Origin and Route of Severe Dust Storms in West Asia (with Horizontal Visibility Less Than 1000 Meters)

Storms are intensified atmospheric phenomena which are sometimes accompanied by heavy rainfall and sometimes by dust. Dust storms, especially storms with horizontal visibility of fewer than 1000 meters, have always been harmful and detrimental to human comfort and health. In recent decades, the worrisome phenomena of conflict, climate change, and droughts have increased the frequency of dust storms in West Asia. Identifying the source and route of dust storms is the first step in limiting the harm they inflict. To investigate this phenomenon, using the daily data of the Meteorological Organization of Iran, storms with horizontal visibility of less than 1000 meters in the southwestern region of Iran, as one of the destination areas of these storms, in a statistical period of 33 years (1987 to 2019) was extracted. First, the monthly, seasonal and annual distribution of dust storms in 13 synoptic stations in this area was investigated. Then, using the site https://www.ready.noaa.gov/HYSPLIT by backward method from the GDAS data system with a step of 0.5 degrees, the origin and path of the storms were identified. Finally, maps of each route were drawn in ArcGIS 10.6. The findings of this study revealed that the biggest number of dust storms occurred in the winter, in terms of temporal distribution (38% of storms). With 23% of storms, spring is in second position. In terms of monthly distribution, the month of January has the most storms, followed by February and December. Storms decrease in intensity as they move from the south to the north, and from the west to the east of the region. The central region of Iraq ranks first in terms of storm origin, accounting for 25% of all storms. If dust storms originating in western Iraq are added to this number, about 35% of storms in west Asia originate in western and central Iraq. Regarding the pattern of large-scale atmospheric circulation prevailing in the middle layer of the atmosphere in this region, most of these dust storms in the west-east direction, after passing through the center and south of Iraq, enter Iran. The study also shows that storms in Syria، Jordan or northwestern Saudi Arabia, are very thick. These storms cover the middle layer of the troposphere and then affect high stations such as Shahrekord and Yasuj with an altitude of more than 2000 meters.

Horizontal Visibility in Forests

The important variable of horizontal visibility within forest stands is gaining increasing attention in studies and applications involving terrestrial laser scanning (TLS), photographic measurements of forest structure, and autonomous mobility. We investigated distributions of visibility distance, open arc length, and shaded arc length in three mature forest stands. Our analysis was based (1) on tree position maps and TLS data collected in 2013 and 2019 with three different scanners, and (2) on simulated digital twins of the forest stands, constructed with two pattern-generation models incorporating commonly used indices of tree position clumping. The model simulations were found to yield values for visibility almost identical to those calculated from the corresponding tree location maps. The TLS measurements, however, were found to diverge notably from the simulations. Overall, the probability of free line of sight was found to decrease exponentially with distance to target, and the probabilities of open arc length and shaded arc length were found to decrease and increase, respectively, with distance from the observer. The TLS measurements, which are sensitive to forest understory vegetation, were found to indicate increased visibility after vegetation removal. Our chosen visibility prediction models support practical forest management, being based on common forest inventory parameters and on widely used forest structure indices.

Estimation of Atmospheric Turbidity Parameters in Ile-Ife, Nigeria

This study estimated the levels of atmospheric turbidity in Ile-Ife, a tropical location in the Southwest of Nigeria, from November, 2017 to March, 2019. This was with the aim to quantify the degree of atmospheric cleanliness of the study location. The methods of estimation used are: the Angstrom turbidity parameters (α and β), Linke turbidity factor (TL) and horizontal visibility (VH). The values of α and β range between 0.6 and 1.4; 0.10 and 0.91 respectively. The values obtained for TL varied between 1 and 7 while visibility values ranged between 2 and 14 km. Maximum values of β and TL (corresponding to low values of VH) were obtained in the dry season (particularly in the months of January and February) while the lowest values of the same methods of estimation (corresponding to high values of VH) were recorded in the wet season (specifically in August and September). The elevated turbidity observed in the dry season was linked to episodes of Harmattan dust storms usually experienced at the study location. The study concluded that a polluted atmosphere dominates the study location especially in the dry season as indicated by the different atmospheric turbidity parameters.

