'Libra Showers'

In an early post here I wrote the following brief description of Tulavarsham (literally "the Showers of Libra"), the Keralan name for the North East or Retreating Monsoon:

"In late October - early November, Kerala experiences a very unique weather regime called 'Tulavarsham' - the mornings are sunny and clear; by midday it gets very sultry and the afternoon sees a rapid and massive buildup of clouds followed by a thunderstorm that clears up in a couple of hours. The evenings are usually clear and humid."

And there are any number of other online pages which repeat: "During Tulavarsham, it commonly rains in afternoons with thunder and lightning".

That the Advancing (South West) Monsoon blows in from the Arabian sea due to the subcontinent getting hyper-heated in summer is no mystery. That the monsoon has to retreat once the temperature gradient levels off and then inverts in autumn is not hard to understand either. The Coriolis force explains why the monsoon advances and withdraws along a South-West to North-East axis rather than a North-South one - undergrad, if not high-school, stuff.

But there remain many Tulavarsham characteristics which need explanation.

First up, why do Tulavarsham showers happen almost exclusively in the afternoons/evenings? Afternoon thunderstorms are quite the norm in equitorial rain forests (this again is school gyan). But there, what happens is local convection with no large-scale *horizontal* currents of air; Thulavarsham is about a large-scale drift of air masses over the entire South Asia.

One could guess: the moisture laden monsoon (the moisture having been collected from the Bay of Bengal) blowing in from the north-east collides above Kerala with the afternoon sea-breeze from the Arabian Sea and this could cause the moist air to abruptly rise and condense into sharp thundershowers.

But there are other issues: Why does it not rain anywhere else on the western coast during Thulavarsham (rainfall is utterly scanty on the coast beyond north Kerala; Bombay, which gets much more rainfall from the main south-west monsoon than most places in Kerala, actually suffers a brief second summer called 'October heat'!)? Why don't the Western Ghats cause a rain-shadow effect over Kerala during Thulavarsham (just like they cast a severe rainshadow over western Tamil Nadu during the South West monsoon)?

The answer to the first question appears to be in the shape of the Indian peninsula - a triangle with apex at Kanyakumari. This shape, coupled to the North-Easterly direction of the withdrawal of the monsoon suggests that over say, Bombay or Goa, the withdrawing monsoon would have hardly any moisture since it would have traveled almost entirely over land. To the south, the Bay of Bengal provides enough water to the withdrawing monsoon to drench the southern half of India's eastern coastline in pretty steady rain (the general behavior of NE monsoon over Chennai is rather similar to that of the SW monsoon over Cochin) - and even after traversing Tamil-Nadu, the NE monsoon winds could have enough moisture left to give Kerala some precipitation.

But one has to understand the role of the Western Ghats better. Why do the Western Ghats have such an asymmetric rain-shadow effect between Kerala and Tamil Nadu( in Maharashtra/Karnataka, the mountains drop sharply to the west coast and slope much more gently eastwards, but on both sides of the Kerala-TamilNadu border they are equally steep)? A possible explanation could lie in the coastal plain of Kerala being a very narrow strip of land; this could allow the sea-breeze to play a major role in causing the residual moisture in NE monsoon to get precipitated over it - on the other hand, the Bay of Bengal is hundreds of kilometers from the Western Ghats and a similar mechanism might not operate on the eastern side during SW monsoon.

A legend from medieval Kerala relates: When he heard that the Portuguese had stealthily made off with some pepper wines, the Zamorin remarked: "Don't worry! They can't take away our 'Edavappathi' (the South-West Monsoon)"

I don't quite agree with Zam. the Edavappathi gives no *exclusive* benefits to Kerala - it gives good rains to Kerala all right but it gives much more copious precipitation to Coastal Karnataka, Konkan (including Goa where the Portuguese were well-entrenched) and so forth. But, the Thulavarsham is a different matter altogether; virtually ignoring the Indian west coast above Kasaragod, it extends the Keralan rainy season almost to December. And this is precisely why Kerala has, by far, the most persistently lush landscapes in the country. One sees drought-resistant scrub and cactus hedges in the countryside near Bombay but they are unheard of anywhere in Kerala except perhaps the farthest fringes. Even Cherrapunji suffers from a continuous rainless spell of 6 months, leading to near drought conditions every year; in Kerala the 'dry window' lasts just about a third of that!

Watching the rapid buildup and awesome approach of a Tulavarsham thunderstorm from the Ishanya (North East) corner of the October sky, one can't help recollect the inspired imagery of medieval Keralan poet Poonthanam's hymn addressed to Kali (Thirumandhankunnil Amma):

"Ghanasangham idayunna thanukanthi thozhunnen!"

