In Part I of this study, the Ural blocking (UB)-induced amplification role of winter warm Arctic-cold Eurasian (WACE) anomalies has been examined. It was found that the long-lived UB together with the positive North Atlantic Oscillation (NAO 1 ) significantly contributes to the amplification of the WACE pattern. The present study examines how the UB variability affects quasi-biweekly WACE (QB-WACE) anomalies and depends on the NAO 1 and North Atlantic conditions by classifying the UB based on a case study of a cold event that occurred over southern China in January 2008. A composite analysis during 1979-2013 shows that the QB-WACE anomalies associated with the UB that often occur with the NAO 1 are strong and influenced by the North Atlantic jet (NAJ) and zonal wind strengths over Eurasia. For NAO 1 -related UB, the QB-WACE anomaly depends strongly on the location of UB, and the UB anomalies lag the NAO 1 by approximately 4-7 days.The strength of the NAJ determines whether the combined NAO 1 and UB anomalies exhibit a negative East Atlantic/West Russia (EA/WR 2 ) pattern, while the region of weak zonal winds over Eurasia and the zonal extent of the NAJ dominate the location of UB. For southward-, eastward-, and westward-displaced UBs associated with a strong NAJ, the NAO 1 favors the UB with a southward-displaced QB-WACE anomaly through wave train propagation like an EA/WR 2 pattern. Eastward-and southward-displaced UB anomalies induce similarly displaced cold anomalies with intrusion into southern China. However, for a northward-displaced UB, this happens without pronounced EA/WR 2 patterns because of a weak NAJ and is accompanied by a northward-displaced QB-WACE anomaly.

In this paper, the north-south variability of westerly jet anomalies during the two phases of the North Atlantic Oscillation (NAO) is examined in a theoretical model. It is found that the north-south variability of the zonal mean westerly anomaly results from the interaction between the eddy-driven anomalous stationary waves with a dipole meridional structure (NAO anomalies) and topographically induced climatological stationary waves with a monopole structure, which is dependent upon the phase of the NAO. The westerly jet anomaly tends to shift northward during the positive NAO phase but southward during the negative phase. Synoptic-scale eddies tend to maintain westerly jet anomalies through the excitation of NAO anomalies, but the climatological stationary wave and its position relative to the eddy-driven anomalous stationary wave appear to dominate the north-south shift of westerly jet anomalies.On the other hand, it is shown that when the climatological stationary wave ridge is located downstream of the eddy-driven anomalous stationary wave, the storm track modulated by the NAO pattern splits into two branches for the negative phase, in which the northern branch is generally stronger than the southern one. However, the southern one can be dominant as the relative position between anomalous and climatological stationary waves is within a moderate range. The storm track for the positive phase tends to drift northeastward when there is a phase difference between the NAO anomaly and climatological stationary wave ridge downstream. Thus, it appears that the relationship between the NAO jets and storm tracks can be clearly seen from the present theoretical model.

In this paper, a new two-dimensional blocking index is proposed by defining a difference between the daily 500-hPa geopotenial heights at the reference latitude and its north side. The reference latitude is determined by a composite latitude-dependent 500-hPa geopotenial height of blocking events in different seasons and sectors. The new index can take account of the duration, intensity, propagation, and spatial structure of a blocking event. Using this index, the characteristics (frequency, duration, intensity, and preferred occurrence region) of the blocking action in the North Hemisphere (NH) are investigated using a 42-yr sample of blocking events from the NCEP–NCAR reanalyses. It is found that blocking events in the NH are more frequent in the Atlantic–Europe sector than in the Pacific sector in winter and spring and autumn, but more persistent in the Atlantic–Europe sector than in the Pacific sector for all seasons. Blocking events in the Pacific sector tend to have larger amplitudes than the Atlantic counterparts. In addition, it is shown that in the NH independently occurring blocking events are most frequent, but simultaneously occurring blockings are rather rare, indicating that the blocking events in the NH should be a local phenomenon. On the other hand, a comparison with the existing indices [e.g., Tibaldi and Molteni (TM) index] indicates that in summer and autumn the new index shows similar longitudinal dependency of NH blocking events as does the TM index, but it shows two distinct action centers of blocking events in the Atlantic sector in winter and spring (in which the most frequent one is situated more westward) and an eastward blocking action center in the Pacific sector in spring and autumn, compared to the TM index. In addition, it is found that the new blocking index proposed here shows relatively low blocking frequency for all seasons compared to the TM index, especially in the Atlantic sector in spring and in the Pacific sector in winter and spring, which seems to be in agreement with the result obtained by Pelly and Hoskins using the PV–θ index.

