Integrating biomass, sulphate and sea-salt aerosol responses into a microphysical chemical parcel model: implications for climate studies

Quick Predictions of Onset Times and Rain Amounts from Monsoon Showers over Urban Built Environments

Predicting the onset times of precipitation over densely populated cities for the purposes of timely evacuation is a challenge. This paper explored a flooding event over an urban built environment in a South Asian mega city, Chennai, where extant urban planning models rely on predicted rainwater amounts for early warning and impact assessment studies. However, the time duration of flooding events is related to the nature of the urban sprawl in the built environment. Any evacuation measure is invariably tied down to the time duration over which the precipitation event occurs, and therefore to the expected time of a precipitation event to begin. In this context, a crucial parameter useful to municipal authorities is the onset time of precipitation. This study used optimised analytical formulations to predict this time, and the derived analytical expressions for the case study yielded comparable times estimated from a computer-intensive full-scale large eddy model within an accuracy of 2%. It is suggested that municipal authorities (who are non-experts in fluid mechanics) use this early prediction for the purposes of quick alerts to a congested city’s most vulnerable citizens within urban sprawls. However, for the procedure to work at its best, it involves a two-stage procedure. The first step involves the use of a parcel model to obtain the expected cloud droplet spectral spreads based on the prevailing dynamical characterisations. The second step involves an optimisation procedure involving cloud spectral properties from the first step to quantify both the auto-conversion rates and the threshold. Thereafter, an onset time calculation based on cloud properties is estimated. These new results are cast in closed form for easy incorporation into meteorological applications over a variety of urban scales. Rain mass amounts were also predicted analytically and used to configure Aeronautical Reconnaissance Coverage Geographic Information System (ARCGIS) to compute low drainage flow rates over the vulnerable parts of Chennai city. It was found that heavy precipitation over the North Chennai region yielded discharge rates to the tune of ~250 m3s−1 during a 24 h period, causing intense flooding in the low-lying areas around the Cooum River basin with a large population density, with estimates sufficiently corroborating observations.

How Atmospheric Large Eddies Transport Domestic Cook Stove Emissions over Slums: A Chennai City Case Study

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.