("I behold and salute thy fearful form, a vision of dark, swirling rainclouds in thunderous collision!")

Three Eggs

1. AN EGG FROM ANTARCTICA

This egg originally belonged to an emperor penguin in Antarctica and was found - and flicked - by a certain Mr. Apsley Cherry-Garrard and his group back in 1910. The story is very briefly told in http://www.guardian.co.uk/uk/2012/jan/14/penguin-eggs-worst-journey-world

The quest for the penguin's egg was an attempt to marshall evidence for an early theory on embryogenesis and evolution. Despite the heroism shown and sacrifices made by the seekers (and for some of them, the sacrifice was the supreme one), most accounts mark their efforts as ultimately quite futile - the eggs did not yield the kind of data anticipated and the theory they were trying to establish had to be discarded (An insensitive way of putting it in Malayalam would be: "the theory yielded an elephant's egg!").

2. VIRABHADRA RAO'S EGG

The story of Virabhadra Rao's Egg has many more horrible deaths than the penguin's. Still, it is an altogether more funny one!

Sometime around 1940 in Madras, a certain young scientist named Virabhadra Rao began a study of the embryology of a certain species of sea slug called 'kalinga ornata' (aside: wonder what this animal has to do with Orissa!). The project faced severe initial difficulties as the slug species is hard to obtain. After plenty effort, Rao finally found an adult specimen and kept it in a stone trough in a big lab that he shared with several other scholars, all engaged in the study of various marine species. The lab had a large collection of live specimens in glass vessels and troughs. A certain colleague of Rao's noted how pleased everyone was to see the newbslug peacefully creeping around the bottom of its new home.

The next day morning, everyone was in for a profound shock. The water in every container had turned into something like thick 'kanji' and most specimens were dead, chocked in the slimy mess. And there was a foul smell in the air. In Virabhadra Rao's trough, there was no trace of his slug!

During the sad cleanup, an attendant spotted the slug at the bottom of another trough in a far corner of the lab; it was quite alive and a thin sticky thread rapidly issued forth from its belly. "It has caught diarrhoea!"

It took a while for Rao and friends to figure out what was happening. The slug was laying eggs - millions and billions of them - in an unending stream. It first filled its 'home trough' with eggs and then crept out and crawled into the next trough and then to the one beyond it and so on, laying eggs constantly and souping up the water in each vessel. Despite its having been at it for perhaps the entire night, there was no sign of a letup. The older eggs had already begun to die and decay - raising the stink.

Soon thereafter, the phrase 'Virabhadra Rao's egg' came to mean "foul, sticky mess" in the group. As a good friend of his(*) remarked, "Rao is a neat and meticulous chap. Sad irony, his name got associated with utter filth"

3. The PERUNTHACHAN EGG

This egg has yet to be clearly seen and sized up. Indeed, it has yet to be sought with anything approaching Cherry-Garrard levels of intensity; and to be honest, even its existence is not yet confirmed. On the flip side, it has yet to record a kill!

Sometime back, I wrote here about the geometry problem of finding that convex planar figure (let me call this C) from which when two mutually congruent convex shapes of largest possible area are cut, the highest fraction is still left over. Some experiments indicated C has to be a smooth and fat figure (details are here: http://arxiv.org/abs/1012.3106) and I proposed the name 'Perunthachan Oval'for it - among other things, as a homage to Kerala's legendary master-craftsman.

To my knowledge, no further work has happened anywhere on this problem. So, the Perunthachan oval now exists only in my fond hopes. But I hereby go one level up and christen its 3d analog, the 'Perunthachan Egg' - at least its logical continuity from 'oval' is indisputable!

Moreover, this egg has the potential to be the first ever Mathematical object named solely after a Mallu - only the first half of the (admittedly, much better established)'Madhava Gregory series' belongs to Kerala!

Correction (Jan 2013): Am surprised to note that there is a very modern Mathematical concept named after a Keralan mathematician I have been privileged to have met. Here it is: http://en.wikipedia.org/wiki/Nambooripad_order

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(*) Virabhadra Rao's friend who recorded the slug-saga for posterity was K. Bhaskaran Nair (1913-1982) - zoologist, teacher and author. In his time, he was considered a preeminent master of scholarly Malayalam prose. And his 'Atta akashathekku' ('Astronaut Leeches') is a jewel of a popular science (mostly biology) work, ranking right up there in the Gould-Attenborough class. Unfortunately, Mallus have not remembered his contributions well. He has no wiki presence; google with "K.Bhaskaran Nair" and almost all pages popping out will be on a namesake of his who was a comic film actor of moderate to tolerable calibre.

And almost a lifetime after Rao's investigations, his slug continues to puzzle researchers - wiki says: "little is known of its biology"