Influence Of Cold Fronts Research Articles

High O3 pollution initiated by cold front passage over Pearl River Estuary

The influence of cold fronts on the formation of ozone (O3) pollution, particularly the contributions of physical and chemical processes to O3 abundance during the passage of cold fronts in winter over the Pearl River Estuary (PRE) region was still unclear. This study provided an in-depth analysis on the occurrence of high O3 pollution based on data from field measurements and simulation of a chemical transport model (i.e., WRF-Chem) over the PRE region during winter 2021 when cold fronts were frequently observed. Totally 7 high O3 episode days were observed during pre- and post-frontal stages at DWS (i.e., Da Wan Shan island), a downwind island site of the inland Pearl River Delta (PRD) region, which were accompanied with the prevailing northerly wind patterns with insignificant variations of wind speeds in a stable boundary layer over the whole PRE region. The quantitative analysis based on simulation results indicated that horizontal transport and chemical processes accounted for the buildup of O3 abundance at DWS, with the highest mean rates of 7.3 and 5.6 ppbv/h at pre- and post-frontal stages, respectively. The high contributions from horizontal transport to O3 levels at DWS were associated with the persistent northerly winds with small variations, while the contributions of chemical processes were varied with the abundance of precursors and meteorological conditions. However, vertical transport made negative contributions to O3 abundance, with the most significant mean diffusion rate of −2.6 ppbv/h at the frontal stage because of the control of high-pressure system, while the less influence of vertical transport at pre- and post-frontal stages was associated with the weak pressure gradient forces and wind patterns. The sensitivity analysis further demonstrated that the emissions of precursors from the inland PRD region contributed 50–76% to O3 abundance over PRE at different stages. Overall, the above results quantitatively confirmed the dominant role of transport from inland PRD to the O3 pollution over the downwind PRE region and were helpful for better understanding of O3 pollution in winter over PRE.

Influence of cold fronts on microscale atmospheric conditions within the complex terrain of Watkins Glen Gorge, New York

ABSTRACT This study investigates the influence of synoptic-scale cold fronts on microclimatic conditions within the complex terrain of Watkins Glen gorge, New York. Temperature and dewpoint temperature measurements were collected by three microclimate stations both within (two stations) and just outside (one station) of the gorge during the months of September and November. A total of nine cold fronts passed over the gorge at different times of day (i.e., daytime, nighttime, and transitional) during the eight-week measurement period. During the prefrontal time periods, the two sites within the gorge were similar in both temperature and moisture content: colder and greater moisture content compared to the outside-gorge site. A stable inversion layer was present at the rim height of the gorge a large percentage of time resulting in limited mixing and a separation of the outside-gorge and inside-gorge atmospheres. Following the passage of cold fronts, there was a robust transition to a large-scale colder atmospheric air mass across the central New York region and introduction of less stable conditions that allowed intrusion and mixing of outside-gorge air within the complex terrain of Watkins Glen gorge, especially during nighttime and transitional cold fronts.

Measurement report: Ice nucleating abilities of biomass burning, African dust, and sea spray aerosol particles over the Yucatán Peninsula

Abstract. Most precipitation from deep clouds over the continents and in the intertropical convergence zone is strongly influenced by the presence of ice crystals whose formation requires the presence of ice nucleating particles (INPs). Although there are a large number of INP sources, the ice nucleating abilities of aerosol particles originating from oceans, deserts, and wildfires are poorly described at tropical latitudes. To fill this gap in knowledge, the National Autonomous University of Mexico micro-orifice uniform deposit impactor droplet freezing technique (UNAM-MOUDI-DFT) was constructed to measure the ice nucleating activity of aerosol samples that were collected in Sisal and Mérida, Yucatán (Mexico) under the influence of cold fronts, biomass burning (BB), and African dust (AD) intrusions during five short-term field campaigns between January 2017 and July 2018. The three different aerosol types were distinguished by their physicochemical properties. Marine aerosol (MA), BB, and AD air masses were found to contain INPs; the highest concentrations were in AD (from 0.071 to 36.07 L−1 at temperatures between −18 and −27 ∘C), followed by MA (from 0.068 to 18.90 L−1 at temperatures between −15 and −28 ∘C) and BB (from 0.063 to 10.21 L−1 at temperatures between −20 and −27 ∘C). However, MA had the highest surface active site densities (ns) between −15 and −30 ∘C. Additionally, supermicron particles contributed more than 72 % of the total INP concentration independent of aerosol type.

