The Role of Topography and Diabatic Heating in the Formation of Dipole Blocking in the Atmosphere

In this paper, the nonlinear stationary waves forced by topography and diabatic heating are investigated. It is pointed out that (1) the nonlinear interaction of different stationary waves forced only by topography might form dipole blocking in the atmosphere, this might explain the dipole blocking appeared in the Pacific and Atlantic regions; (2) the dipole blocking could not be caused by the nonlinear interaction of the different stationary waves forced by the diabatic heating alone; (3) the nonlinear interaction of the diffferent stationary waves forced by both topography and diabatic heating could initiate dipole blocking in the atmosphere. In winter, the dipole blocking mainly occurs in the west regions of the Pacific and the Atlantic, and the heat source over the western part of the two oceans is advantageous to the formation of dipole blocking in the west of two oceans. However, in summer, the dipole blocking could be formed in the east part of the two oceans, and the heat source over the eastern     

Role of Ozone in the Sodium and Hydroxyl Nightglow

One-dimensional photochemical diffusion model which includes oxygen-hydrogen-sodium atmosphere has been used to examine the relation between sodium and hydroxyl nightglow and the role of ozone in it. It is found that both emissions can be obtained on the basis of photochemistry. The following reactionsNa + O3→jNaO + O2and H + O3→OH*+O2play key role in sodium and hydroxyl emission respectively. Further it is found that variations in both emissions are controlled by the variation in the concentration of ozone.     

Relationship between the Interannual Variations of Total Ozone in the Northern Hemisphere and the QBO of Basic Flow in the Tropical Stratosphere

The harmonic analyses of monthly mean total ozone in the atmosphere over the Northern Hemisphere for 26 years (1960-1985) are made by using the Fourier expansion. The analysed results show that there is obviously a quasi-biennial oscillation (QBO) in the interannual variations of the amplitudes of total ozone. Generally, the amplitudes of wavenumber 1 and 2 during the westerly of the equatorial QBO are larger than those during the easterly. In the early winter, the amplitude of wavenumber 1 during the easterly phase is larger, and in the late winter, it is larger during the westerly phase. These are in good agreement with the observational distributions.     

Longitudinal Displacement of the Subtropical High in the Western Pacific in Summer and its Influence

Using the relative vorticity averaged over a certain area, a new index for measuring the longitudinal position of the subtropical high (SH) in the western Pacific is proposed to avoid the increasing trend of heights in the previous indices based on geopotential height. The years of extreme westward and eastward extension of SH using the new index are in good agreement with those defined by height index. There exists a distinct difference in large-scale circulation between the eastward and westward extension of SH under the new definition, which includes not only the circulation in the middle latitudes but also the flow in the lower latitudes. It seems that when the SH extends far to the east (west), the summer monsoon in the South China Sea is stronger (weaker) and established earlier (later). In addition, there exists a good relationship between the longitudinal position of SH and the summer rainfall in China. A remarkable negative correlation area appears in the Changjiang River valley, indicating that when the SH extends westward (eastward), the precipitation in that region increases (decreases). A positive correlation region is found in South China, showing the decrease of rainfall when the SH extends westward. On the other hand, the rainfall is heavier when the SH retreats eastward. However, the anomalous longitudinal position of SH is not significantly related to the precipitation in North China. The calculation of correlation coefficients between the index of longitudinal position of SH and surface temperature in China shows that a large area of positive values, higher than 0.6 in the center, covers the whole of North China, even extending eastward to the Korean Peninsula and Japan Islands when using NCEP/NCAR reanalysis data to do the correlation calculation. This means that when the longitudinal position of the SH withdraws eastward in summer, the temperature over North China is higher. On the other hand, when it moves westward, the temperature there is lower. This could explain the phenomenon of the seriously high temperatures over North China during recent summers, because the longitudinal position of SH in recent summers was located far away from the Asian continent. Another region with large negative correlation coefficients is found in South China.     

