Passage Of Cold Front Research Articles

Photochemical and meteorological relationships during the Texas-II Radical and Aerosol Measurement Project (TRAMP)

The Moody Tower measurement site at the University of Houston experienced several large ozone events during the Texas-II Radical and Aerosol Measurement Project (TRAMP) campaign between 13 Aug–02 Oct, 2006. This rooftop site samples that atmosphere 70 m a.g.l. and consequently is less susceptible to local surface emissions. Several high-ozone episodes encountered at Moody Tower during the TRAMP campaign were preceded one to two days earlier by a cold front passage, creating a situation where polluted air is transported from the North interacts with local Houston emissions and with light local winds. High quality CO measurements were good indicators of long range transport of pollution and/or biomass burning. During TRAMP there were also 4 periods with low “background” CO characterized by southerly winds, overcast conditions and low NOx and O 3 mixing ratios. The summer and fall of 2000 was an unusually hot period in Houston with considerably higher ozone levels than the 2000–2007 climatology. The 2006 TRAMP time period is more representative of the typical conditions for these 8 years. Over the time period from 1991 to 2009 the number of 8-h ozone episode days in Houston has decreased, as have the peak 1-h ozone mixing ratios. It is not possible from this analysis to demonstrate whether these improvements in Houston air quality are due to reductions in NOx levels, VOCs levels, and/or changes in meteorology.

Brazilian offshore wave climate based on NWW3 reanalysis

This paper provides a description of the wave climate off the Brazilian coast based on an eleven-year time series (Jan/1997-Dec/2007) obtained from the NWW3 operational model hindcast reanalysis. Information about wave climate in Brazilian waters is very scarce and mainly based on occasional short-term observations, the present analysis being the first covering such temporal and spatial scales. To define the wave climate, six sectors were defined and analyzed along the Brazilian shelf-break: South (W1), Southeast (W2), Central (W3), East (W4), Northeast (W5) and North (W6). W1, W2 and W3 wave regimes are determined by the South Atlantic High (SAH) and the passage of synoptic cold fronts; W4, W5 and W6 are controlled by the Intertropical Convergence Zone (ITCZ) and its meridional oscillation. The most energetic waves are from the S, generated by the strong winds associated to the passage of cold fronts, which mainly affect the southern region. Wave power presents a decrease in energy levels from south to north, with its annual variation showing that the winter months are the most energetic in W1 to W4, while in W5 and W6 the most energetic conditions occur during the austral summer. The information presented here provides boundary conditions for studies related to coastal processes, fundamental for a better understanding of the Brazilian coastal zone.

The Life Cycle of an Undular Bore and Its Interaction with a Shallow, Intense Cold Front

Abstract The evolution of an undular bore and its associated wind shift, spawned by the passage of a shallow surface cold front over the Southern Great Plains of the United States, is examined using surface and remote sensing observations along with output from a high-resolution numerical model simulation. Observations show that a separation between the wind shift and thermodynamic properties of the front was induced by the formation of a bore over south-central Kansas around 0200 UTC 29 November 2006. By the time the front–bore complex passed through Lamont, Oklahoma, approximately 4 h later, the bore had reached its maximum intensity and its associated wind shift preceded the trailing baroclinic zone by 20 min. Within several hours the bore decayed and a cold frontal passage, characterized by a wind shift coincident with thermodynamic properties was observed at Okmulgee, Oklahoma. Thus, a substantial transformation in both the structural and dynamical characteristics of the bore as well as its relationship to the parent surface front occurred during a short period of time. The details of this evolution are examined using output from a finescale numerical simulation, performed using the Weather Research and Forecasting (WRF) model. Analysis of the output reveals that as the bore advanced southeastward it moved into a region with a weaker surface stable layer. Consequently, the wave duct that had supported its maintenance steadily weakened resulting in dissipation of the bore. This circumstance led to a merger of the surface temperature and moisture boundaries with the orphaned wind shift, resulting in the cold frontal passage observed at Okmulgee.