Abstract. The conditions of 30 blocking events were examined at the time of onset over the 1993/1994-1996/1997 cold season (November to March). The antecedent synopticscale eddies in 83.3% of the total events are shown to induce a large-scale low/high eddy forcing pattern upstream of the incipient block, and the mean basic westerly flow is weak, 76.7% of which possesses cyclonic shear. It appears that both the antecedent synopticscale eddies that induce a low/high eddy forcing pattern and the weak background westerly flow (zonal wave number 0) that allows quasi-stationary preblock ridge are two necessary preconditions for the onset of blocking anticyclone, but the cyclonic shear of the background westerly flow is a favorable preblock environment. In addition, a theoretical model, represented by the superposition of dipole and monopole envelope Rossby solitons with weak orographic forcing for zonal wave number 2, is proposed to confirm these observations. It is found that the dipole envelope soliton is dominant and exhibits a quasi-2-week oscillation during the interaction between an antecedent blocking anticyclone and upstream synoptic-scale eddies. The monopole soliton tends to break up, indicating that blocking anticyclone circulation is dominated by the amplification of dipole component associated with synoptic-scale eddies. Finally, the evolution of time-dependent eddy feedback is shown to control the direction of planetary-scale potential vorticity transports induced by transient eddies, which is an indicator of the onset, maintenance, and decay of blocking. Moreover, the changes of amplified blocking anticyclone and synoptic-scale eddies obtained theoretically are also in agreement with those of observed blocking and synoptic eddies. IntroductionAtmospheric blocking has been studied extensively for several decades because of its important influence on weather and regional climate. However, predicting blocking onset with general circulation model (GCM) model is yet a very difficult task. Perhaps, the key point is that the physical mechanism leading to blocking formation remains unclear. The relationship between blocking waves and upstream synoptic-scale activity has attracted considerable attention from atmospheric scientists since it was first suggested by Berggren et al. [1949]. Numerous case studies indicate that the blocking flow configurations typically follow upstream cyclogenesis [Rex, 1950a[Rex, , 1950bGreen, 1977;Colucci, 1985Colucci, , 1987 Weak background westerlies as a precondition for block onset was first noted by Shutts [1983], who found that block does not occur for more rapid flows in which a stationary free state cannot be excited. However, Tsou and Smith [1990] and Colucci and Alberta [1996] suggested that the preconditioned planetary-scale ridge (incipient blocking ridge) may be another 31,795

Abstract. A proton transfer reaction ion-drift chemical ionization mass spectrometer (PTR-ID-CIMS) equipped with a hydronium (H + 3 O) ion source was developed and deployed near an industrial zone in the Yangtze River Delta (YRD) region of China in spring 2015 to investigate industryrelated emissions of volatile organic compounds (VOCs). Air pollutants including formaldehyde (HCHO), aromatics, and other trace gases (O 3 and CO) were simultaneously measured. Humidity effects on the sensitivity of the PTR-ID-CIMS for HCHO detection were investigated and quantified. The performances of the PTR-ID-CIMS were also validated by intercomparing with offline HCHO measurement technique using 2,4-dinitrophenylhydrazone (DNPH) cartridges and the results showed fairly good agreement (slope = 0.81, R 2 = 0.80). The PTR-ID-CIMS detection limit of HCHO (10 s, three-duty-cycle averages) was determined to be 0.9-2.4 (RH = 1-81.5 %) parts per billion by volume (ppbv) based on 3 times the standard deviations of the background signals. During the field study, observed HCHO concentrations ranged between 1.8 and 12.8 ppbv with a campaign average of 4.1 ± 1.6 ppbv, which was comparable with previous HCHO observations in other similar locations of China. However, HCHO diurnal profiles showed few features of secondary formation. In addition, time series of both HCHO and aromatic VOCs indicated strong influence from local emissions. Using a multiple linear regression fit model, on average the observed HCHO can be attributed to secondary formation (13.8 %), background level (27.0 %), and industryrelated emissions, i.e., combustion sources (43.2 %) and chemical productions (16.0 %). Moreover, within the plumes the industry-related emissions can account for up to 69.2 % of the observed HCHO. This work has provided direct evidence of strong primary emissions of HCHO from industryrelated activities. These primary HCHO sources can potentially have a strong impact on local and regional air pollution formation in this area of China. Given the fact that the YRD is the largest economic zone in China and is dense with petrochemical industries, primary industrial HCHO emissions should be strictly monitored and regulated.

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[1] The effects of aerosols on the development and precipitation for a mesoscale squall line occurring in the south plains of the United States have been investigated using a cloud-resolving Weather Research and Forecasting (CR-WRF) model with a two-moment bulk microphysical scheme. Different aerosol scenarios are considered in the CR-WRF model experiments, including polluted continental aerosols with a mean concentration of 2000 cm À3 . The simulated temporal evolution of composite radar reflectivity and the 24-h accumulated precipitation in the polluted aerosol experiment are in agreement with the measurements. The influence of aerosol concentrations is insignificant on the rainfall distribution but is remarkable on the precipitation intensity. The CR-WRF experiment with the polluted aerosol case predicts about 13% more precipitation and more locally intensive rainfall than do those with the clean aerosol case. Both the convection zone and the storm convective strength are increased in the polluted aerosol experiment in response to the increase in aerosol concentrations. The two-moment microphysical scheme is compared with three single-moment bulk schemes in the WRF model, including the Lin, WRF single-moment six-class, and Thompson schemes. Only the Thompson schemes reproduce the observed precipitation and radar reflectivity pattern, in agreement with the twomoment scheme with a leading convective line and a trailing stratiform precipitation regime. All of the single-moment schemes significantly overestimate the precipitation, especially with the Lin scheme, while the two-moment scheme yields the precipitation simulation comparable with the measurement.

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