AEROSOLS : What Do They Have to Do With The Indian Heat Wave 2015?

That was a tense Indian summer which intense heat waves smashing the country. What makes it “record breaking”?

Delhi roads melting due to intense heat waves (abc7news.com)

See this? Petrified? So was I…The intense episode of 2015 Indian heat wave hit the list of top 5 deadliest heat waves! This is not new though. So, you ask, why are we talking about this now if this has been a tradition in India, every summer?

Guess what?? “Recent increase in the frequency, persistency, and spatial coverage of heat waves when compared to 1970s”, quote a few articles. This could be a close resemblance to more intense heat waves in future.

In general, heat waves are affected by numerous factors ranging from large scale meteorological patterns and local aerosol effects. What intrigued me was the effect of aerosols on these heat waves in Indian megacities like Delhi and Hyderabad.

You ask, who cares about the small particles that exist less than a week?…Now, walk outside, lift your eyes, watch the beautiful sky if you are lucky… most likely , if you are like most of us, living in megacities, you might be looking out on veil of smoggy particles or coarse dust and pollen.. And that’s what I’m talking about – AEROSOLS ! 

Aerosol sources (Image courtesy : caice.ucsd.edu)

That got me thinking about some specific questions and hypothetical reasoning regarding the heat waves in Delhi and Hyderabad.

a) ‘How local effects of pollutants, especially, aerosols (e.g. dust, black carbon particles) alter the intensity of heat waves?

Hypothesis: Well, this is a familiar one. Aerosols like Black Carbon (BC : in simple terms, the smoke you see in a burning candle and the black smoke you see out of a vehicle hold BC particles.) absorb radiation from the atmosphere and re-emit that radiation and transfer the heat back to the atmosphere. This can act like a SELF AMPLIFYING EFFECT to the heat waves, therefore increasing their intensities.

b) Now, let’s take a step back and turn the question around. Imagine this sweltering heat and lower wind speeds which is usually the case during heat waves, what happens to aerosols in that region? They accumulate due to lower wind speeds. If they are absorbing aerosols like BC, they have a feedback to the heat waves, THUS CAUSING THE SELF AMPLIFYING EFFECT.  

Delhi, being a megacity, the effects of increased urbanization can cause wind stagnation and low horizontal transport of pollutants.

C) What is the probability of a year experiencing a heat wave in the study area given the local effects of aerosols?

If we consider this aerosol heat wave feedback into the system, will the heat wave intensity significantly increase in future years, if we increase the load of aerosols?

Well, in terms of global warming, these are much familiar questions. We know human induced pollution has a huge impact on surface temperature changes across the globe. But, what appears as a tangential question is, “how do these short lived pollutants affect the intensity of episodic heat waves that last only for a couple of weeks?”

I’ll let you guess the details until a later post how these hypotheses can be tied to the Indian heat wave case study in Delhi.