Relationships between sudden weather changes in summer and mortality in the Czech Republic, 1986–2005

The study examines the relationship between sudden changes in weather conditions in summer, represented by (1) sudden air temperature changes, (2) sudden atmospheric pressure changes, and (3) passages of strong atmospheric fronts; and variations in daily mortality in the population of the Czech Republic. The events are selected from data covering 1986-2005 and compared with the database of daily excess all-cause mortality for the whole population and persons aged 70 years and above. Relative deviations of mortality, i.e., ratios of the excess mortality to the expected number of deaths, were averaged over the selected events for days D-2 (2 days before a change) up to D+7 (7 days after), and their statistical significance was tested by means of the Monte Carlo method. We find that the periods around weather changes are associated with pronounced patterns in mortality: a significant increase in mortality is found after large temperature increases and on days of large pressure drops; a decrease in mortality (partly due to a harvesting effect) occurs after large temperature drops, pressure increases, and passages of strong cold fronts. The relationship to variations in excess mortality is better expressed for sudden air temperature/pressure changes than for passages of atmospheric fronts. The mortality effects are usually more pronounced in the age group 70 years and above. The impacts associated with large negative changes of pressure are statistically independent of the effects of temperature; the corresponding dummy variable is found to be a significant predictor in the ARIMA model for relative deviations of mortality. This suggests that sudden weather changes should be tested also in time series models for predicting excess mortality as they may enhance their performance.

Compatibility between modes of low‐frequency variability and circulation types: A case study of the northwest Iberian Peninsula

Modes of low‐frequency variability have a major influence on the variability of the climate system at different temporal and spatial scales. Although the North Atlantic Oscillation explains a substantial portion of the climate variability in Europe, it is also necessary to consider other modes of low‐frequency variability, such as the Scandinavian index, the eastern Atlantic or the eastern Atlantic/western Russia indices. Furthermore, the relationship between the modes of low‐frequency variability and the climate in Europe cannot be considered to be stable over time. The aim of this paper is to assess the compatibility between the modes of low‐frequency variability in Europe (computed using a principal component analysis (PCA)) and local circulation regimes (using an automated version of the Lamb weather‐type classification), thus to observe how shifts in the positions of the modes of low‐frequency variability in Europe, could affect local circulation. Our study area (NW Iberian Peninsula) was chosen because it is characterized by the passage of cold fronts associated with the storm track in the North Atlantic Ocean and is sensitive to any variability in precipitation and temperature that is linked to the main North Atlantic modes of low‐frequency variability. The results show that there is a high degree of correlation between regional modes of low‐frequency variability derived from a statistical approach (using PCA) and real physical circulations (as represented by circulation types). Furthermore, changes in the position of modes of low‐frequency variability tend to favor some circulation types over others.

Strong wind climatic zones in South Africa

In this paper South Africa is divided into strong wind climate zones, which indicate the main sources of annual maximum wind gusts. By the analysis of wind gust data of 94 weather stations, which had continuous climate time series of 10 years or longer, six sources, or strong-wind producing mechanisms, could be identified and zoned accordingly. The two primary causes of strong wind gusts are thunderstorm activity and extratropical low pressure systems, which are associated with the passage of cold fronts over the southern African subcontinent. Over the eastern and central interior of South Africa annual maximum wind gusts are usually caused by thunderstorm gust fronts during summer, while in the western and southern interior extratropical cyclones play the most dominant role. Along the coast and adjacent interior annual extreme gusts are usually caused by extratropical cyclones. Four secondary sources of strong winds are the ridging of the quasi-stationary Atlantic and Indian Ocean high pressure systems over the subcontinent, surface troughs to the west in the interior with strong ridging from the east, convergence from the interior towards isolated low pressure systems or deep coastal low pressure systems, and deep surface troughs on the West Coast.

The ultrafine particles over the southern mid-latitude Indian Ocean — wind-generated or advected down with subsidence?

