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This study presents a detailed analysis of the 2019 record-breaking seasonal (June-September) monsoon rainfall, since 1901, over large areas of Western India, which evolved in the backdrop of an intense positive Indian Ocean Dipole (p-IOD) event. Analysis of multi-source observational datasets (rain gauge, GPM, NOAA, ERA5) reveals that the 2019 unusually excessive and flood-producing monsoonal rains over Western India markedly came from three intense rain episodes (IREs) viz., 1) 28th June - 12th July 2) 24th July -11th August 3) 2nd September – 13th September and was characterised by large-scale bands of organised convection. We observe a preponderance of stratiform precipitating mesoscale convective systems embedded within the organised rainband. Regression analyses of various atmospheric fields were performed to understand the dominant spatial structures during the IRE days. Our findings indicate that the continual top-heavy stratiform heating forced a Rossby-wave pattern with regional stretching of mid-tropospheric potential vorticity across South and Southeast Asia. Results show that the pIOD-induced enhanced cross-equatorial moisture transport fostered deep convection and heavy precipitation in this region. This study highlights the potential ramifications of intense pIOD manifestations on IREs and their hydrological consequences over the monsoon-centric areas of South and Southeast Asia in the 21st century., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Earth System Models (ESM) are important tools that allow us to understand and quantify the physical, chemical & biological mechanisms governing the rates of change of elements of the Earth System, comprising of the atmosphere, ocean, land, cryosphere and biosphere (terrestrial and marine) and related components. ESMs are essentially coupled numerical models which incorporate processes within and across the different Earth system components and are expressed as set of mathematical equations. ESMs are useful for enhancing our fundamental understanding of the climate system, its multi-scale variability, global and regional climatic phenomena and making projections of future climate change. In this chapter, we briefly describe the salient aspects of the Indian Institute of Tropical Meteorology ESM (IITM ESM), that has been developed recently at the IITM, Pune, India, for investigating long-term climate variability and change with focus on the South Asian monsoon.

This popular article provides a short summary of the progress and prospects in Weather and Climate Modelling for the benefit of high school and undergraduate college students and early career researchers. Although this is not a comprehensive scientific article, the basic information provided here is intended to introduce students and researchers to the topic of Weather and Climate Modelling - which comes under the broad discipline of Atmospheric / Oceanic / Climate / Earth Sciences. This article briefly summarizes the historical developments, progress, scientific challenges in weather and climate modelling and career opportunities.

The article of record as published may be located at http://dx.doi.org/10.1175/WAF1029.1 A numerical study using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) was performed to assess the impact of initial and boundary conditions, the parameterization of turbulence transfer and its coupling with cloud-driven radiation, and cloud microphysical processes on the accuracy of mesoscale predictions and forecasts of the cloud-capped marine boundary layer. Aircraft, buoy, and satellite data and the large eddy simulation (LES) results during the Dynamics and Chemistry of Marine Stratocumulus field experiment (DYCOMS II) in July 2001 were used in the assessment. Three of the tested input fields (Eta, NCEP, and ECMWF) show deficiencies, mainly in the thermodynamic structure of the lowest 1500 m of the marine atmosphere. On a positive note, the simulated marine-layer depth showed good agreement with aircraft observations using the Eta fields, while using the NCEP and ECMWF datasets underestimated the marine-layer depth by about 20%–30%. The predicted turbulence kinetic energy (inversion strength) was about 50% of that obtained from the LES results (aircraft observed). As a consequence of moisture overprediction, the predicted liquid water path was twice the observed by 1–2 g kg 1. The sensitivity tests have shown that the selections of turbulence and cloud microphysical schemes significantly influence the turbulence estimates and cloud parameters. Two of the tested turbulence schemes (Eta PBL and Burk–Thompson) did not exhibit the coupling with radiation. The significant differences in the simulated turbulence estimates appear to be a consequence of the use of water-conserving potential temperature variables. The microphysical parameterization, which uses the number concentration of cloud drops in the autoconversion process, simulates a realistic evolution of precipitable hydrometeors in the cloudy marine layer on the positive side, but on the other hand enhances the decoupling in the turbulence structure. This study can provide guidance to operational forecasters concerning accuracy issues of the commonly used large-scale analyses for model initialization, and optimal selection of model parameterizations in order to simulate and forecast the cloudy atmospheric boundary layer over the ocean.

