Synoptic weather systems are a major driver of spatial gradients in atmospheric CO2 mole fractions. During frontal passages, air masses from different regions meet at the frontal boundary creating significant gradients in CO2 mole fractions. We quantitatively describe the atmospheric transport of CO2 mole fractions during a mid‐latitude cold front passage and explore the impact of various sources of CO2. We focus here on a cold front passage over Lincoln, Nebraska on August 4th, 2016 observed by aircraft during the Atmospheric Carbon and Transport‐America campaign. A band of air with elevated CO2 was located along the frontal boundary. Observed and simulated differences in CO2 across the front were as high as 25 ppm. Numerical simulations using Weather Research and Forecasting Model with Chemistry at cloud resolving resolutions (3 km), coupled with CO2 surface fluxes and boundary conditions from CarbonTracker (CT‐NRTv2017x), were performed to explore atmospheric transport at the front. Model results demonstrate that the frontal CO2 difference in the upper troposphere can be explained largely by inflow from outside of North America. This difference is modified in the atmospheric boundary layer and lower troposphere by continental surface fluxes, dominated in this case by biogenic and fossil fuel fluxes. Horizontal and vertical advection are found to be responsible for the transport of CO2 mole fractions along the frontal boundary. We show that cold front passages lead to large CO2 transport events including a significant contribution from vertical advection, and that midcontinent frontal boundaries are formed from a complex mixture of CO2 sources.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Quantifying tropical cyclone cloud cover using Envisat retrievals -an example of a recent severe tropical cyclone,The eastern coast of peninsular India routinely receives the onslaught of devastating cyclonic storms. We suggest a novel method involving Envisat retrievals followed by application of the European Space Agency's (ESA's) Earth Observation Link Stand-Alone (EOLI-SA) catalogue for the calculation of cloud cover (CC) of tropical storms. In particular, we focus on the northeast monsoon, which is less studied as compared with the more regularly investigated southwest monsoon. We found that the CC was of the order of 946,598 km 2 on 23 November 2011. In contrast, we also calculated the CC of tropical cyclone Thane that occurred on 31 December 2011, which was found to be 1,222,224 km 2 -an increase of 197.5%. To further increase CC calculation accuracy, Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals were used simultaneously over both visible and shortwave infrared (SWIR) spectra. The precipitable water levels were analysed using Tool for High-resolution Observation Review (THOR) and Tropical Rainfall Measuring Mission (TRMM) retrievals. Envisat data were then used to track Thane's trajectory. These multiple-image analyses are coupled with large-eddy simulation runs -large velocities from sheared eddies were obtained at landfall. The runs were simultaneously performed over two locales on 29 December 2011 -first at Karaikal, where the impact of Thane was severe, and then at Chennai, where the cyclone's fury had become somewhat curtailed. This procedural analysis, coupled with model simulations, can be used effectively by Environmental Impact Assessment (EIA) personnel and decision-makers of the municipal corporations of vulnerable cities along coastal Tamil Nadu.

Increasingly the world over, climate modelers have suggested that local emissions may well affect cyclonic storms. The eastern coast of India, home to mega cities, is routinely battered by such storms over the period October-December. Additionally, these cities house millions of slum dwellers who cook their meals from unseasoned firewood yielding substantial amounts of biomass particles. These particles chemically age within a polluted air mass rendering them active as cloud condensation nuclei (CCN). This first study shows the genesis, progression and evolution of one such tropical disturbance, Hurricane Thane, which was modulated by these transient emissions, devastating the coast of Tamil Nadu on 30th December 2011.We show that auto-conversion rates converting cloud water to rain water are significantly altered by up to 12% when such emissions are included. Carefully designed numerical experiments using the Weather Research and Forecasting (WRF) model show an increase of 20.5% in the cloud water amounts when these effects are included. Emissions from Asian slums may well alter cyclonic activity elsewhere in South Asia. This study, using a state of the art numerical weather prediction model, indicates how local effects can be quickly obtained through offline modeling. In a nation of continental proportion where millions of under privileged persons live close to the most vulnerable coastal locations, quick alerting mechanisms by local institutions with limited resources (Government Colleges and Engineering Institutes) may well form a support system linking ordinary citizens with the local coast guard for purposes of mass evacuation well in advance.

The remit of mechanical engineering extends well beyond machines. Mechanical engineering theories have diverse applications the transport and distribution of particulate matter into a turbulent boundary layer involves a systematic application of fluid mechanics. In this paper, we have used fluid mechanical models accompanied by experimental observations to study how turbulent eddies transport and distribute cook stove emissions over slums in the megacity Chennai - the Detroit of India. It is home to 8 million people and is a manufacturing hub with a propensity to release a variety of suspended particulate matter mixed with marine aerosols transported from the Bay of Bengal. Of these 8 million, about 2 million live in slums-these impoverished slum dwellers comprise of Chennais huge unskilled work force. Our study revealed that they primarily use cow dung cakes and unseasoned wood to cook, releasing a huge amount of particulate matter up to radii of 10 microns (PM10). A scanning electron micro-graphy ascertained the drop size distribution ensuring that the majority of these particles were small enough for them to be easily transported by boundary layer eddies the latter are simulated using the United Kingdom Met Office Large Eddy Simulation Model. It is observed that the large eddies are spread over alternating up and down draughts with maximum vertical velocity perturbations of the order of 1 ms-1, which is significantly higher than the Stokesian still air settling rates of suspended particles. Whilst remaining aloft, they act as cloud condensation nuclei and thence grow into cloud droplets. The large cloud covers over Chennai city can be linked to this latter effect. Chennais hot and humid atmosphere ensures that these droplets collide within the cloud topped turbulent boundary layer to trigger a process of stochastic coalescence and subsequent rain showers.

No abstract

No abstract

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.