Dipjyoti Mudiar

The extratropical Andes, a hotspot for landfalling atmospheric rivers (ARs), are prone to extreme precipitation and related hydrological hazards, including floods and landslides. An improved understanding of the drivers of precipitation intensification during AR landfall is critical for hazard preparedness. Focusing on 50 zonally elongated ARs (ZARs), we demonstrate that precipitation amplification over the Andes is largely associated with strong ascent produced by orographic lifting of ZAR flow and further strengthened by the release of atmospheric instabilities. The efficient realization of these instabilities is linked to large surface relative humidity, , particularly over regions with steep elevation gradients. We further demonstrate that ZAR‐related moisture convergence and terrain‐modulated heat advection in these regions lead to an increase in over the steep Andean terrain. This study emphasizes that accurately estimating precipitation intensification and its spatial distribution during ZAR landfall requires an improved understanding of both moisture and heat transport to the extratropical Andes.

The extratropical Andes, a hotspot for landfalling atmospheric rivers (ARs), are prone to associated extreme precipitation and related hydrological hazards, including floods and landslides. An improved understanding of the drivers of precipitation intensification during AR landfall is critical for hazard preparedness. Focusing on 50 zonally elongated ARs (ZARs), we demonstrate that precipitation amplification over the Andes is largely driven by strong updrafts produced by orographic lifting of ZAR flow and further strengthened by atmospheric instabilities. These instabilities are amplified by large surface relative humidity, particularly over regions with steep elevation gradients. We further demonstrate that ZAR-related moisture convergence and terrain-modulated heat advection in these regions lead to an increase in surface relative humidity over the steep Andean terrain. This study emphasizes that accurately estimating precipitation intensification and its spatial distribution during ZAR landfall requires an improved understanding of both moisture and heat transport to the extratropical Andes.

Atmospheric rivers (ARs) are known to produce both beneficial and extreme rainfall, leading to natural hazards in Chile. Motivated to understand moisture transport during AR events, this study performs a moisture budget analysis along 50 zonally elongated ARs reaching the western coast of South America. We identify the convergence of moist air masses of tropical/subtropical origin along the AR as the primary source of vertically integrated water vapor (IWV). Over the open ocean, moisture convergence is nearly balanced by precipitation. The advection of moisture along the AR, although smaller compared to mass convergence, significantly increases toward the landfalling region. The near conservation of IWV over the open ocean, observed by tracking a Lagrangian atmospheric column along the ARs, is the explanation behind the seemingly tropical origin of ARs in time‐lapse visualizations of IWV.

Atmospheric rivers (ARs) are known to produce both beneficial and extreme rainfall, leading to natural hazards in Chile. Motivated to understand moisture transport during AR events, this study performs a moisture budget analysis along 50 zonally elongated ARs reaching the western coast of South America. We identify the convergence of moist air masses of tropical/subtropical origin along the AR as the primary source of vertically integrated water vapor (IWV). Over the open ocean, moisture convergence is nearly balanced by precipitation. The advection of moisture along the AR, although smaller compared to mass convergence, significantly increases toward the landfalling region. The near conservation of IWV over the open ocean, observed by tracking a Lagrangian atmospheric column along the ARs, is the explanation behind the seemingly tropical origin of ARs in time-lapse visualizations of IWV

Atmospheric rivers (AR) are transient, narrow, and elongated channels in the atmosphere through which poleward transport of water vapor takes place from the tropics. In central-southern Chile, ARs contribute about 50% of the annual precipitation. ARs also produce extreme rainfall events, which may occasionally result in compound events. The water vapor associated with an AR originates from evaporation from the ocean, local mass convergence, and direct poleward moisture transport from the tropics. One way to understand the sources of moisture along an AR is the analysis of column integrated water vapor (IWV) budget, as suggested in previous studies. In this study, we have evaluated moisture and heat budgets for 50 land-falling zonal AR between 1980 and 2023 that caused heavy to extreme rainfall in the Southern Andes. The ARs are identified based on a global AR detection algorithm included in the ARTMIP (Guan and Waliser, 2018). The budget terms for all the ARs are calculated using the ERA5 reanalysis datasets along a backward trajectory obtained from the HYSPLIT trajectory model at 6-hour intervals. The budget analysis suggests that while mass convergence dominates the vertically integrated water vapor transport (IVT), the advection of moisture is significantly enhanced near the coast and the landfalling region. It is shown that the enhanced IWV bands from the tropics and subtropics can merge along the AR channel to enhance moisture convergence. The convergence of the tropical IWV bands occurs in a region between a stationary subtropical anticyclone and a midlatitude trough which migrate towards the continent. This region of convergence further acts as a source of moisture and heat that ends up being transported to the subtropical Andes. Over the land-falling regions, the IVT convergence and precipitation rate remain tightly associated (R2 =0.79), suggesting stronger IVT convergence (intense AR) may produce heavy rainfall events in Chile. It is also shown that synergistic action between moisture and heat enhances IVT convergence along an AR. An enhanced IVT convergence along AR channels produces intense AR. These intense AR can produce extreme rainfall events when they encounter coastal mountains and the Andes through the orographic precipitation enhancement mechanisms.

