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Monday, June 26

Halfway through the year we have already set new heat records in Middle East, USA

"The heatwave in May that covered northern India, central Pakistan and eastern Iran created a new world record."

Summary of the Great Southwest U.S. Heat Wave of 2017
Dr. Jeff Masters
June 24, 2017, 1:10 AM
Weather Underground

The great Southwest U.S. heat wave of 2017 is gradually diminishing, but it has left behind hundreds of smashed heat records, including at least four all-time hottest temperature marks for major stations. According to wunderground weather historian Christopher C. Burt, this week’s event has been the most intense heat wave yet recorded to affect the Southwest so early in the summer, coming about a week earlier than the previous great June heat waves that have affected the Southwest, like those of 2013, 1990 and 1994.
[...]
The multi-day nature of this heat wave has been adding to it's dangerous nature: prolonged heat waves are especially hazardous because there is less chance for people to cool down by night, thus increasing the stress on those who do not have access to air conditioning.
[...]
This week's heat wave brought high levels of ground-level ozone pollution to the affected region. Ground level ozone, which is created from chemical reactions between volatile organic carbon (VOC) compounds and nitrogen oxides in the presence of sunlight, is created more readily at warmer temperatures. The heat wave’s record heat helped these chemical reactions occur faster, resulting in ozone pollution that topped out in the “Unhealthy” range in the valleys of California.
[...]
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June 26, 2017
Al  Jazeera 

Figures verified by Maximiliano Herrera
With thanks to Jeff Masters et al at Weather Underground

At the current rate of progress, 2017 will turn out to be the second hottest year since 1880, when the recording of global temperatures started.

2016 was boosted a little by El Nino which would make it even more remarkable were 2017 even to be ranked second because El Nino has gone for now.

So far this year world records have been broken in both high temperature and low humidity.

The heatwave in May that covered northern India, central Pakistan and eastern Iran created a new world record. Turbat in Pakistan recorded 53.5C on May 28, the new highest May temperature in the 137 year continuous list. It was also the highest temperature recorded for any month, in Pakistan.

Then, on June 20 in Death Valley, California, the thermometer read 52.5C, making it the highest temperature measured in the Western Hemisphere, so early in the year.

Hot days are more bearable if the nights are significantly cooler. Indeed that differential is often what determines the existence of a deadly 'heatwave'. Temperatures this high are rarely accompanied by cool enough nights and on June 17, Khasab in Oman set another world record: 44.2C became the highest night minimum temperature on record.

From a human point of view, such hot weather is only survivable if the humidity of the air is low enough for the body to cool by evaporation of sweat. Luckily for us, this always the case on this planet, in normal circumstances. Sometimes the humidity is extraordinarily low as it was this month in Iran and the desert US.

Safi-Abad Dezful in Iran measured less than 0.4 percent relative humidity on June 27 with a temperature of 46.5C. This effectively ties with Needles, California for the lowest known relative humidity reading on earth. The California reading was made in May 2014 but on June 20 this year Needles was as dry as 0.8 percent.

For readers in the Middle East, when the temperature is in the middle 40s during the summer, the typical RH is around about 10 percent. That is why it is possible to be outside even though that heat is above body temperature. Perspiration works to keep us cool enough in those conditions. This is often called 'dry heat'.

Relative humidity, RH, is the measure of how much water vapour is in the air compared with how much would be needed to saturate that air and form fog.

Hot air can carry more water vapour than cold air so using relative rather than absolute humidity allows a comparable figure at any temperature.
[END REPORT]
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