Concentration and number size distribution of aerosol particles from 4.4 to 168 nm diameter are measured at ten latitudinal positions in the Indian Ocean during the Pilot Expedition to Southern Ocean (PESO) from January 23 to March 31, 2004. Total number concentration of particles is minimum in the southern tropical trade wind region and maximum in the roaring forties. Number size distributions follow the power law over the northern Indian Ocean but are monomodal with the maxima lying between 35 and 60 nm over the southern Indian Ocean. Particles of diameter as small as 5 nm are observed in concentrations of ∼ 10 3 cm − 3 in the roaring forties (e.g. ∼ 40–50°S). Concentration of particles of < 50 nm diameter increases with wind speed. Thus, in addition to the ultrafine and Aitken mode particles being transported from the free troposphere to the marine boundary layer with the subsidence following cold frontal passages in the southern mid-latitudes, the wind-generated particles significantly contribute to the ultrafine aerosols down to 5 nm diameter in the roaring forties. Observations indicate that while the wind-generated particles dominate at ∼ 45°S, the particles associated with the subsidence dominate at ∼ 38°S.

風力発電出力予測への気象モデルの相互比較

The objective of this study is to investigate the differences in accuracies of wind predictions among four different meso scale meteorological models that will be used to develop a wind power prediction model. Hindcasts of winds are carried out using these models for four wind farms (three in Tohoku and one in Kanto districts). The performances of the models are discussed by comparing the simulated results with the wind data observed at these wind farms under different meteorological conditions. The results show that the meteorological models exhibit similar tendencies for general meteorological cases. On the other hand, significant differences are found in some cases such as those characterized by the passages of cold fronts, typhoons, and so on. The evaluations of the uncertainties in the meteorological model predictions show that the individual models have uncertainties of approximately 3 m/s in wind speed and 40° in wind direction. Additionally, the results also indicate that uncertainties attributable to the differences of the model design amount to only 10% of the total uncertainties, and that the initial and boundary conditions as well as the formulations of the models themselves can have more significant effects on the prediction accuracies.

Mountain accidents associated with winter northern flows in the Mediterranean Pyrenees

The Mediterranean Pyrenees, at the eastern end of the range, is a very popular area. Its highestpeak is at 2900 m a.s.l. and there are numerous peaks above 2000 m, with rounded relief andsparse vegetation on the latter height. One of its significant winter climatic features is the sud-den entrance of cold air with violent northern winds, drop in temperatures and very low windchill values. Such advections are established after the passage of a snowy cold front and, con-sequently, there is abundant transport of both new and existing snow that reduces horizontalvisibility. The post-frontal conditions at high altitudes represent a serious threat to humans. Thereview done shows that the hikers immersed in an environment of low visibility, strong windsand very low temperatures can quickly become disoriented, suffer frostbite and hypothermia andslip on the ice. The characterization of a series of accidents occurred in this geographical area,identified in the press, shows in this paper that the phenomena associated with northern win-ter advections is an element of danger to be considered in the evaluation of natural hazards inthat area. In addition, the multiple character of many of the events suggests that there is highvulnerability to such dangers. The climatological analysis presented suggests that such weatherconditions are not uncommon in the winter, although the most serious accidents have been reg-istered under especially strong and cold flows. The conclusions recommend that the weatherconditions described, locally called torb, should be known by the visitors to these mountains inthe winter, and its appearance should be announced in weather reports, which in turn must besufficiently disseminated in the areas of greater abundance of tourists and hikers.