Effect of Counter-Gradient in the Computation of Turbulent Fluxes of Heat and Moisture in a Regional Model

The counter-gradient terms in the computations of turbulent fluxes of heat and moisture have been included in the PBL parameterization of a regional model for monsoon prediction. Results show that inclusion of counter-gradient terms has a marginal impact in the prediction of large scale monsoon circulation and rainfall rates.     

Synchronous Characteristics of Precipitation Extremes in the Yangtze and Murray–Darling River Basins and the Role of ENSO

The floods caused by the extreme precipitation in the Yangtze River basin(YRB) and Murray–Darling River basin(MDRB), the largest basins in China and Australia, have significant impacts on the society and regional economies.Based on the spatial–temporal analysis of the daily precipitation extremes(DPEs) during 1982–2016, we found that for both basins, the whole-basin-type DPEs have the highest proportion and a synchronous DPE interannual variation characteristic exists in the two basins, with the 3-yr running correlation coefficient of the annual DPE days(DPEDs) reaching almost 0.7(significant at the 0.01 level). The El Ni?o–Southern Oscillation(ENSO), which is one of the most significant climate disturbance factors in the world, plays an important role in modulating the variability of the DPEs in the two basins. Singular value decomposition(SVD) analysis revealed that both the YRB and the MDRB's whole-basin-type DPEs are closely coupled with the procedure that the preceding winter eastern Pacific(EP)-type El Ni?o faded to a central Pacific(CP)-type La Ni?a. This means that the DPEs in the YRB and MDRB may synchronously occur more frequently when the above process occurs. Owing to the atmosphere–ocean interaction from the east–west dipole sea surface temperature(SST) anomaly pattern, the atmospheric circulation disturbance exhibits a pattern in which the equatorial eastern Pacific region is a mass source anomaly with a higher pressure,drier air, and weaker convection, while the equatorial western Pacific region is a mass sink anomaly with a lower pressure, wetter air, and stronger convection. Moreover, two wave trains that originated from the tropical western Pacific were found to extend to the YRB and MDRB. The interaction between the wave train's interphase dynamics and water vapor transport disturbance results in the ascent conditions and enhanced water vapor transport, which leads to the synchronous occurrence of DPEs in the YRB and MDRB on an interannual scale.     

Divide and conquer—Discursive agency in the politics of illegal logging in the United States

In 2008 the US amended the century-old US Lacey Act to prohibit the import of illegally harvested or traded timber. Together with similar policies in the EU and Australia, this initialized a paradigm shift in global forest governance towards a legality (verification) regime that could substantially contribute to environmental and social stewardship in the forest sector. The analysis of the formation and implementation of these new policies in the US, Europe and Australia is, however, only just beginning.Based on 31 semi-structured interviews with key stakeholders, 19 informal conversations, more than 100 documents, and participant observation data, we analyze the policy making and implementation of the 2008 US Lacey Act amendment. Our results suggest two essential drivers for this policy change: (1) the deployment of discursive divide-and-conquer strategies and (2) a shift away from sustainability to legality, on both the international level and in the US. Based on the Discursive Agency Approach, we illustrate how carefully deployed discursive and governance strategies were crucial for building a coalition between environmentalists and parts of the wood (products) industry. This coalition was able to create a powerful storyline that muted the opposition and presented a politically attractive amendment proposal. We further show how these strategies have significant effects on the perception of the amended Lacey Act and its implementation. During implementation, coalitions as well as discursive and governance strategies shifted substantially but were still determined by the pre-amendment policy discourse. We conclude by exploring the importance of our findings for what we might expect from the concept of legality in global forest and environmental governance.     

Interannual and Interdecadal Variations in Heat Content of the Upper Ocean of the South China Sea

The vertically averaged temperature (TAV) from surface to 100 m depth of the South China Sea for the period 1959-1988 is analyzed. The results indicate that there is a significant long-term variability from interannual to interdecadal scales in the heat content in the upper ocean. The heat content of the upper ocean of the South China Sea increases evidently in the El Nino year. TAV anomaly in the ocean was negative from the end of 1950’s to early l970’s, and then changed to positive. The changes of TAV of the ocean are closely related to ENSO events, the Asian winter monsoon and the tropical atmospheric circulation anomalies.     

