detail by the model.Convergence and divergence centers resulting from the conjunction of sea-land breezes and complex terrain are clearly shown,which are not noticed before by conventional synoptic observation and theoretical analysis.

The barrier layer in the south-ern region of the South China Sea

By analysing the CTD data in the southernregion of the South China Sea gathered during six cruisesbetween 1989 and 1999, a barrier layer with seasonalvariation just like what exists in the equatorial oceans isfound in this region. It is the first discovery in such amarginal sea yet. It is strong in autumn and a little weak in summer and winter. The thicker the barrier layer, the higher the average temperature of the upper mixed layer. The region with the thicker barrier layer overlaps the region with thehigher average temperature of the upper mixed layer, andaccords with the thicker region of the warm pool in the South China Sea got from the Levitus data. The barrier layer in the southern region of the South China Sea has significantinfluence on the heat storage of the upper ocean there.

Relations between mercury fractions and microbial community components in seawater under the presence and absence of probable phosphorus limitation conditions

Microbial transformations of toxic monomethylmercury(MMHg) and dissolved gaseous mercury(DGM) at the lower levels of the marine food web are not well understood, especially in oligotrophic and phosphorus-limited seas. To examine the effects of probable phosphorus limitation(~PP-limitation) on relations between mercury(Hg) fractions and microorganisms, we determined the total mercury(THg), total methylated mercury(MeHg), DGM, and microbiological and chemical parameters in the Central Adriatic Sea. Using statistical analysis, we assessed the potential microbial effects on Hg transformations and bioaccumulation. Only in the absence of ~PP-limitation conditions(^(NO–P)P-limitation) is MeHg significantly related to most chemical and microbial parameters, indicating metabolism-dependent Hg transformations.The heterotrophic activity of low nucleic acid bacteria(abundant in oligotrophic regions)seems responsible for most of Hg methylation under ^(NO–P)P-limitation. Under these conditions,DGM is strongly related to microbial fractions and chlorophyll a, indicating biological DGM production, which is probably not metabolically induced, as most of these relations are also observed underPP-limitation. MMHg biomagnification was observed through an increased bioaccumulation factor from microseston to mesozooplankton. Our results indicate that Hgtransformations and uptake might be enhanced under ^(NO–P)P-limitation conditions, emphasizing their impact on the transfer of Hg to higher trophic levels.