Secondary aerosol formation and its linkage with synoptic conditions during winter haze pollution over eastern China

Eastern China has been facing severe winter haze pollution due mainly to secondary aerosol. Existing studies have suggested that stagnant weather or fast chemical production led to frequent haze in this region. However, few works focus on the linkage between secondary production of sulfate, nitrate, and ammonium (SNA) and synoptic conditions, and their joint contribution to PM2.5. In this study, by combining in-situ measurements on meteorology and aerosol chemical composition at three main cities together with a regional model with improved diagnose scheme, we investigated the chemical formation and accumulation of main secondary composition, i.e. SNA under typical synoptic conditions. It is indicated that SNA did play a vital role in haze pollution across eastern China, contributing more than 40% to PM2.5 mass concentration. As most fast developing region, the Yangtze River Delta (YRD) was slightly polluted during stable weather with local chemical production accounting for 61% SNA pollution. While under the influence of cold front, the pollution was aggravated and advection transport became the predominant contributive process (85%). Nevertheless, the chemical production of SNA was notably enhanced due to the uplift of air pollutant and elevated humidity ahead of the cold front, which then facilitated the heterogeneous and aqueous-phase oxidation of precursors. We also found the substantial difference in the phase equilibrium of nitrate over the land surface and ocean due to changes in temperature, ammonia availability and dry deposition. This study highlights the close link between synoptic weather and chemical production, and the resultant vertical and spatial heterogeneity of pollution.

Influence of Cold Fronts on Variability of Daily Surface O3 over the Houston-Galveston-Brazoria Area in Texas USA during 2003–2016

We investigated the impacts of cold fronts on area-wide peak O3 and regional backgroundO3 mixing ratios on a daily scale over the Houston-Galveston-Brazoria (HGB) area of southeasternTexas during the O3 seasons (April–October) of 2003–2016. Back trajectories showed that an 18h timelag existed between arrival of cold fronts in the HGB area and onset of a predominately northerlyflow. Cold fronts showed increasing effects on both peak and background O3 over the HGB area.Compared to no front days, average peak O3 mixing ratios during the cold front 1st days, coldfront 2+ days, and post frontal days increased 0.7, 5.9, and 9.0 ppbv, respectively while averagebackground O3 increased 2.9, 6.8, and 8.6 ppbv, respectively. The change in wind direction fromsoutherly to northerly was the most important factor causing increasing O3 levels. Wind directionshifts caused variation of other meteorological factors (i.e., wind speed, precipitation, temperature,cloud cover, and relative humidity) and tended to overshadow their effects on O3 over the HGB area.On a long-term and large-scale view, cold fronts over the HGB area could be regarded as interruptionsin the cleansing effects of predominantly marine southerly flow from the Gulf of Mexico.

Effects of the large-scale atmospheric circulation on the onset and strength of urban heat islands: a case study

