India's Variant Weather cover

Vol no. 15 Issue No. 93

Inside this issue

India's Variant Weather

India’s Weather extremes

By: L S Rathore, D R Pattanaik and S C Bhan

Being a land with a unique climatic regime, including two monsoon seasons, two cyclone seasons, hot and cold weather seasons, cold waves and fog, India is vulnerable to several extreme weather events. A spatio-temporal analysis of these weather extremes is extremely essential to help understand India’s vulnerability potential, and hence minimise the adverse impacts on the population.

The Monsoon

By: Staff Reporter

The term monsoon is customarily used in the South Asian context to refer to a period of widespread rains during June-September, otherwise known as the ‘Indian summer monsoon’. The common reference to a ‘good’ or ‘bad’ monsoon denotes whether the rainfall is in excess or deficient over a large area like India. While the monsoon has a wider economic and socio cultural importance for South Asia, its origins have been subject to much scientific debate.

Tropical Cyclones

By: Ajit Tyagi

A tropical cyclone is an intense low pressure system that is classified on the basis of its wind speed. The phenomena has a definitive structure and a well-defined life cycle.

The Science behind the Tamil Nadu Floods

By: J R Kulkarni

Tamil Nadu experienced unprecedented floods in November-December 2015, with Chennai bearing the brunt of non-stop rains and inundation paralysing normal life. High sea surface temperatures over the Bay of Bengal, a stationary pressure trough and easterly waves caused this phenomenon.

Floods

By: Staff Reporter

Floods refer to the overflowing of a river or water body beyond its normal confines. They may take the shape of flash floods, surface floods, rapid onset or slow onset floods, depending on the manner of their occurrence.

The Chennai 2015 Floods

By: Surya Parkash

The Chennai floods in November-December 2015 are a wake-up call for us all. It is high time we stopped all unregulated unauthorised illegal encroachments and constructions over natural watercourses, creeks, estuaries, ponds, lakes and marshlands in our greed to over-exploit our natural resources under the ruse of development.

Droughts in India

By: Staff Reporter

Drought is a deficiency in precipitation for a season or more, resulting in water shortage. Droughts may be meteorological, agricultural or hydrological. Depletion of tree cover can combine with scanty rains to increase the magnitude of a drought.

Heat Wave

By: Staff Reporter

In the last few decades, there has been an increasing incidence of high-humidity heat waves. Human-induced climate change has been proved to be the major factor behind the increased frequency and severity of heat waves all over the world.

Cold Wave

By: Staff Reporter

As India braces itself for another cold wave this winter, its dynamics are explored in a brief treatise. The cloudiness, fog, precipitation and more are decoded for quick understanding and greater preparedness.

Hailstorms

By: Staff Reporter

A hailstorm is a thunderstorm that produces ice as precipitation. Hailstorms can cause serious damage to crops and property. In India, hailstorms mostly affect the northeast and western Himalayas, with the maximum strikes in March and April.

Extreme event prediction, a priority research

By: Staff Reporter

Madhavan Nair Rajeevan, the Secretary, Ministry of Earth Sciences, spoke with Sulagna Chattopadhay from within the precincts of his new office, providing an excellent overview of a possible link between increased extreme events and climate change.

Wettest Place in the World: Mawsynram

By: Ajit Tyagi and P Guhathakurda

Mawsynram, has currently overtaken Cherrapunji as the wettest place on earth. But both these places in Meghalaya’s East Khasi hills share a common orography, although facing different valleys.

Thunderstorm

By: Staff Reporter

Thunderstorms are localised phenomena that can cause substantial damage. These are classified into the ordinary or single-cell, long-lasting multiple-cell or violent super-cell ones. In India, the pre-monsoon season is when most thunderstorms occur.

India's Outdoors

The Chambal

By: Sumit Chakraborty

The Chambal National Park is a rare, unspoilt place off the tourist circuit where you can enjoy the sight of the Indian gharial, and flocks of Indian skimmer in their natural habitat.

In brief

Editor's Note

In the current decade, substantial change in the frequency and intensity of extreme events may be seen, with heat waves, floods, cyclones and more occurring in a grim cycle of climate related disasters. The pattern of precipitation too has changed, with fewer light and moderate rains being replaced

Guest Editor's Note

Extreme weather events causing natural disasters in the current decade are occurring nearly five times as often as they were in the 1970s. The frequency of geophysical disasters—earthquakes, tsunamis, volcanic eruptions and mass movements, remained broadly constant throughout this period, but a su

Term Power

What is ...

The Baroclinic areas in atmosphere are generally found in the mid-latitude/polar regions whereas the Barotropic zones of the Earth are generally found in the central latitudes, or tropics.

Is the largest element of the intra-seasonal variability in the tropical atmosphere. In 1971 Roland Madden and Paul Julian stumbled upon a 40-50 day oscillation when analysing zonal wind anomalies in the tropical Pacific. The MJO, also referred to as the 30-60 day or 40-50 day oscillation, turns out to be the main intra-annual fluctuation that explains weather variations in the tropics.

An overflow of a large amount of water beyond its natural limits, especially over a normally dry land.

Hydrological drought is associated with the effects of periods of precipitation (including snowfall) shortfalls on surface or subsurface water supply (i.e., stream flow, reservoir and lake levels, groundwater). The frequency and severity of hydrological drought is often defined on a watershed or river basin scale. Although all droughts originate with a deficiency of precipitation, hydrologists are more concerned with how this deficiency plays out through the hydrologic system.

The Standardized Precipitation Index (SPI) is a tool which was developed primarily for defining and monitoring drought. It allows an analyst to determine the rarity of a drought at a given time scale (temporal resolution) of interest for any rainfall station with historic data. It can also be used to determine periods of anomalously wet events. The SPI is not a drought prediction tool.

The Dipole Mode Index is an indicator of the east-west temperature gradient across the tropical Indian Ocean, linked to the Indian Ocean Dipole or Zonal Mode.

The Indian Ocean Dipole, also known as the Indian Niño, is an irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean.

El Niño Southern Oscillation (ENSO) is an irregularly periodical climate change caused by variations in sea surface temperatures over the tropical eastern Pacific Ocean, affecting much of the tropics and sub-tropics. The warming phase is known as El Niño and the cooling phase as La Niña.

Western Disturbance occurs in India, Pakistan, Karnataka and Nepal to describe an extra-tropical storm originating in the Mediterranean, that brings sudden winter rain and to the north-western parts of the Indian subcontinent. This is a non-monsoonal precipitation pattern driven by the Westerlies.

The Hadley cell, named after George Hadley, is a tropical atmospheric circulation which features rising motion near the equator, poleward flow 10-15 kilometres above the surface, descending motion in the sub-tropics, and equatorward flow near the surface.

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