Today's entry is the second in an ongoing series on radiative cooling for the tropics and is mainly for readers who understand psychometric charts. I show today's very typical hot season trajectory of Bangkok air properties from dawn to mid afternoon (red arrow) superimposed on a handy old chart I use to aid my judgment on matters of thermal comfort. The daily process is essentially isenthalmic (constant-enthalpy). Our Bangkok day is way outside of US standards of comfort (with which I disagree) and also within the "danger zone" (justifiably so) that was established by the US military after scandalous heat deaths of marine recruits during basic training. Having also done my basic training in the sweaty Virginia summer near Richmond, I am proud to have survived at least the heat battle of a forced march before reforms were instituted (but I recall an ambulance did trail our ragged column), though I never did hear a shot fired in Vietnam.
Today's Bangkok wet bulb temperature (surrogate for enthalpy) was 28C (82F). Wet bulb temps above 30 were recorded with deadly results in Pakistan last year and are considered very dangerous in military training. The wet bulb temp should be close to the surface sea temp (also 28 in the Gulf of Siam as recorded yesterday) and has never been seen to exceed 35. Wet bulb temps of about 32-33C have been recorded in Bangkok and also (surprisingly) in the middle of cornfields in Appleton Wisconsin. Our wet bulb today is about at the 1% summer design level for US hotspots such as Pensacola, Galveston, and El Centro.
Note from the chart that the afternoon and evening dew point temperatures drop to about 25C and relative humidity to 50% so a cooled surface at that temperature would not attract condensation.
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