Air temperature was monitored at 13 sites across the urban perimeter of a Brazilian midsize city in winter 2011. In this study, we show that the urban heat island (UHI) develops only at night and under certain weather conditions, and its intensity depends not only on the site's land cover but also on the meteorological setting. The urban heat island intensity was largest (6.6 °C) under lingering high-pressure conditions, milder (3.0 °C) under cold anticyclones and almost vanished (1.0 °C) during the passage of cold fronts. The cooling rates were calculated to monitor the growth and decay of the UHI over each specific synoptic setting. Over four contiguous days under the effect of a lingering high-pressure event, we observed that the onset of cooling was always at about 2 h before sunset. The reference site attained mean cooling rate of −2.6 °C h−1 at sunset, whilst the maximum urban rate was −1.2 °C h−1. Under a 3-day cold anticyclone episode, cooling also started about 2 h before sunset, and the difference between maximum rural (−2.0 °C h−1) and urban (−1.0 °C h−1) cooling rates diminished. Under cold-front conditions, the cooling rate was homogeneous for all sites and swang about zero throughout the day. The air temperature has a memory effect under lingering high-pressure conditions which intensified the UHI, in addition to the larger heat storage in the urban area. Cold anticyclone conditions promoted the development of the UHI; however, the cold air pool and relatively light winds smoothed out its intensity. Under the influence of cold fronts, the urban fabric had little effect on the city's air temperature field, and the UHI was imperceptible.

Influence of different weather events on concentrations of particulate matter with different sizes in Lanzhou, China

AbstractThe formation and development of weather events has a great impact on the diffusion, accumulation and transport of air pollutants, and causes great changes in the particulate pollution level. It is very important to study their influence on particulate pollution. Lanzhou is one of the most particulate-polluted cities in China and even in the world. Particulate matter (PM) including TSP, PM>10, PM2.5–10, PM2.5 and PM10 concentrations were simultaneously measured during 2005–2007 in Lanzhou to evaluate the influence of three kinds of weather events – dust, precipitation and cold front – on the concentrations of PM with different sizes and detect the temporal evolution. The main results are as follows: (1) the PM pollution in Lanzhou during dust events was very heavy and the rate of increase in the concentration of PM2.5–10 was the highest of the five kinds of particles. During dust-storm events, the highest peaks of the concentrations of fine particles (PM2.5 and PM10) occurred 3 hr later than those of coarse particles (PM>10 and PM2.5–10). (2) The major effect of precipitation events on PM is wet scavenging. The scavenging rates of particles were closely associated with the kinds of precipitation events. The scavenging rates of TSP, PM>10 and PM2.5–10 by convective precipitation were several times as high as those caused by frontal precipitation for the same precipitation amount, the reason being the different formation mechanism and precipitation characteristics of the two kinds of precipitation. Moreover, there exists a limiting value for the scavenging rates of particles by precipitation. (3) The major effect of cold-front events on particles is clearance. However, during cold-front passages, the PM concentrations could sometimes rise first and decrease afterwards, which is the critical difference in the influence of cold fronts on the concentrations of particulate pollutants vs. gaseous pollutants.

Opady frontowe na polskim wybrzeżu Bałtyku

The climate of the Baltic coastline is strongly affected by prevailing cyclones and frontal activities. Frontal precipitation is shown to dominate in the Baltic area, with about two–thirds of rainfall events being frontal in origin (Walther and Bennartz, 2006). The aim of the work described here was to study precipitation totals in relation to selected atmospheric fronts and days without fronts. The analysis took in the daily precipitation totals recorded during both the cold seasons (October–March) and the warm ones (April-September) in the years 1998–2003, at seven stations along the Baltic coast (i.ee. Szczecin, Świnoujście, Koszalin, Łeba, Hel, Gdynia and Elbląg). The lower weather charts from the years 1998–2003 published by wetterzentrale (www.wetterzentrale.de/topkarten) formed a basis upon which to state the occurrence of different kinds of fronts. Irrespective of kind, the occurrence of a front causes an increase in precipitation totals, while there is a decrease on days without fronts (Table 1). The t-Student test shows that the influence of cold fronts on the precipitation pattern is more important in a warm season than in a cold one, while the effect of warm fronts is greater in a cold season. The highest mean daily precipitation totals along the Polish coast relate to the passage of an occluded front (Tab. 1, Tab. 2). Extreme high totals for precipitation are associated with cold fronts. There are single events with very high totals on days without fronts (Fig. 1) – 27.1 mm was the maximum daily precipitation total (mean for seven stations) recorded for days analyzed in the study. It was noted on September 13th 1999 and was associated with convective rainfall in conditions of a barometric trough. The breakdown of precipitation totals was also studied by size category, with the frequency of occurrence of daily totals within selected size intervals being presented (Fig. 2). The most frequent daily totals were of between 0.01 and 0.50 mm. The probability of moderate precipitation totals (in the 1.01–5.00 range) is higher in the presence of occluded fronts than when warm or cold fronts are passing through. Mean numbers of stations experiencing precipitation as selected fronts pass through were also calculated, as was the frequency of occurrence of precipitation at all stations in days with or without fronts (Figs. 3, 4).