Four years of Indian Institute of Tropical Meteorology lightning location network lightning observation data are used to determine the seasonal and spatial (over different geographical locations) distribution of the ratio of intra‐cloud (IC) lightning to cloud‐to‐ground (CG) lightning in thunderstorms over the Indian subcontinent. The ratio is high (6–10) in the northwestern parts and low (0.5–3.5) in the northeastern parts. No prominent latitudinal variation of the IC to CG ratio exists, but a climatological seasonal variability exists over all regions. In the pre‐monsoon season (March–May), the mean ratio is observed to be 3.81 with a standard deviation of 0.79, and during the monsoon season (June–September), a value of 3.04 with a standard deviation of 0.50. Although convective available potential energy is the regulating factor, little dependency has been found between the ratio of IC to CG lightning (IC:CG ratio) and the total flash rate (f), as well as with cold cloud depths. The ratio is observed to be proportional to the total flash rate as f^0.61. The cold cloud depth is most prominently linked with the regional and seasonal IC:CG ratio. The implication of these observed results has the importance of separating CG lightning flash from total and can be used in numerical models to give a proper prediction of CG lightning in hazard mitigation.

The recent emergence of compelling evidence (Mudiar et al., 2018, 2021a 2021b) regarding a significant impact of cloud electrification on rain microphysical processes raises curiosity on the potential dynamical implications of cloud electrification. In this study, the consequence of cloud electrification has been explored from a perspective of interaction between cloud microphysics and dynamics using observational data and numerical models in a tropical condition. It is shown that the strongly electrified (SE) clouds exhibit a reduced value of rain intercept parameter, N0 relative to the weakly electrified (WE) counterpart facilitated by the in-cloud electric field. This process results in a reduction in rain evaporation rate in the warm phase of the cloud, thereby enhancing the surface rain intensity. From a dynamical perspective, the reduced rain evaporation rate gives positive feedback to storm energetics by reducing latent cooling. The reduced latent cooling delays the downdraft thereby facilitating an invigoration of convection. This electrically induced invigoration is termed ‘Dynamical Invigoration of Electrified Storms’.

Simultaneous measurements of cloud electric field and raindrop size at the Earth's surface have been analyzed to investigate an anticipated relation between the two cloud parameters. A significant positive correlation is observed between the magnitude of the surface electric field and raindrop size supported by a theoretical framework advanced here. It is shown that in the presence of an electric field, raindrops increase their size through electrically induced collision and coalescence processes near the Earth's surface. This study also demonstrates that the presence of an electric field inside the cloud can enhance the rain intensity by influencing the growth rate of raindrops. This new insight may be useful for a proper understanding of the rain microphysics and for developing better numerical weather models for simulation and forecasting of heavy rainfall events associated with stronger in‐cloud electrical environments.

Simultaneous measurements of cloud electric field and raindrop size at the surface have been analysed to investigate an anticipated relation between the two cloud parameters. A significant positive correlation is observed between the magnitude of the surface electric field and raindrop size supported by a theoretical framework advanced here. It is shown that in the presence of an electric field, raindrops increase their sizes through electrically-induced collision and coalescence processes near the Earth's surface. This study also demonstrates that the presence of an electric field inside the cloud can enhance the rain intensity by influencing the growth rate of raindrops. This new insight may be useful for a proper understanding of the rain microphysics and for developing better numerical weather models for simulation and forecasting of heavy rainfall events associated with stronger in-cloud electrical environments.