Satellite-tracked drifter data and meteorological wind measurements indicated summer bora event of 22 - 25 June 1995 as interesting from both meteorological and oceanographic point of view. The studied summer situation was controlled by a mesoscale atmospheric disturbance that imparts strong cyclonic vorticity to the wind field, with the orographic effect being of secondary importance. During the bora event currents of 70 cm s-1 were measured by drifter movements tracked along the western Adriatic coast. Drifter trajectories for the selected period were simulated by an oceanographic model forced by the outputs of two mesoscale meteorological models, ALADIN and MM5, and by river discharges. The atmospheric models provided realistic space- and time-varying atmospheric fields (wind, air temperature and humidity) with ca 10 km horizontal resolution by ALADIN and with 9 and 3 km by MM5. Several numerical experiments with different combinations of the three forcing agents – wind stress, river discharges and surface heat fluxes – were performed. Proper formulation of the drag coefficient was crucial for the correct simulations of the drifter trajectories, as its increased values do reproduce well the effects of the sea surface roughness and atmospheric stability to the surface ocean layer with respect to the observed drifter movements. Numerical experiments revealed that strong current along the western Adriatic coast resulted from a combined influence of the wind stress and river discharges. The importance of the baroclinic, buoyancy driven contribution to the current field was particularly pronounced in the periods with weak winds. At the same time, drifter movements in the open sea area in front of the eastern Istrian coast were the result of the wind stress acting solely.

Diese Arbeit zielt darauf ab, die raumzeitlichen Regelmäßigkeiten an Übergängen aufzudecken, die in saisonalen Klima- und Ingenieursystemen beobachtet werden, indem moderne Methoden der komplexen Systemwissenschaft verwendet werden. Das erste System ist der indische Sommermonsun - eine Regenzeit, deren jährliche Schwankungen das Leben und den Wohlstand von mehr als einer Milliarde Menschen auf dem indischen Subkontinent beeinflussen und die Wirtschaft des von der Landwirtschaft abhängigen Landes stark beeinträchtigen. Insbesondere die Kenntnis des zeitlichen Ablaufs des Übergangs vom Vormonsun zum Monsun ist für die Planung landwirtschaftlicher Aktivitäten dringend erforderlich. Die Vorhersage des Monsunzeitpunkts über dem indischen Kontinent bleibt jedoch eine große wissenschaftliche Herausforderung. Das zweite ist ein Verbrennungssystem, das anfällig für ein katastrophales Phänomen namens thermoakustische Instabilität ist, das verhindert, dass das Verbrennungssystem unter klimafreundlichen Bedingungen betrieben wird. Eine solche Brennkammer ist typisch für Energie- und Antriebssysteme wie Gasturbinentriebwerke, Boiler und Raketen. Zu verstehen, wann der Übergang zur thermoakustischen Instabilität auftritt und wie dieser Übergang unterdrückt werden kann, sind Schlüsselfragen für die Entwicklung klimafreundlicher Motoren. Diese Dissertation liefert ein neues Verständnis des indischen Sommermonsuns und der thermoakustischen Instabilität durch auf statistischer Physik basierende Ansätze, die verborgene Merkmale in diesen Systemen nahe ihren jeweiligen Übergängen aufdecken., This thesis aims to reveal the spatiotemporal regularities at transitions observed in seasonal climate and engineering systems by utilizing modern methods of complex systems science. The first system is the Indian Summer Monsoon - a rainy season whose yearly variability affects the life and prosperity of more than a billion people in the Indian subcontinent and strongly impacts the economy of the agriculture-dependent country. In particular, knowledge of the timing of the transition from pre-monsoon to monsoon is greatly needed for the planning of agriculture activities. However, the prediction of monsoon timing over the Indian continent remains a significant scientific challenge. The second is a combustion system prone to a catastrophic phenomenon called thermoacoustic instability, which prevents the combustion system from being operated in climate-friendly conditions. Such a combustor is typical in power and propulsion systems such as gas turbine engines, boilers, and rockets. Understanding when the transition to thermoacoustic instability occurs and how to suppress this transition are key questions for developing climate-friendly engines. This thesis provides a new understanding of the Indian Summer Monsoon and thermoacoustic instability through statistical physics-based approaches that reveal hidden features in these systems near their respective transitions.