Seabirds attending bottom long‐line fishing off southeastern Brazil

Flocks of seabirds attending commercial bottom long‐line fishing operations on the coastal shelf off southeastern Brazil show a greater species diversity during the summer than the winter (16 v 9 species), although the number of birds per flock tended to be greater during the cold season. During the summer, the Spectacled Petrel Procellaria aequinoctialis conspi‐cillata was the commonest species, followed by the Great Shearwater Puffinus gravis, Cory's Shearwater Calonectris diomedea, skuas Stercorarius spp. and the Yellow‐nosed AlbatrossDiomedea chlororhynchus. During the winter, the White‐chinned Petrel Procellaria aequin‐octialis, Yellow‐nosed Albatross and Black‐browed Albatross Diomedea melanophrys were jointly the commonest species. Marked differences in the relative abundance of species were observed between the different sampling periods, probably because of migratory movements but also because of seasonal shifts of the sea currents and the influence of cold fronts. Waters off southeastern Brazil are important feeding areas for some seabird populations nesting in the Tristan da Cunha and Gough group, especially for nonbreeding Spectacled Petrels and post‐breeding Yellow‐nosed Albatrosses.

Influence of a cold front upon the onset of Meniére's disease in Toyama, Japan.

In order to clarify the influence of a cold front (CF) upon the onset of Meniére's disease (MD), major CFs were defined by meteorological observations, and the influence of CFs on MD was evaluated by using the time n method. From our preliminary study it was seen that the onset of MD had its highest incidence exactly on days where a CF passed by. Out of the patients with MD, sudden deafness (SD) and Bell's palsy (BP) who visited our neurotological clinic of the Toyama Medical and Pharmaceutical University from 1987 to 1992, 67 MD patients, 70 SD patients and 70 BP patients could clearly define the date of the onset of their disease, and were therefore selected for this epidemiological study. Thirty-six our of the 67 MD patients had the first attack on the day when a CF passed by or on the next day. The results obtained from these studies were as follows. i) The onset of MD was influenced by the passing of a CF, and this influence was more specific in MD than in SD or BP. ii) In the 36 CF influence MD patients, the majority were over the forty years, and their hearing level was worse than that of the other 31 MD patients during the observation periods.

Influence of a Cold Front upon the Onset of Meniere's Disease

The influence of a cold front (CF) on the onset of Meniere's disease was investigated. A major CF is difined by the meteorological observatory as fulfilling the following conditions: 1. falling temperature (>5 deg), 2. rising humidity, 3. strong wind more than 10 m/sec, 4. rain or snow, 5. thunder, 6. wind shifting from south to north-west. This occured 14 times in 1992. The passing of a minor CF is decided from weather maps. Major and minor CFs occured oneclench for five days in winter and for 10 days in summer.The influence of CFs on Meniere's disease was evaluated by the time n method and the results were compared with those of patients with sudden deafness and with Bell's palsy.The onset of Meniere's disease had its highest incidence just after CF passed. The histogram of the number of days between the passing of a CF and the onset of Meniere's disease indicated a normal distribution. On the other hand, in patients with Bell's palsy the onset was most frequent one day before the passing of a CF, and in those with sudden deafness no specific concentration was observed.From these results we concluded that the onset of Meniere's disease was influenced by the passing of a CF and that this influence was more specific in Meniere's disease than in Bell's palsy or sudden deafness.