GPS Zenith Total Delays and Precipitable Water in comparison with special meteorological observations in Verona (Italy)during MAP-SOP

Continuous meteorological examination of the Pre-Alpine zones in Northern Italy (Po Valley) is important for determination of atmospheric water cycles connected with floods and rainfalls. During a special meteorological observing period (MAP-SOP), radiosounding and other measurements were made in the site of Verona (Italy). This paper deals with Zenith Total Delay (ZTD) and Precipitable Water (PW) comparisons obtained by GPS, radiosounding and other meteorological measurements. PW and ZTD from ground-based GPS data in comparison with classical techniques (e.g., WVR, radiosounding) from recent literature present an accurate tool for use in meteorology applications (e.g., assimilation in Numerical Weather Prediction (NWP) models on short-range precipitation forecasts). Comparison of such ZTD for MAP-SOP showed a standard deviation of 16.1 mm and PW comparison showed a standard deviation of 2.7 mm, confirming the accuracy of GPS measurements for meteorology applications. In addition, PW data and its time variation are also matched with time series of meteorological situations. Those results indicate that changes in PW values could be connected to changes in air masses, i.e. to passages of both cold and warm fronts. There is also a correlation between precipitation, forthcoming increase and the following decrease of PW. A good agreement between oscillation of PW and precipitation and strong cyclonic activities is found.

Impact of climate on the vertical water column structure of Lajes Reservoir (Brazil): A tropical reservoir case

AbstractRibeirão das Lajes Reservoir was constructed in 1905 for energy production, and is now used as a domestic water supply for about 1 million people. The reservoir was considered as being general monomictic, exhibiting water column mixing in the winter. Water column mixing, however, did not occur in the deepest parts of the reservoir in the warm year of 2005. Nevertheless, the long stratification period leads to an anoxic, nutrient‐rich hypolimnion that exhibits poor water quality in the deepest part. The meteorological events of cold front passages in the reservoir region were not able to disrupt the water column stability, or affect its water quality for domestic supply. Maintenance of thermal stratification over most of the year was likely because of the low influence of wind, long water retention time, and the input of cold water from the tributary and from rain directly draining into the metalimnion.

The effect of environmental factors on floating fresh marsh end-of-season biomass

We used both stepwise and quantile regression to determine the sources of environmental variation that explained the observed inter-annual variation in end-of-season freshwater floating marsh aboveground biomass over an 18-year period. The vegetation at our study site had high species diversity with an average of 20 species recorded from 10 0.25 m −2 plots. However, Panicum hemitomon was clearly the dominant contributing 74% of the total biomass. Only three other species ( Solidago sempervirens, Vigna luteola, and Thelypteris palustris) were so common that they were sampled in all years. We expected that the most important factors controlling interannual variation in aboveground biomass are temperature and nitrogen availability. We also expected that nitrogen availability to the plants is affected by water movement through and under the mat driven by precipitation (lower N), evaporation (transportation of higher N waters to roots), and local runoff (higher N). Stepwise regression analysis indicated that P. hemitomon average biomass was negatively related to average water level and positively related to maximum water level and had a curvilinear response with TKN. Using quantile regression the best fit for P. hemitomon maximum-biomass with two parameters was obtained using hot days (positive relationship) and maximum water level (negative relationship). Both analytical methods showed maximum water level (negative relationship) and cold front passage (positive relationship) to be the environmental parameters that best explained interannual variation in S. sempervirens biomass. V. luteola biomass was positively related to temperature. Stepwise regression added chloride concentration as an additional positive parameter explaining V. luteola biomass, while quantile regression identified nitrogen as an important positive parameter. Both analytical methods identified pH, TKN, and water level as environmental parameters that were negatively correlated with T. palustris biomass. The overall negative effect of water level on all species was unexpected in this floating mat system. We initially assumed that higher water levels were due to higher runoff which should have a positive effect on biomass. However, higher water levels may also be related to a higher retention time in this fresh-water tidal system, which decreases water exchange and nutrient replenishment.