An OGCM Simulation of Seasonal and Interannual Variabilities in the Surface-Layer Pacific of the Equatorial Band

l. IntroductionThe physical mechanisms contro1ling t]de El Nifio event have been studied based on ob-servations in the equatorial Pacific (Weare l983; Reed l986; Hayes et al. l99l; McPhadenand Picaut l990; Frankignoul et al. 1996; Weisberg and Wang l997). One of the most impor-tant issues is whether the surface heat flux ojr ocean advective heat fluxes are dominant in con-trolling the sea surface temperature (SST). Some studies indicated that the SST is mainly con-trolled by the surface…     

Areal distribution and precipitation–altitude relationship of heavy short-term precipitation in the Czech Republic in the warm part of the year

The article presents an analysis of heavy short-term precipitation for the warm part of the year in the Czech Republic (CR). Precipitation data are prepared for the years 2002–2007 with a horizontal resolution of 1 km and a temporal resolution of 1 h. A method merging radar and daily rain gauge measurements is applied to calculate basic hourly precipitation. Two types of 1-, 2-, 3-, and 6-h precipitation data, derived from the basic hourly precipitation, are investigated from the viewpoint of precipitation–altitude relationships and areal distributions of heavy precipitation. The first type of data consists of sums of hourly precipitation, where the summation is performed for all data regardless of whether the summed hourly precipitation is a part of a longer precipitation event or if some hours are without precipitation. The second type of data contains temporally bounded precipitation events. This type predominantly includes convective precipitation. The results show that for both types of data, 1-h precipitation with high rain rates is without apparent dependence on altitude. For the first type of data and for precipitation durations of 2 and 3 h, the impact of altitude on precipitation maps can be identified for low and high rain rates. The impact of mountains is evident for the 6-h precipitation because it includes large scale precipitation events. However, the second type of data does not depend on altitude for heavy precipitation. Heavy precipitation of the second type shows, especially for 6-h, an increased frequency of occurrence in the south to central CR.     

Attribution of SST variability in global oceans and the role of ENSO

Based on a novel design of coupled model simulations where sea surface temperature (SST) variability in the equatorial tropical Pacific was constrained to follow the observed El Niño—Southern Oscillation (ENSO) variability, while rest of the global oceans were free to evolve, the ENSO response in SSTs over the other ocean basins was analyzed. Conceptually the experimental setup was similar to discerning the contribution of ENSO variability to interannual variations in atmospheric anomalies. A unique feature of the analysis was that it was not constrained by a priori assumptions on the nature of the teleconnected response in SSTs. The analysis demonstrated that the time lag between ENSO SST and SSTs in other ocean basins was about 6 months. A signal-to-noise analysis indicated that between 25 and 50 % of monthly mean SST variance over certain ocean basins can be attributed to SST variability over the equatorial tropical Pacific. The experimental setup provides a basis for (a) attribution of SST variability in global oceans to ENSO variability, (b) a method for separating the ENSO influence in SST variations, and (c) understanding the contribution from other external factors responsible for variations in SSTs, for example, changes in atmospheric composition, volcanic aerosols, etc.     

Topographically Forced Rossby Wave Instability and the Development of Blocking in the Atmosphere

In this paper, the linear stability of disturbance superimposed on basic state Rossby wave forced by topography is investigated, and pointed out that when a certain criterion is satisfied by the basic flow and the height of topography for the subresonance, the small disturbance may be unstable. Furthermore, we also compare the evolution of the instability disturbance with the development of blocking in the Pacific, and we suggested that the topographically forced Rossby wave instability may provide a possible mechanism for the development of blocking in the Pacific.     

