Chuck Wiese is the best meteorologist I know. Last year, he retired from flying the big jets for Delta Airlines. – Ed
by Chuck Wiese, Meteorologist
With the continued and terrible politicization of atmospheric science and climate, I thought I would take a look at the true cause of this historic Pacific Northwest heat wave we just experienced that is now being terminated west of the cascades by a strong push of marine air from off the ocean.
For starters, the synoptic weather pattern that set itself up over our region was handled quite well by the short-term numerical weather forecast models. Before the onset, we saw nearly identical pressure patterns forecast to generate as we typically see with our severest high temperatures. In the climate records, those for Portland were found to occur on July 30, 1965, and both August 8th and August 10th of 1981 at 107 deg F.
These records occurred at the Portland National Weather Service Office located then at the Marine Drive location at the Portland International Airport. The complete records in Portland go back to 1940 for the airport location and downtown Portland back to 1890, but these records at the airport exceeded or equaled any of the records in the downtown location. So they were considered all-time records back to 1890.
So at the peak of this heatwave in Portland which was yesterday, the maximum temperature reached 116 deg F, a new all-time high-temperature record going back to 1890. Several other all-time records were established as well in Oregon and Washington.
This is astonishing if you are caught off guard into believing the old records could not be broken by an obscure factor most meteorologists don’t think about on a day-to-day basis. It’s summer, and so pressure patterns that generate the heat were thought of as a comparative to old records with identical synoptic set-ups.
This is at least how I looked at things initially along with others who saw the “suspiciously high-temperature forecasts” given by the numerical model prediction output that actually forecasted the extreme temperatures accurately.
These only became believable as the model output became repetitious in several runs as we got within 2 days of the expected extreme temperatures. This is common practice in operational meteorology to become suspicious of model output extremes especially since we have seen many occasions where extremes in temperature or precipitation given by models back off from those predictions and self-correct within a couple of days of an extreme event. But it turns out the numerical model output in this situation was correct several days in advance.
Why was this? What caused the extremes? Was it really “climate change” related to atmospheric CO2 as some are claiming or was it something else? When I looked into the specifics, it turns out that “climate change” or atmospheric CO2 had nothing to do with this heatwave.
First off, I looked at the “greenhouse gases”. The water vapor optical depths of the 1981 heatwave and today’s extremes were nearly identical as taken off the atmospheric soundings from Salem, OR. So it was not that.
What about atmospheric CO2? In 1981, the Mauna Loa CO2 level was given as 341 ppmv whereas today it is 416 ppmv. Calculating the change in radiative forcing from CO2 as a stand-alone constituent, the difference from 1981 to now is only 1.07 Wm-2. ( Watts per square meter ).
Next, I took the mean temperature of the daily temperature delta or deviation, which was about 90 deg F and plugged that into the derivative of the Stefan Boltzmann equation, dF/dT which gives 6.45 Wm-2K-1 or 6.45 Watts per square meter per degree Kelvin.
Using this relationship, if CO2 acts alone as permitted in this special case, we get 0.963 Wm-2 with a ground emissivity of 0.9 divided by the rate of change of flux with respect to temperature or the 6.45 Wm-2K-1 number which gives 0.15 deg C or a possible contribution of +0.27 deg F. to the heating total.
So CO2’s contribution to this heatwave is far too small to even move the thermometer upwards from the 107 deg F old records to a measurable whole degree F. This is not even measurable with many of the degree of accuracy specifications on many thermometers.
But if you examine the solar radiation dynamics, you get an entirely different picture that explains how we achieved the new records and these numbers were obviously incorporated into the numerical weather model outputs several days in advance. It is important to recognize that when we compare the old records to the new, the atmospheric dynamics in 1965, 1981, and today were nearly identical, meaning the subsiding air that sets the convective temperature cap or potential temperature of the surface started the same.
This dynamic is what the TV guys were calling the “upper air heat dome” to simplify the concept to the layperson. But the timing of these heatwaves was different. In 1981, they occurred in the first week of August and at the end of July in 1965. Today, we are at the end of June or just past the summer solstice or highest sun angle of the year. It turns out this difference of dates is a big deal and actually explains the severity of this heatwave and new maximum temperature all-time records when combined with the upper air dynamics.
The solar radiation reaching the earth’s surface can be calculated anywhere from the relation:
sin( beta) = cos(L) cos( delta) cos (H) + sin(L) sin ( delta ),
where beta is the solar angle above azimuth or the horizon being solved for, L is earth latitude, delta is the declination angle of the earth to the solar ecliptic plane and H is the hour angle, taken as 15 degrees per hour from solar noon.
By hours or minutes, the sum or integral of the solar radiation can be calculated with the initial condition that the undepleted radiation approaching the surface is roughly 70% of the solar constant at the normal plane 90 degrees perpendicular to the earth’s atmosphere, where the sun is directly overhead an observer on the ground.