Effect of cold fronts on the benthic macrofauna of exposed sandy beaches with contrasting morphodynamics

The aim of this study was to determine the short-term environmental changes caused by the simultaneous passage of a high energy event on two sandy beaches with different morphodynamic states and their influence on the richness, abundance and distribution of the benthic macrofauna. Two microtidal exposed sandy beaches with contrasting morphodynamics were simultaneously sampled before, during and after the passage of two cold fronts in Santa Catarina. The reflective beach showed a higher susceptibility to the increase in wave energy produced by the passage of cold fronts and was characterized by rapid and intense erosive processes in addition to a capacity for rapid restoration of the beach profile. As regards the dissipative beach, erosive processes operated more slowly and progressively, and it was characterized further by a reduced capacity for the recovery of its sub-aerial profile. Although the intensity of the environmental changes was distinct as between the morphodynamic extremes, changes in the composition, richness and abundance of macrobenthos induced by cold fronts were not evident for either of the beaches studied. On the other hand, alterations in the distribution pattern of the macrofauna were observed on the two beaches and were related to variations in sea level, position of the swash zone and moisture gradient, suggesting that short-term accommodations in the spatial structure of the macrobenthos occur in response to changes in environmental conditions in accordance with the temporal dynamics characteristic of each morphodynamic state.

Discrete Frontal Propagation over the Sierra–Cascade Mountains and Intermountain West

Abstract On 25 March 2006, a complex frontal system moved across the Sierra–Cascade Mountains and intensified rapidly over the Intermountain West where it produced one of the strongest cold-frontal passages observed in Salt Lake City, Utah, during the past 25 yr. Observational analyses and numerical simulations by the Weather Research and Forecast (WRF) Model illustrate that the frontal system propagated discretely across the Sierra–Cascade Mountains and western Nevada. This discrete propagation occurs in a synoptic environment that features a mobile upper-level cyclonic potential vorticity (PV) anomaly that is coupled initially with a landfalling Pacific cyclone and attendant occluded front. The eastward migration of the upper-level cyclonic PV anomaly ultimately encourages the development of a new surface-based cold front ahead of the landfalling occlusion as troughing, confluence, and convergence downstream of the Sierra Nevada intensify preexisting baroclinity over Nevada. Trajectories show that the new cold front represents a boundary between potentially warm air originating over the desert Southwest, some of which has been deflected around the south end of the high sierra, and potentially cool air that has traversed the sierra near and north of Lake Tahoe, some of which has been deflected around the north end of the high sierra. Although diabatic processes contribute to the frontal sharpening, they are not needed for the discrete propagation or rapid cold-frontal development. Forecasters should be vigilant for discrete frontal propagation in similar synoptic situations and recognize that moist convection or differential surface heating can contribute to but are not necessary for rapid Intermountain West frontogenesis.

Wave‐mud interactions over the muddy Atchafalaya subaqueous clinoform, Louisiana, United States: Wave‐supported sediment transport

Near‐bottom fluid‐mud layers were observed during two experiments conducted on the muddy Atchafalaya inner shelf (subaqueous clinoform), Louisiana, United States. On the face of the subaqueous delta (4–7 m water depth, first experiment) fluid‐mud layers are produced by seafloor liquefaction and resuspension forced by swells associated with cold front passages, and supported by near‐bed wave‐induced turbulence. The layers are episodic (lifetime of 9–12 h), form prior to significant postfrontal settling of sediment in the overlying water column, and flow seaward (downslope) at about 5 cm/s. Farther westward on the delta front (finer grain size, with negligible sand or coarse silt content, second experiment), similar wave‐supported fluid‐mud layers are observed to last longer (&gt;2 days), show weaker alongshore (westward) flow of about 1–3 cm/s. The results suggest a sequence of near‐bed sediment transport processes, triggered by frontal swell activity (bed liquefaction, resuspension and advection, modulated by the bathymetric characteristics of the clinoform) that contribute to the formation of clinoform stratigraphy of muddy subaqueous deltas.

