Journal of Atmospheric Science Research

Assessing Subseasonal Forecasts of Dry Spells and Heatwaves at the Regional Scale in Brazil

Christopher Cunningham — 2024-10-15

This study evaluates the performance of subseasonal forecasts for dry spells and heatwaves at a regional scale in Brazil. The forecasts’ verification was designed to provide end-users with relevant information about the forecasts’ quality. The U.K. Met Office model was assessed using a significant sample of weekly forecasts: 552 for dry spells and 240 for heatwaves. The analysis reveals that the overall performance of the forecasts is low, with a chance of detecting an event close to 0.2, indicating that only one out of five observed dry spells is accurately predicted on average. The application of quantile mapping corrections demonstrates improvements in predicting shorter dry spells (up to 5 days) and longer lead times, although the timing of these forecasts often remains inaccurate, leading to increased false alarms. A significant improvement in the forecast quality occurs when categorization by duration is disregarded. The detection chances increase to 0.5−0.7 for dry spells and 0.5 for heatwaves. The Brier Score indicates that the probabilistic forecasts issued by the model are equivalent or less skilful than climatological probabilities. Overall, the findings underscore the challenges in forecasting dry spells and heatwaves in Brazil and highlight the need for ongoing improvements in forecasting methodologies to enhance their reliability and utility for regional decision-making. This research contributes to understanding subseasonal climate forecasting and its implications for managing climate-related risks in Brazil.

A Formation of Atmospheric Aerosol Particles Due to Gas-to-Particle Conversion in Dark Conditions and the Particles’ Evolution in Large (3200 m3) Isolated Volume

Sergey Dubtsov — 2024-10-11

absence. The study was carried out in the Large Aerosol Chamber (LAC) of Research and Production Association (RPA) "Typhoon" having 3200 m³ volume. Because of the large size of the LAC, it is possible to exclude the boundary conditions influence by chamber walls and the equipment inside the LAC on the processes under study. The LAC has two (external and internal) High Efficiency Particulate Air (HEPA) 13 class filters installed at the entrance and inside it. First, we fill out the LAC of the atmospheric air and close it. After that, we purify the air inside the LAC by the internal filter. The number concentration of particle sizes above 15 nm decreases down to 50 particles per cm³. However, after a while, we observe increasing the particle number concentration by more than two orders of magnitude. We suppose that new formed particles due to gas-to-particle conversion were detected. We again purify the air inside the LAC by the internal filter. The particle number concentration decreased down to 10-20 particles per cm³ and remained at this low value for more than 300 hours. Our experiments indicate the necessity to use the two-stage procedure for cleaning working areas, with a time gap enabling gaseous precursors to form new particles, removable by HEPA 13 filter. Regularities of the growth of the newly formed particles from 15 nm size to cloud condensation nuclei characteristic size under controlled conditions were investigated. The observed regularities could contribute to understanding the atmospheric aerosol formation process responsible for cloudiness and precipitations.

Study on Cloud Characteristics in Western Liaoning, China Based on Millimeter-Wave Cloud Radar

Nan Shan — 2024-10-15

Based on the millimeter-wave cloud radar detection data from the western region of Liaoning Province, China (hereinafter referred to as western Liaoning) in 2020, the vertical structure characteristics of clouds were studied. The analysis results show that: (1) The occurrence frequency of clouds is 25.50%, while single-layer clouds occurrence frequency is 19.45% accounted for the largest proportion. The diurnal variation of occurrence rates differs across seasons. High clouds have the highest occurrence frequency, accounting for 40.03% of all clouds. (2) The average rainfall intensity of cloud precipitation throughout the year is 3.1 mm/h, and the precipitation mainly originates from single-layer and double-layer clouds. The rainfall intensity weakens as the number of cloud layers increases, and the precipitation of multi-layer clouds is mainly produced by low-layer clouds. (3) The average thickness of the cloud interlayer for precipitating clouds is 1.4 km, with 82.1% of cloud interlayer thicknesses being less than 2 km. The average thickness of the cloud interlayer for non-precipitating clouds is 1.84 km, with 70.8% of cloud interlayer thicknesses being less than 2 km. The cloud interlayer thickness generally decreases with the increase in the number of cloud layers.

Spatial Changes of Driving Parameters Affecting Cyclonic Activity over the North Indian Ocean from 1960 to 2020

Akshay Kumar Sagar — 2024-10-15

This study undertakes a thorough analysis of the elements that influence the variability of tropical cyclones (TC) in the North Indian Ocean (NIO) from 1960 to 2020, with a specific focus on the periods before and after the monsoon season. The study utilizes historical satellite data to investigate the factors that impact the formation, strength, and trajectories of cyclones. The primary method for evaluating cyclone strength is by calculating the Accumulated Cyclone Energy (ACE). The study observes a decreasing trend in ACE levels during 1991–2005, which started increasing just after from 2006 to 2020. The Bay of Bengal (BoB) has a more uniform distribution of ACE in comparison to the Arabian Sea (AS), with higher average values and more variability over the Main Development Region (MDR), which is the area where cyclone development occurs most frequently. Cyclones of greater intensity generally occur following the monsoon season. Examination of storm paths reveals that cyclones with greater intensity frequently hit the northeastern and southeastern coastal regions of India. The study emphasizes notable discrepancies in parameters within the MDR, which impact cyclone strength and ACE values throughout various periods.