The average of the solar “constant” is 1,366 Wm-2 but varies through the year by +/-3% due to the elliptical orbit of the earth around the sun, and reaching the highest value at the winter solstice in the Northern Hemisphere. This change can be calculated directly from the inverse square law of radiation intensity vs. distance.
Using 46 degrees of latitude for Portland, the daily transmitted solar radiation to the surface on June 27th is 2.4894800 x 10^7 Jm-2. ( Joules per square meter ) Over a 15 hour solar day, the average solar radiation transmitted to the surface is 461 Wm-2.
On August 8th, the total surface radiation is 2.0920000 x 10^7 Jm-2 and likewise, over a 14-hour solar day gives an average surface solar insolation of 415 Wm-2. The difference between these two numbers is substantial at a whopping 46 Wm-2!
But this difference is mitigated some due to the elliptical orbit of the earth around the sun which between June 27th and August 8th adds an additional 8 Wm-2 of solar insolation to TOA or 6 Wm-2 to the surface at the perpendicular angle to the atmosphere. With the noon solar angle of the sun calculated at 60.49 degrees above azimuth on August 8th, that reduces those values further at Portland’s latitude to 5.2 Wm-2, with the final difference in solar radiation being 40.8 Wm-2 further reduced to 36.72 Wm-2 with a surface emissivity of .9. This is still quite substantial.
If we divide this difference into the rate of change of flux with respect to temperature of 6.45 Wm-2K-1 given above, we get a surplus temperature of 5.69 deg C or 10.2 deg F compared to the earlier heatwaves of record on July 30, 1965, and on August 8h and 10th of 1981. Add this to these old records of 107 deg F and you get 117.2 deg F. That comes within 1.2 degF of what the new all-time high-temperature record is that was just set for Portland at 116 deg F yesterday.
Around the area, it’s obvious there could never be a perfect prediction using this alone, as the surface canopy around the Portland metropolitan area and surrounding cities has numerous variations that shade part of the canopy at all times while some surfaces have lower and higher specific heats than what is next to them, creating small variations of microclimates that are mixed by wind currents to give a final deterministic temperature.
But the point in all of this is clear. Solar radiation was the clear driver that caused these new all-time temperature records and little else.
Now a word about “heat domes”. We must remember these systems are NOT created by greenhouse gases! They are connected by the dynamic westerly wind belt surrounding the earth that has the jet stream winds contained within it. This means the creation of a “heat dome” is directly proportional to the strength of the low-pressure systems upstream or downstream or both and those are also referenced as the “cold” areas of low pressure aloft.
Further, it is the low-pressure system generation that causes the strength of the high-pressure system and its residing subsidence that creates the “heat dome” within the high pressure. So a stronger heat dome means a stronger low pressure and a stronger low-pressure system is fed by COLD air from high latitudes being accelerated southward by the decreasing Coriolis force associated with northerly winds.
This comes about from the theory of planetary Rossby wave physics and the subsequent tie to the Sutcliffe development equation that describes the vertical accelerations of wind that advects atmospheric mass upward and downwind from the low-pressure centers to create the high-pressure systems and “heat domes”.
So it should be clear from all of this, that if atmospheric CO2 truly caused the climate to change, that the temperature extremes we just experienced would not be possible because the gradient of temperature across the latitude lines would lessen, thus reducing the potential energy otherwise available to generate low and high-pressure systems.
The physics of this demand that the storms and high-pressure systems weaken, thus reducing the subsidence or strength of the “heat dome” thus setting the potential temperature of the surface LOWER, not higher, as the incorrect climate propaganda tries to assert, and further, the mean position of the jet stream MUST migrate to higher latitudes causing the distribution of atmospheric mass and pressure to become more uniform across the earth, decreasing average worldwide wind speed.
This means extreme weather of every kind inclusive of temperatures would be lessened, but the mean earth temperature would be increased to warmer. Worldwide drought would also become a symptom of this, not regional drought that we now experience and that is part of ocean cycles that drive the Pacific Decadal Oscillation (PDO).
This does not fit anything we are seeing happening today. These strong high-pressure systems are an indication of a robust supply of cold air at higher latitudes given the season which we see on the daily weather maps and it is noteworthy again that global air temperatures are at only +0.08 deg C over the 30-year mean. The global air temperatures have cooled sharply since the beginning of this year due to the La Nina conditions of the tropical Pacific.
It is also worth noting that these pressure patterns are created through chaotic and random variation within the atmospheric system and are not predictable in general terms more than about a week ahead of time with any reliability. It is unlikely we will see any repeat of this pattern within the next week to 10 days and no assurance that this warm and hot weather pattern will even persist for the latter part of the summer.
Sometimes the summers can end cooler and wetter and other times hot and dry like now. There is simply no predictability to this except in very general terms as related to the ocean cycles and they are not even correct at all times. But from this data, a later summer heatwave will never reach the records we just set.