The European Centre for Medium-Range Weather Forecasts (ECMWF) tends to support
this outlook signalling fresh convergence of flows over the South Peninsula
from August 30 (next Monday). The ECMWF sees the possibility of development of
a follow-up low-pressure area (aside of the prevailing one in West-central Bay
of Bengal basin) and at least two tropical storms over the Northwest Pacific
during this period.
This appears not at all good news for the Commonwealth Games in New Delhi in
early October. However, the mystic of India lies in our unpredictability
and we could well weather it all with great aplomb and surprise to all in
the end. New waves of monsoon storms can continue to prolong the agony of flood
victims in Pakistan. The Atlantic hurricane season, expected to kick in by last
week of August, cast its shadow on the ongoing rehabilitation of earthquake
victims in Haiti. Mumbai has a good chance of being submerged a la 2005,
as all it takes is high tides to combine with high rainfall. The rainy season
opens in South China Sea countries like Philippines and Indonesia with
satellite images showing huge convective clouds over the region, suggesting the
region is one with high disaster vulnerability in the coming days.
There are a number of climatic players involved and when they come together and
reinforce each other, they could cause a wide variety of weather extremes and
consequently natural disasters at an unprecedented global scale. In particular,
La Nina event and a strong Madden-Julian Oscillation(MJO) — a weather
pattern featuring thunderstorms and heavy rainfall that travels around the
equator — are expected to create an unusually active severe weather season.
There is also the impact of the more recently discovered Indian Ocean Dipole
(IOD) that superimpose on the latter. We give a short description of the
influences of these oceanic climatic phenomena:
a. La Nina
Globally, the most significant anomaly in
weather patterns this year is the ongoing shift from El Nino to La Nina
conditions. According to long-term forecasts of Tokyo-based Research Institute
for Global Change (RIGC), the prevailing La Nina condition would be more long
lasting than thought earlier and may continue until early 2012. A 24-month La
Nina condition or more should more than adequately offset the kind of global
warming brought about a relatively strong El Nino 2009/10.
The IRI also found elevated probabilities of the La Nina favourably impacting
not just the ongoing south-west monsoon but the subsequent northeast monsoon as
well. As for expected rainfall trends for September-October-November, the IRI
assessed as high the probabilities for excess precipitation for the entire
western half of the country except the south-west Coast and North India (Jammu
and Kashmir, Punjab, Haryana, Himachal Pradesh and Uttar Pradesh) where it
would be normal. During October-November-December, the north-west is expected
to see the advent of the seasonal winter with a largely normal rainfall
pattern.
Accordingly, this
year would be one of the rare years in India where rainfall is experienced
almost continuously from June to December, which enables bumper agricultural
production in all three cropping seasons. Discounting flooding damages,
economists are predicting between 5-6% growth rate in agriculture production
for fiscal 2010/11 that should catapult the country’s GDP near 10%.
[Note:
Kharif crops are usually sown with the beginning of the first rains in July,
during the south-west monsoon season. The term Kharif means "autumn".
The Rabi crop is the spring harvest also known as the "winter crop. In
between the Rabi and the Kharif seasons, there is a short season during the
summer months known as the Zaid season.]
Other oceanic oscillations like a negative Pacific Decadal Oscillation (PDO)
and Antarctic Oscillation (AAO) act in tandem to reinforce the La Nina
effect as seen similarly during the 1998 and 2008 La Nina seasons. The Arctic
Oscillation (AO) has a significant influence on winter weather in the U.S. —
the northern and eastern U.S., especially — as well as Western Europe. Recent
research has also demonstrated a link between the AO and tropical cyclone
formation during the Atlantic hurricane.
b.
Madden-Julian Oscillation (MJO)
The Australian Bureau of Meteorology (BoM) has said that
the next active phase of the MJO wave would develop over West Indian Ocean from
early to mid-September.
The MJO is an equatorial travelling pattern
in Earth’s atmosphere - a cyclical pattern of slow, eastward-moving waves of
clouds, anomalous rainfall and large-scale atmospheric circulation anomalies
that can strongly influence long-term weather patterns around the world.
According to the BoM, MJO has had perhaps the greatest influence on weather
across southern Asia. The MJO sometimes stalls, weakens, or suddenly
regenerates making forecasting a challenge.