Dampak pembatasan sosial berskala besar terhadap kualitas udara di Jakarta

Abstrak Beberapa negara di dunia memberlakukan pembatasan sosial dan karantina wilayah sebagai upaya untuk menekan laju penularan wabah virus COVID-19. Pembatasan sosial dan karantina wilayah memberikan dampak negatif bagi perekonomian, namun juga dapat berdampak positif bagi perbaikan kondisi lingkungan khususnya kualitas udara di suatu wilayah. Selama periode Pembatasan Sosial Berskala Besar (PSBB) di Jakarta tahun 2020, aktivitas penduduk di luar rumah menurun secara signifikan. Penelitian ini bertujuan untuk menganalisis secara kuantitatif perubahan parameter kualitas udara berupa PM2.5 dan visibility di Jakarta selama periode sebelum (2019) dan setelah pandemi (2020) menggunakan metode statistik. Pengaruh mobilitas penduduk dan distribusi spasial konsentrasi polutan juga dianalisis dalam penelitian ini. Hasil penelitian menunjukkan selama masa pandemi COVID-19, terdapat pengurangan konsentrasi polutan pada tahun 2020 hingga lebih dari 100 persen dibandingkan tahun 2019. Jarak pandang mendatar di Jakarta juga meningkat hingga 11 persen selama PSBB. Mobilitas penduduk mempengaruhi konsentrasi polutan di Jakarta sebesar 30 persen dan distribusi spasial menunjukkan adanya fluktuasi konsentrasi PM2.5 sebelum dan setelah diberlakukannya PSBB. Abstract Countries worldwide have implemented some sort of lockdowns to slow down COVID-19 infection and mitigate it. Lockdown due to COVID-19 has drastic effects on social and economic fronts. However, this lockdown also has some positive effects on the natural environment, especially on air quality. During the 2020 PSBB period in Jakarta, outdoor activity decreased significantly. This study quantitatively analyzes air quality parameters of PM2.5 and visibility changes in Jakarta during the period before (2019) and after the pandemic (2020) using statistical methods. The impact of mobility to polution also become a concern in this study. The results confirmed an improvement in air quality due to the implementation of social restrictions during the COVID-19 pandemic. PSBB has an impact on reducing pollutant concentrations by more than 100 percent during PSBB compared to 2019. The horizontal visibility in Jakarta also increased by 11 percent during the PSBB. Mobility has affected PM2.5 concentration by 30 percent in Jakarta, and spatial distribution of PM2.5 shows evidence of fluctuation during and before PSBB enacted.

A new conceptual model for adiabatic fog

Visibility reduction caused by fog can be hazardous for human activities, especially for the transport sector. Previous studies show that this problem could be mitigated by improving nowcasting of fog dissipation. To address this issue, we propose a new paradigm which could potentially improve our understanding of the life cycle of adiabatic continental fogs and of the conditions that must take place for fog dissipation. For this purpose, adiabatic fog is defined as a layer filled with suspended liquid water droplets, extending from an upper boundary all the way down to the surface, with a saturated adiabatic temperature profile. In this layer, the liquid water path (LWP) must exceed a critical value: the critical liquid water path (CLWP). When the LWP is less than the CLWP, the amount of fog liquid water is not sufficient to extend all the way down to the surface, leading to a surface horizontal visibility greater than 1 km. Conversely, when the LWP exceeds the CLWP, the amount of cloud water is enough to reach the surface, inducing a horizontal visibility of less than 1 km. The excess water with respect to the critical value is defined as the reservoir liquid water path (RLWP). The new fog paradigm is formulated as a conceptual model that relates the liquid water path of adiabatic fog with its thickness and surface liquid water content and allows the critical and reservoir liquid water paths to be computed. Both variables can be tracked in real time using vertical profiling measurements, enabling a real-time diagnostic of fog status. The conceptual model is tested using data from 7 years of measurements performed at the SIRTA observatory, combining cloud radar, microwave radiometer, ceilometer, scatterometer, and weather station measurements. In this time period we found 80 fog events with reliable measurements, with 56 of these lasting more than 3 h. The paper presents the conceptual model and its capability to derive the LWP from the fog top height and surface horizontal visibility with an uncertainty of 10.5 g m−2. The impact of fog liquid water path and fog top height variations on fog life cycle (formation to dissipation) is presented based on four case studies and statistics derived from 56 fog events. Our results, based on measurements and an empirical parametrization for the adiabaticity, validate the applicability of the model. The calculated reservoir liquid water path is consistently positive during the mature phase of fog and starts to decrease quasi-monotonously about 1 h before dissipation, reaching a near-zero value at the time of dissipation. Hence, the reservoir liquid water path and its time derivative could be used as indicators of the life cycle stage, to support nowcasting of fog dissipation.