Study of the climatological behaviors of Euro-Atlantic and West Asia blockings in the period of 1959–2018

In this study, comparison of blocking climatological behaviors is presented for the two periods of 1959–1988 and 1989–2018 in a part of the Northern Hemisphere including the Atlantic Ocean, Europe and West Asia regions. Blocking events were detected using a modified blocking index that is based on vertically integrated potential vorticity. By applying this index, the characteristics of detected blocking events such as frequency, duration, intensity and area were determined and compared for both the periods.According to the results, on average, 16 and 15 blocking events per year were identified in the first and second periods, respectively. The trend analysis shows that the number of blocking events in the period 1959–1988 was significantly decreased, while it was slightly increased in the period 1989–2018. Blocking activity was most prevalent from the eastern Atlantic through Europe to West Asia, but this longitude band exhibits a relatively eastward shift in the second period. In addition, the seasonal distributions are similar to those found in previous studies with the higher occurrence of blocking events during winter and autumn seasons and the lowest frequency in summer, as well as long-lasting events and greater intensity and extension in winter than the summer time, especially in the second period. These seasonal variations of blocking frequency may be due to synoptic scale eddies and planetary waves which are more active and stronger in the colder seasons than the other seasons. On the other hand, a comparison between the two periods shows that the blocking events tend to be more frequent over West Asia especially during summer in recent years. Although discrepancies between the two periods are not significant, they could be partly due to the impacts of climate change in recent decades.     

The Extreme Mei-yu Season in 2020: Role of the Madden-Julian Oscillation and the Cooperative Influence of the Pacific and Indian Oceans※

The middle and lower reaches of the Yangtze River in eastern China during summer 2020 suffered the strongest mei-yu since 1961. In this work, we comprehensively analyzed the mechanism of the extreme mei-yu season in 2020, with focuses on the combined effects of the Madden-Julian Oscillation (MJO) and the cooperative influence of the Pacific and Indian Oceans in 2020 and from a historical perspective. The prediction and predictability of the extreme mei-yu are further investigated by assessing the performances of the climate model operational predictions and simulations. 　 It is noted that persistent MJO phases 1?2 during June?July 2020 played a crucial role for the extreme mei-yu by strengthening the western Pacific subtropical high. Both the development of La Ni?a conditions and sea surface temperature (SST) warming in the tropical Indian Ocean exerted important influences on the long-lived MJO phases 1?2 by slowing down the eastward propagation of the MJO and activating convection related to the MJO over the tropical Indian Ocean. The spatial distribution of the 2020 mei-yu can be qualitatively captured in model real-time forecasts with a one-month lead. This can be attributed to the contributions of both the tropical Indian Ocean warming and La Ni?a development. Nevertheless, the mei-yu rainfall amounts are seriously underestimated. Model simulations forced with observed SST suggest that internal processes of the atmosphere play a more important role than boundary forcing (e.g., SST) in the variability of mei-yu anomaly, implying a challenge in quantitatively predicting an extreme mei-yu season, like the one in 2020.     

Intraseasonal variability of sea level and circulation in the Gulf of Thailand: the role of the Madden–Julian Oscillation

Intraseasonal variability of the tropical Indo-Pacific ocean is strongly related to the Madden–Julian Oscillation (MJO). Shallow seas in this region, such as the Gulf of Thailand, act as amplifiers of the direct ocean response to surface wind forcing by efficient setup of sea level. Intraseasonal ocean variability in the Gulf of Thailand region is examined using statistical analysis of local tide gauge observations and surface winds. The tide gauges detect variability on intraseasonal time scales that is related to the MJO through its effect on local wind. The relationship between the MJO and the surface wind is strongly seasonal, being most vigorous during the monsoon, and direction-dependent. The observations are then supplemented with simulations of sea level and circulation from a fully nonlinear barotropic numerical ocean model (Princeton Ocean Model). The numerical model reproduces well the intraseasonal sea level variability in the Gulf of Thailand and its seasonal modulations. The model is then used to map the wind-driven response of sea level and circulation in the entire Gulf of Thailand. Finally, the predictability of the setup and setdown signal is discussed by relating it to the, potentially predictable, MJO index.     

