Analysis of the use of transformable elements in intelligent tunnel ventilation systems

All main and auxiliary equipment in the tunnel with an intelligent ventilation system are designed to ensure the safety. These systems “talk” and “listen” to each other, make decisions to switch on/off certain system(s) or part(s) thereof and duly inform the tunnel operator, who is authorized to the centralized control of all systems of necessity. The present article uses the numerical models to assess the efficiency of the transformable elements ensuring safe operation of the tunnels. The idea of their use is based on an artificial increase of the tunnel aerodynamic resistance by means of a flexible element, which will hamper the dissemination of combustion products, but not the movement of people through the tunnel and will help isolate clean and polluted air masses. Such resistance will be used to swiftly divide the tunnel carriageway into smaller sections what will help extinguish the fire as early as at its initial stage, prolong the evacuation time and save lives during the strong uncontrollable fires. As for the compact transformable element, it can be used in both, the operating and the planned tunnels, as it in practice does not reduce the volume of valuable underground space.

Simulation of the Multi-Timescale Stratospheric Intrusion Processes in a Typical Cut-Off Low over Northeast Asia

This study used the FLEXPART-WRF trajectory model to perform forward and backward simulations of a cut-off low (COL) event over northeast Asia. The analysis reveals the detailed trajectories and sources of air masses within the COL. Their trajectories illustrate the multi-timescale deep intrusion processes in the upper troposphere and lower stratosphere (UTLS) caused by the COL. The processes of air intrusion from the lower stratosphere to the middle troposphere can be divided into three stages: a slow descent stage, a rapid intrusion stage and a relatively slow intrusion stage. A source analysis of targeted air masses at 300 hPa and 500 hPa shows that the ozone-rich air in the COL primarily originated from an extratropical cyclone over central Siberia and from the extratropical jet stream. The sources of air masses in different parts of the COL show some differences. These results can help explain the ozone distribution characteristics in the main body of a COL at 300 hPa and at 500 hPa that were revealed in a previous study.

Influence of air masses on microphone vibration sensitivity

A study is presented of the primary design parameters that influence the vibration sensitivity of a microphone. The sensitivity to vibration is generally determined by the mass of the pressure-sensing diaphragm along with the mass of air that moves with it. The sound-sensing performance is improved as the pressure-sensing diaphragm is made thinner, but for a thin enough diaphragm, the moving air mass is not negligible relative to that of the diaphragm itself. In the present study, we develop a simple duct-acoustic model to account for the effect of the co-vibrating air. It is shown that an idealized massless, thin microphone diaphragm will still produce unwanted vibration signal due to acceleration of the air masses within the microphone. For a small microphone, the predicted pressure related acceleration sensitivity is found to be a simple function of the mass per unit area of the air inside of the microphone package. The acceleration sensitivity predicted using a finite element model of a one micrometer thick clamped flexible silicon diaphragm agrees with that predicted by the simple duct model. Measured and predicted acceleration sensitivities are compared for several MEMS and sub-miniature electret microphones of different back volume lengths . It is found that the primary design parameter determining vibration sensitivity for these microphones is the effective length of the column of air inside the microphone’s packaging. Microphones that have longer air-filled volumes had greater pressure related acceleration sensitivity.

Synoptic control over winter snowfall variability observed in a remote site of Apennine Mountains (Italy), 1884–2015

