[1] Intense gravity wave activities were investigated in the lower stratosphere during the typhoon 9426. Strong vertical winds were observed just a few hours before the arrival of the typhoon-center at the MU radar site. About 30 min to 1 hour after the typhooncenter had passed, a considerable reduction in vertical wind amplitude was detected. Dominant gravity waves showed time period in the range of 7-8 min, 15 min, and 40-60 min in the upper troposphere and lower stratosphere. In the vicinity of the central region of the typhoon, a gravity wave was observed, which was monochromatic in nature with a vertical wavelength $3 km between 1.5 km and 23 km height. In the lower stratosphere, the horizontal wavelength for the prominent period was detected in the range of 10-15 km (for 15 min wave period) and 25-50 km (for 40-60 min wave period). The vertical wavelength of these waves was examined from 2.5 km to 4.0 km. In the horizontal direction, the intrinsic group velocity was estimated between 9 ± 2 and 11 ± 2 m/s. Near the tropopause, the average direction of group velocity was assessed at about 20°± 3°f rom the horizontal. The generation of gravity wave like features, in the lower stratosphere, is believed induced by convection, as the low temperature of the clouds indicates a deep penetration over the radar region as seen in the satellite GMS images.
Delhi, a tropical indian megacity, experiences one of the most severe air pollution in the world, linked with diverse anthropogenic and biomass burning emissions. First phase of COVID-19 lockdown in India, implemented during 25 March to 14 April 2020 resulted in a dramatic near-zeroing of various activities (e.g. traffic, industries, constructions), except the "essential services". Here, we analysed variations in the fine particulate matter (PM 2.5) over the Delhi-National Capital Region. Measurements revealed large reductions (by 40-70%) in PM 2.5 during the first week of lockdown (25-31 March 2020) as compared to the pre-lockdown conditions. However, O 3 pollution remained high during the lockdown due to non-linear chemistry and dynamics under low aerosol loading. Notably, events of enhanced pM 2.5 levels (300-400 µg m −3) were observed during night and early morning hours in the first week of April after air temperatures fell close to the dew-point (~ 15-17 °C). A haze formation mechanism is suggested through uplifting of fine particles, which is reinforced by condensation of moisture following the sunrise. The study highlights a highly complex interplay between the baseline pollution and meteorology leading to counter intuitive enhancements in pollution, besides an overall improvement in air quality during the COVID-19 lockdown in this part of the world. The pandemic due to spread of novel Corona virus, commonly known as the COVID-19, has led to partial or complete lockdown in several countries around the world. The spread of deadly virus has caused deaths estimated to more than two hundred thousand people over a period of December 2019-April 2020. However, air pollutants and COVID-19 are linked to have played a major role in huge number of deaths 1,2. In order to contain its impact in India, the first phase of complete lockdown imposed from 25 March to 14 April 2020, which was further extended till 03 May 2020. As a result, the transport, construction works, industries and other commercial activities, which could have injected pollutants or produce dust, are stopped and remained at its minimal level. Unprecedented reductions in anthropogenic activities yielded to very low values of emissions resulting in significantly improved air quality over the Delhi-National Capital Region (NCR) [up to 50% reduction in fine particle
[1] A numerical experiment is conducted using an Atmospheric General Circulation Model (AGCM) to investigate the presence of the large potential energy over a region of low topography and little convective activity, focusing on the tropical Atlantic region (10°E to 20°W, 0°t o 20°S). It is found that gravity waves with a time period of 24 hours are excited near the Equator ($5°-15°N) in a region of large moist heating extending vertically up to 10-13 km. The gravity waves propagate upward from this region with a bias toward the south and are manifested as large energy fluxes in the cross equatorial region. Enhanced energy fluxes are therefore simulated at 20-30 km altitude over a region with no significant source of gravity waves, and are confirmed using Global Positioning Satellite/ Meteorology (GPS/MET) experiment data.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.