The European storm Kyrill in January 2007: synoptic evolution, meteorological impacts and some considerations with respect to climate change

Abstract. The synoptic evolution and some meteorological impacts of the European winter storm Kyrill that swept across Western, Central, and Eastern Europe between 17 and 19 January 2007 are investigated. The intensity and large storm damage associated with Kyrill is explained based on synoptic and mesoscale environmental storm features, as well as on comparisons to previous storms. Kyrill appeared on weather maps over the US state of Arkansas about four days before it hit Europe. It underwent an explosive intensification over the Western North Atlantic Ocean while crossing a very intense zonal polar jet stream. A superposition of several favourable meteorological conditions west of the British Isles caused a further deepening of the storm when it started to affect Western Europe. Evidence is provided that a favourable alignment of three polar jet streaks and a dry air intrusion over the occlusion and cold fronts were causal factors in maintaining Kyrill's low pressure very far into Eastern Europe. Kyrill, like many other strong European winter storms, was embedded in a pre-existing, anomalously wide, north-south mean sea-level pressure (MSLP) gradient field. In addition to the range of gusts that might be expected from the synoptic-scale pressure field, mesoscale features associated with convective overturning at the cold front are suggested as the likely causes for the extremely damaging peak gusts observed at many lowland stations during the passage of Kyrill's cold front. Compared to other storms, Kyrill was by far not the most intense system in terms of core pressure and circulation anomaly. However, the system moved into a pre-existing strong MSLP gradient located over Central Europe which extended into Eastern Europe. This fact is considered determinant for the anomalously large area affected by Kyrill. Additionally, considerations of windiness in climate change simulations using two state-of-the-art regional climate models driven by ECHAM5 indicate that not only Central, but also Eastern Central Europe may be affected by higher surface wind speeds at the end of the 21st century. These changes are partially associated with the increased pressure gradient over Europe which is identified in the ECHAM5 simulations. Thus, with respect to the area affected, as well as to the synoptic and mesoscale storm features, it is proposed that Kyrill may serve as an interesting study case to assess future storm impacts.

Influence of Surface-Based Stable Layer Development on Asian Dust Behaviour Over Tokyo

The relationship between local meteorological fields and the behaviour of airborne Asian dust that arrived in the Tokyo metropolitan area on 1 April 2007 with the passage of a synoptic-scale cold front has been investigated through Doppler lidar observations, experiments using a regional atmospheric numerical model, and analyses of surface and upper-air meteorological observations. Results of the Doppler lidar observations showed that the Asian dust passed above the metropolitan area with strong south-westerly winds with speeds of 15–26 m s−1. Meteorological fields reproduced by the numerical experiments showed the development of a surface-based stable layer in the metropolitan area caused by nocturnal radiational cooling near the ground surface and south-westerly warm air advection at upper levels. The blocking effect of the mountainous region located to the west of the metropolitan area induced an area of stagnant air inside the metropolitan area and promoted the stable layer development. Although strong downdrafts prevailed in the upper air, the airborne Asian dust did not spread to the ground when the stable layer was formed. These results strongly indicate that the developed stable layer prevented strong downdrafts from spreading to the ground, acting as an obstacle to the transport of the Asian dust particles from the upper air towards the ground. This is considered to be one of the main causes of the low appearance frequency of Asian dust phenomena near the ground in the Tokyo metropolitan area and eastern Japan.

Eddy covariance measurements of surface energy budget and evaporation in a cool season over southern open water in Mississippi