This work presents a new, very long snowfall time series collected in a remote site of Italian Apennine mountains (Montevergine Observatory, 1280 m a.s.l.). After a careful check, based on quality control tests and homogenization procedures, the available data (i.e. daily height of new snow) have been aggregated over winter season (December-January-February) to study the long-term variability in the period 1884–2020. The main evidences emerged from this analysis lie in (i) the strong interannual variability of winter snowfall amounts, in (ii) the absence of a relevant trend from late 19th century to mid-1970s, in (iii) the strong reduction of the snowfall amount and frequency of occurrence from mid-1970s to the end of 1990s (−45 and −17 % compared to the average recorded in 1884–1975 period, respectively), and in (iv) the increase of average snowfall amount and frequency of occurrence in the last 20 years. Moreover, this study shed light on the relationship between the snowfall variability observed in Montevergine and the large-scale atmospheric circulation. Six different synoptic types, describing the meteorological scenarios triggering the snow events in the study area, have been identified by means of a cluster analysis, using two essential atmospheric variables, the 500-hPa geopotential height and the sea level pressure (both retrieved from the third version of Twentieth Century Reanalysis dataset). Such patterns trace out scenarios characterized by the presence of a blocking high-pressure anomaly over Scandinavia or North Atlantic and by a cold air outbreak, involving both maritime and continental cold air masses. A further analysis demonstrates that the identified synoptic types are strongly related with different teleconnection patterns, i.e. the Arctic Oscillation (AO), the Eastern Atlantic Western Russia (EAWR), the Eastern Mediterranean Pattern (EMP), the North Atlantic Oscillation (NAO) and the Scandinavia pattern (SCAND), that govern the European winter atmospheric variability. The relevant decline in snowfall frequency and amounts between 1970s and 1990s can be mainly ascribed to the strong positive trend of AO and NAO indices, which determined, in turn, a decrease in the incidence of patterns associated to the advection, in central Mediterranean area, of moist and cold arctic maritime air masses. The recent increase in average snowfall amounts can be explained by the reverse trend of AO index and by the prevalence of neutral or negative EAWR pattern.

A Relaxed Eddy Accumulation (REA) LOPAP-System for Flux Measurements of Nitrous Acid (HONO)

In the present study a Relaxed Eddy Accumulation (REA) system for the quantification of vertical fluxes of nitrous acid (HONO) was developed and tested. The system is based on a three-channel-LOPAP instrument, for which two channels are used for the updrafts and downdrafts, respectively, and a third one for the correction of chemical interferences. The instrument is coupled to a REA gas inlet, for which an ultrasonic anemometer controls two fast magnetic valves to probe the two channels of the LOPAP instrument depending on the vertical wind direction. A software (PyREA) was developed, which controls the valves and measurement cycles, which regularly alternates between REA-, zero- and parallel ambient measurements. In addition, the assignment of the updrafts and downdrafts to the physical LOPAP channels is periodically alternated, to correct for differences in the interferences of the different air masses. During the study, only small differences of the interferences were identified for the updrafts and downdrafts excluding significant errors when using only one interference channel. In laboratory experiments, high precision of the two channels and the independence of the dilution corrected HONO concentrations on the length of the valve switching periods were demonstrated. A field campaign was performed in order to test the new REA-LOPAP system at the TROPOS monitoring station in Melpitz, Germany. HONO fluxes in the range of −4·1013 molecules m−2 s−1 (deposition) to +1.0·1014 molecules m−2 s−1 (emission) were obtained. A typical diurnal variation of the HONO fluxes was observed with low, partly negative fluxes during night-time and higher positive fluxes around noon. After an intensive rain period the positive HONO emissions during daytime were continuously increasing, which was explained by the drying of the upper most ground surfaces. Similar to other campaigns, the highest correlation of the HONO flux was observed with the product of the NO2 photolysis frequency and the NO2 concentration (J(NO2)·[NO2]), which implies a HONO formation by photosensitized conversion of NO2 on organic surfaces, like e.g. humic acids. Other postulated HONO formation mechanisms are also discussed, but are ranked being of minor importance for the present field campaign.

Impact of the COVID-19 pandemic related to lockdown measures on tropospheric NO₂ columns over Île-de-France

The evolution of NO2, considered as a proxy for air pollution, was analyzed to evaluate the impact of the first lockdown (17 March–10 May 2020) over the Île-de-France region (Paris and surroundings). Tropospheric NO2 columns measured by two UV-Visible Système d'Analyse par Observation Zénithale (SAOZ) spectrometers were analyzed to compare the evolution of NO2 between urban and suburban sites during the lockdown. The urban site is the observation platform QualAir (48∘50′ N / 2∘21′ E) at the Sorbonne University Pierre and Marie Curie Campus in the center of Paris. The suburban site is located at Guyancourt (48∘46′N / 2∘03′E), Versailles Saint-Quentin-en-Yvelines University, 24 km southwest of Paris. Tropospheric NO2 columns above Paris and Guyancourt have shown similar values during the whole lockdown period from March to May 2020. A decade of data sets were filtered to consider air masses at both sites with similar meteorological conditions. The median NO2 columns and the surface measurements of Airparif (Air Quality Observatory in Île de France) during the lockdown period in 2020 were compared to the extrapolated values estimated from a linear trend analysis for the 2011–2019 period at each station. Negative NO2 trends of −1.5 Pmolec. cm−2 yr−1 (∼ −6.3 % yr−1) are observed from the columns, and trends of −2.2 µg m−3 yr−1 (∼ −3.6 % yr−1) are observed from the surface concentration. The negative anomaly in tropospheric columns in 2020 attributed to the lockdown (and related emission reductions) was found to be 56 % at Paris and 46 % at Guyancourt, respectively. A similar anomaly was found in the data of surface concentrations, amounting to 53 % and 28 % at the urban and suburban sites, accordingly.

