Journal of Atmospheric Science Research

Dense Fog in the Netherlands: Composition of the Nuclei that Contribute Most to the Droplet Number Concentration

2024-05-10T11:00:50+08:00

Dense fogs, with a visibility of less than 200 m, form a traffic hazard. Usually, models describing their formation use observations at the Cabauw super-site in the Netherlands for evaluation. A key parameter is the number of fog droplets and thus the number of aerosol particles on which the fog droplets form, the so-called fog nuclei (FN). No observational data are available for this key microphysical feature. An assumption is that this number scales with the concentration of the hygroscopic aerosol component sulfate. However, in the Netherlands nitrate and organics are the more important components of the total aerosol and thus possibly also of the FN. This short communication provides the first actual data via measurements with an aerosol mass spectrometer—AMS—for a period with dense fog events observed in November 2011. The aerosol in the relevant size range was composed of about half of the hygroscopic ammonium nitrate/sulfate. The other half consisted of organics; the low O/C ratio indicated that these compounds are rather hydrophobic; the hygroscopicity factor kappa of this mix was estimated at 0.3. This value implies that the activation diameter (the lowest diameter of the FN) was at least 150 nm. The mass distribution was converted into a number distribution which showed a sharp decrease as a function of size for diameters above this threshold. This result implies that the vast majority of the FN have diameters to the activation diameter. These smallest FN contained ammonium nitrate as the major hygroscopic compound. Currently, data for other dense fogs are evaluated to search for a possible generality of this finding.

Convective Phenomenes in the Context of Meso-β-scale Convective Structures

2024-03-13T16:45:01+08:00

This review article presents the results of radar studies of convective phenomena in Moldavia and the North Caucasus using Eulerian (ECS) and Lagrangian (LCS) coordinate systems. Application of the Lagrangian approach allowed us to exclude the influence of the tropospheric displacement and to obtain integral grid patterns of thunderstorm-hail processes. These structures are especially well manifested at small wind shears (up to 1 m/sec/km). At large shears, the mesh structures are transformed predominantly into linear structures. The methodology for obtaining integral pictures of radio echoes of thunderstorm processes is described. Intersections of linear elements, which we call facets, occur at nodes. The latter plays a particularly important role in the dynamics and kinematics of convective storms. The development of storms occurs along the facets and at the nodes of meso-β-scale convective structures (MMCS), which explains the mechanisms of splitting and merging of storms: in the first case the facets diverge, in the second case they converge. The relations of motion vectors for different types of storms are obtained. It is shown that the direction of the radio echo canopy coincides with the storm motion trajectory; the evolution vector (propagation) for the most powerful storms deviates from the storm displacement direction by 80°–135°. The structure of the updated band within which the Flanking Line is formed for supercells and multicells is studied. Mnemonic rules have been derived that allow one to infer from instantaneous patterns of anvil orientation and the mutual location of storms whether they are converging or diverging, and to identify left- or right-moving storms. A hypothesis on the internal structure of the cold front of the 2nd kind is stated. The main conclusion of the work is that the evolution of storms is determined by the configuration of meso-β-scale convective structures. This explains various convective phenomena from unified positions. The results are applicable in works on modification of convective cloudiness, for ultra-short-term forecasts of dangerous phenomena, storm warnings of the population, rescue services, etc.

Estimating Chemical Concentrations of Dust PM2.5 in Iraq: A Climatic Perspective Using Polynomial Model and Remote Sensing Technology

2024-06-24T16:01:44+08:00

Air pollution and climate change are interrelated issues, with air pollution levels in Iraq currently exceeding World Health Organization standards. This study aimed to evaluate air quality in Iraq by utilizing climatic data, such as temperature, humidity, and gaseous pollutants for assessing the health effects based on processed and estimated data. The research was conducted between August and November 2020, using remotely sensed images and geographical information techniques. Two methods; Geographic Information Systems GIS-based multiple regression and a polynomial model, were employed to estimate PM_2.5 levels in the study area. The results showed a significant influence of climatic variables on air pollution in Iraq, with varying effects on PM_2.5 estimation. The health impact ranged from good to unhealthy, with most provinces experiencing poor air quality. Southern parts of Iraq exhibited PM_2.5 levels surpassing the healthy threshold. The predictive linear and polynomial model's accuracy was assessed through regression, yielding high correlation coefficients (R² ) of 0.89, 0.95, 0.98, and 0.96 for August to November, respectively. While model validation accuracy ranged between 85–94 %. The study emphasizes the vital role of climate data in understanding the dispersion of air pollutants and their significant impacts on the environment. Addressing air pollution and climate change, as per the SGS-13 "Climate Action", are interconnected and require comprehensive strategies for mitigation.

Evaporation and Fragmentation of the Electrified Droplets in the Polar Clouds during Spring Season as a Key Mechanism of the Ozone Depression Formation

2024-05-14T08:54:26+08:00

This study focuses on the role of the charged particles in the formation of the springtime ozone depression in the polar atmosphere. Analysis of experimental data collected in the polar atmosphere indicates that the small charged particles, predominantly ion clusters, can play a key role in the ozone molecules destruction and springtime ozone depression. The formation of these particles increases strongly during the spring season in the process of evaporation and fragmentation of the cloud-charged droplets in the lower stratosphere and upper troposphere. Additionally, small charged particles can also affect the formation and accumulation of chlorine monoxide under cold conditions of the lower stratosphere. At the same time, the chlorine mechanism of ozone destruction cannot completely explain the ozone depression formation, which probably takes place not only inside the polar vortex in the lower stratosphere but outside it also, both at the altitudes of the lower stratosphere and upper troposphere. The assumption that the charged particles play an important role in the process of ozone depression formation was put forward by previous studies, but in this research work, this assumption has been additionally confirmed, which is the springtime growth of ion clusters concentration as a result of the droplet's evaporation and defragmentation in the polar atmosphere is a key mechanism of the ozone depression formation. We simulated the process of evaporation and fragmentation in the case of a 10-micron size droplet, which implies the possible catalytic cycles of ozone destruction with the ion clusters. For the first time, the role of the Earth's magnetic field and the Polar vortex wind in the unipolar charge accumulation on the cloud particles in the lower stratosphere and upper troposphere not only inside the Polar vortex but also outside of it was substantiated. This fact in our point of view can give rise to the large-scale springtime ozone depression, spreading over the midlatitudes, which size is vastly greater than it is commonly supposed.