Macro-and Micro-Structures of Heavy Fogs and Visibility in the Dayaoshan Expressway

Belonging to the southern subtropical moist type of monsoon climate,the Nanling mountainous area experiences heavy fogs whenever quasi-stationary fronts appear there from September to May.There can be as many as 15-18 days of heavy fogs per month.Fogs have more serious consequences in the Lechang-Ruyuan section of the Beijing-Zhuhai Expressway(the longest expressway in China)that passes through the main part of the Nanling Mts.,where the road rises from 200m to more than 800m above sea level(ASL).For a major motorway in the mountainous areas of Nanling Mts.,two multidisciplinary integrated field observations were carried out,which measured visibility by the naked eyes,visibility by instrument,spectrum of fog- drops,liquid water content(LWC)of fog,tethered sounding,dual-parameter low-level sounding,turbulence diffusion within fog layers,aerosol spectra of size and composition,sampled fog water compositions,and sampled rainwater compositions.Typical cases were probed for their analyses of synoptics,micro- and macro-structures and microphysics.It is understood that heavy fogs take place with high frequency in the area and bring about serious consequences.Being typical advection and upslope fogs,they are in essence low-lying clouds appearing at high altitudes,which are closely related with the activity of South China frontal processes,especially the South China quasi-stationary fronts,and reflect on the role of local terrain as well.The heavy fogs are characteristic of long duration,extremely low visibility,well-organized lump- shaped structure,large-size fog-drops,moderate concentration,high LWC,and stronger turbulent diffusion within the fog layers than in fine sky.They differ much from radiation fogs,which are better documented in previous study in China.It is found that fog LWC is in significant anti-correlation with visibility so that large LWC is associated with small visual range.It is also noted that one of the reasons for the fluctuation of characteristic quantities of micro-structure such as the LWC of fog in the area is,in addition to the inhomogeneous structure of the fog itself,the effect of advection and inhomogeneous underlying surface; during the translation of fog with the ambient wind,irregular upslope and cross-over movement is another reason for the inhomogeneous structure and fluctuation of fog.The spectrum of the aerosol size displays itself as the power function of monotonous descent.The concentration of submicrometer particles is even higher.The high-concentration sulfate particles found in the aerosols of Nanling Mts.are actually good nuclei for condensation,which are favorable for the formation of fog.The presence of fog can help cleanse the trace compositions in the atmosphere so that fog droplets contain high levels of polluting elements.In the meantime,compared to cloud droplets,fog droplets are easier to be captured by the vertical surfaces of objects on the land surface,such as vegetation and buildings to constitute another kird of cleansing process. In vast stretches of forest like the Nanling Mts.,this kind of cleansing may be quite important.Studying the characteristic variation of fogs in the area realistically assists in setting up a forecast and warning system for local fogs and provides basic information for fog dispersal experiments.     

Multivariate Objective Analysis of Wind and Height Fields in the Tropics

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The Characteristics and Controlling Factors of Water and Heat Exchanges over the Alpine Wetland in the East of the Qinghai–Tibet Plateau

Alpine wetland is one of the typical underlying surfaces on the Qinghai–Tibet Plateau. It plays a crucial role in runoff regulation. Investigations on the mechanisms of water and heat exchanges are necessary to understand the land surface processes over the alpine wetland. This study explores the characteristics of hydro-meteorological factors with in situ observations and uses the Community Land Model 5 to identify the main factors controlling water and heat exchanges.Latent heat flux and therm...     

The Phenomena of Bifurcation and Catastrophe of Large-Scale Horizontal Motion in the Atmosphere under the Effect of Rossby Parameter

The stability question of large-scale horizontal motion in the atmosphere under the effect of Rossby parameter is discussed in this paper by using the qualitative analysis theory of ordinary differential equations. The following aspects are reviewed: The stability of large-scale horizontal motion in the atmosphere accords with the common inertial stability criterion when the effect of Rossby parameter is not considered (Yang, 1983), and that, on the other hand, the motion will bifurcate two times with the variation of absolute vorticity of basic Zephyr flow at the initial position under the effect of Rossby parameter. Furthermore, in the inertial stable region, if the effect of geostrophic deviation at the initial position is considered, the motion will not only bifurcate but also generate a catastrophe.