Formation conditions of an ice storm in Vladivostok in November 2020

Synoptic conditions for the formation of an unprecedented ice storm with the generation of long-lived high-intensity glaze ice on the vast territory in Primorsky Krai are investigated. The leading role of the strong extension of the layer with positive temperature towards the cold air mass and the existence of two-way temperature advection in the lower troposphere are shown. It is shown that the long-term preservation of glaze ice on the territory of the region was associated with the movement of the southern cyclone to the east and the arrival of cold air masses from the continent. Experiments were implemented to simulate freezing precipitation using the WRF-ARW mesoscale model. The simulation results made it possible to obtain more detailed data on the vertical structure of the atmosphere during the formation of freezing precipitation and to fill in the missing data for analysis. Keywords: severe weather events, ice accretion, glaze ice, freezing rain, ice pellets, numerical weather prediction, WRF-ARW

Analysis of air pollution in Primorsky Krai in 2019-2020 according to GMAO/NASA satellite monitoring

The results of modeling variations in atmospheric pollutants over Primorsky Krai in 2019 and 2020 based on GMAO/NASA satellite monitoring data are analyzed. It is shown that average annual concentrations of pollutants in 2020 decreased as compared to 2019: by 20–35% for sulfur dioxide; by 5–20% for sulfates; by 8–20% for carbon monoxide; by 25–40 % for particulate matter PM (1, 2.5, and 10 μm). One of the reasons for the air pollution decline in Primorsky Krai in 2020 is the reduction of anthropogenic load in the context of a decrease in industrial activity and traffic flows both in Primorye and in the adjacent areas of China. Episodes of high pollution in 2019 were formed under influence of the transboundary transport of polluted air masses. Keywords: air pollution, aerosol and chemical elements, transboundary transport, satellite monitoring, Primorsky Krai

Weather & weather systems at Schirmacher Oasis (Maitri) during recent two decades - A review

Indian Antarctic station Maitri experiences varying external influences from interior of east Antarctica as well as moving depressions and cyclones along the coast. The relative position of circumpolar trough and strengthening of high pressure centre near pole influences variation of atmospheric pressure at Maitri. The diurnal, daily and seasonal variation of temperature mainly depend upon moving pressure systems, katabatic winds, change of solar insulation with change of seasons, reflectivity from clouds and snow surface. The katabatic winds prevail over Maitri which is highly directional from South- East sector due to increase of slope towards south. The blizzards are main weather at Maitri, fog and white out are occasional phenomena. The precipitation is mostly in form of snowfall but rain is very rare at Maitri. Heavy or moderate snowfall indicative of active front leading edge of warm air masses being transported southwards. Strong temperature variant near Schirmacher oasis give precipitation in form of snow. Fog occurred due to slow movement of relatively warm air from lower latitude over the colder surface. Winter season witnessed more snowfall accumulation at Maitri than other season. During summer rise of temperature accompanied with absorption of latent heat by ice pellets in low level of atmosphere results precipitation in form of water droplets. Highest number of blizzards occurs during winter season whereas lowest number of blizzards occurs during summer season. Normally due to cyclonic activities, warm air masses transported towards the Schirmacher oasis which causes rise of temperature at Maitri. Longer duration of the blizzards over the station depends upon strength of slow moving blocking anticyclone situated east of Maitri at lower latitude. Tremendous fluctuation of atmospheric electric field observed before onset is a pre-indication of commencement of blizzards.