Eddy covariance measurements of sensible (H) and latent (LE) heat fluxes were made over a large southern open water surface of Ross Barnett Reservoir (the Reservoir hereafter) in Mississippi during the cool season with frequent incursions of cold fronts from 1 September 2007 to 31 January 2008. The eddy covariance tower was located in the middle of the main body of the Reservoir with the tower fetches exceeding 2.0 km in all directions. The Reservoir was ice‐free in winter and the water temperatures always decreased with depth. Over the entire cool season, the averaged water surface temperatures were 1.8°C higher than the overlying air (i.e., positive temperature gradients that led to thermally convective conditions) and the averaged vapor pressure near the water surface was 0.8 kPa greater than the overlying air (i.e., positive vapor pressure gradients), though occasionally negative gradients for temperature and vapor pressure were also observed for short periods. On average, the wind speeds were considerably large (3.9 m s−1) to maintain adequate turbulent mixing mechanically. As a consequence of the combined effect of thermally and mechanically generated turbulent mixing, consistently positive H (with a mean H of 20.0 W m−2) and LE (with a mean LE of 80.0 W m−2) occurred during the entire season. These continuous energy losses via H and LE resulted in release of a large amount of energy stored in the water to the atmosphere. The mean Bowen ratio was low for this open water surface (i.e., 0.3), suggesting that most of the energy released from the water fueled evaporation rather than sensible heating of the atmosphere. Nighttime evaporative water losses were substantial, contributing to 45% of the total evaporative water loss in this cool season. Frequent incursions of cold fronts with windy, cold, and dry air masses significantly promoted turbulent exchanges of sensible and latent heat through enhanced turbulent mixing thermally and mechanically, leading to large H and LE events. Daily H and LE (i.e., evaporation) during the passages of cold fronts were on average 2.7 and 7.3 times those in nonevent days, respectively. Given the fact that large H and LE events occurred 26% of the time for our site, these cold front events caused an increase in the seasonal H by 42% and LE by 157%. Therefore changes in frequency, intensity, and duration of synoptic weather events, particularly the incursions of cold fronts, have significant impacts on the surface energy budget and evaporation over water at this site.

Spatial and temporal variations of aerosols around Beijing in summer 2006: Model evaluation and source apportionment

Regional aerosol model calculations were made using the Weather Research and Forecasting (WRF)‐Community Multiscale Air Quality (CMAQ) and WRF‐chem models to study spatial and temporal variations of aerosols around Beijing, China, in the summer of 2006, when the Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing) intensive campaign was conducted. Model calculations captured temporal variations of primary (such as elemental carbon (EC)) and secondary (such as sulfate) aerosols observed in and around Beijing. The spatial distributions of aerosol optical depth observed by the MODIS satellite sensors were also reproduced over northeast China. Model calculations showed distinct differences in spatial distributions between primary and secondary aerosols in association with synoptic‐scale meteorology. Secondary aerosols increased in air around Beijing on a scale of about 1000 × 1000 km2 under an anticyclonic pressure system. This air mass was transported northward from the high anthropogenic emission area extending south of Beijing with continuous photochemical production. Subsequent cold front passage brought clean air from the north, and polluted air around Beijing was swept to the south of Beijing. This cycle was repeated about once a week and was found to be responsible for observed enhancements/reductions of aerosols at the intensive measurement sites. In contrast to secondary aerosols, the spatial distributions of primary aerosols (EC) reflected those of emissions, resulting in only slight variability despite the changes in synoptic‐scale meteorology. In accordance with these results, source apportionment simulations revealed that primary aerosols around Beijing were controlled by emissions within 100 km around Beijing within the preceding 24 h, while emissions as far as 500 km and within the preceding 3 days were found to affect secondary aerosols.

Synoptic patterns associated with landslide events in the Serra do Mar, Brazil

Heavy rains frequently occur over the Serra do Mar, in the southeast coastal mountain region in Brazil, particularly during the summer season. These rains can cause landslides and loss of life. The objective of this work is to produce a synoptic climatology of heavy rainfall episodes of the period from November to April using 10-year reanalyses data. The identification of the synoptic pattern of these events should provide guidance to forecasters. The landslide events were mostly related to cold front passages and the South Atlantic Convergence Zone (SACZ). These systems differed from the climatology by exhibiting more intense characteristics for the frontal situations and a blocking circulation configuration for the SACZ situations. In both cases, the composite fields showed that the 250-hPa mass divergence was strikingly more intense than the climatology and had a preferred location in the 24 h prior to landslide events. Anomalies of this ten-year event climatology showed above-normal moisture anomalies, which are more evident in the SACZ than in the frontal cases.