The MJO has a periodicity typically ranging from 30-60 days, involving
variations in wind, sea surface temperature (SST), cloudiness, and rainfall. It
creates large-scale conditions, which are known to favour tropical storm
genesis bringing with it, increased moisture and weakening wind shear.
Alternating between a vast province of moist, stormy air and an unusually dry
patch, the oscillation slowly blows through the tropics, often circling the
globe several times.
Over the last week, the MJO has begun to progress into the Maritime Continent
(Southeast Asian region comprising islands, peninsulas and shallow seas) for
the first time since May. The MJO has a modulating effect on hurricane activity
in the Indian Ocean, the western and eastern Pacific and Atlantic basin. The
MJO contributed to the development of a named tropical storm ‘Mindulle' in the
South China Sea, which since had made a landfall in Vietnam.
Although the MJO signal is strongest in the Indian and western Pacific Oceans,
where it increases the intensity of the Austral Asian monsoon system, it seems
to affect the entire tropical troposphere. It has been estimated that up to
one-half of seasonal variance experienced in the western Pacific Ocean is
attributable to the MJO.
The MJO tends to be most active during El Niño-Southern Oscillation (ENSO) neutral
years, and is often absent during moderate-to-strong El Niño and La Niña
events. The MJO activity during late 2007 and early 2008, which occurred during
La Niña conditions, is unusual but not unprecedented. We are witnessing a
repeat of La Nina 2008/09 - an active MJO and moderate-to-strong La Niña
conditions. There is evidence that the MJO influences the ENSO cycle. It
however does not cause El Niño or La Niña, but can contribute to the speed of
development and intensity of La Niña episodes.
The MJO affects precipitation over the tropical monsoon regions. It also
affects the winter jet stream and atmospheric circulation in the Pacific/North
America region, causing anomalies that can lead to extreme rainfall events. It
can also change summer rainfall patterns in Mexico and South America and
accentuating La Niña influences.
The anomalous rainfall is usually first evident over the western Indian Ocean,
and remains evident as it propagates over the very warm ocean waters of the
western and central tropical Pacific. This pattern of tropical rainfall then
generally becomes very nondescript as it moves over the cooler ocean waters of
the eastern Pacific but reappears over the tropical Atlantic and Indian Ocean.
The wet phase of enhanced convection and precipitation is followed by a dry
phase where convection is suppressed. Each cycle lasts approximately 30-60
days. It is also known as the 40-day wave (or 30-60 day or 40-50 day
oscillation).
“In the simplest terms, the brown areas are sinking air while the green
areas indicate upward vertical motion which often enhances thunderstorms &
can boost tropical development. Brown contours cover much of the Pacific
& notice the lack of convection (blue, yellow & red areas).
Neutral to green contours cover the extreme East Pacific eastward across much
of the Atlantic.
What really stands out is the massive area of green contours over the
Asian continent and note all the thunderstorms. This area correlates
closely with the now very active Asian monsoon including the massive flooding in
Pakistan. Indications are that green contours -- upward motion, in other
words, will be overspreading the Atlantic Basin in the coming weeks. This
coincides with the Madden/Julian Oscillation (MJO) which will become favourable
for tropical (cyclone) development.”
Indian
Ocean Dipole (IOD)
The Indian Ocean is the third largest ocean, representing approximately 20% of
global surface waters. It’s obviously impacted by neighbouring oceans: the
Atlantic, Pacific, and Southern Oceans. It shares the Indo-Pacific Warm Pool
(aka Pacific Warm Pool) with the Pacific.
The Indian Ocean is unlike the Atlantic and Pacific Oceans in one major detail;
the Northern Hemisphere portion of the Indian Ocean is very much limited in
size, while the Atlantic and Pacific Oceans extend northward to interact with
the Arctic Ocean. Yet, for long Indian Ocean was treated as playing a
subordinate role to the "king of climate variations," viz. El
Niño Southern Oscillation (ENSO) phenomenon in the adjoining tropical Pacific.
The discovery of an ocean-atmosphere coupled mode named the "Indian Ocean
Dipole mode" (IOD) by an Indian scientist named Saji Hameed radically
changed prevailing paradigms on the role of the Indian Ocean in the world
climate variability. '
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