From Dr. Roy Spencer’s Weblog
October 4th, 2019 by Roy W. Spencer, Ph. D.
Whereas the overwhelming majority of our month-to-month world temperature updates are fairly routine, September 2019 is proving to be a singular exception. The underside line is that there’s nothing unsuitable with the UAH temperatures we initially reported. However what I found about final month is fairly uncommon.
It began when our world decrease tropospheric (LT) temperature got here in at an unexpectedly excessive +Zero.61 deg. C above the 1981-2010 common. I say “surprising” as a result of, as WeatherBell’s Joe Bastardi has identified, the worldwide common floor temperature from NOAA’s CFS mannequin had been operating about Zero.three C above regular, and our numbers are normally not that completely different from that mannequin product.
[By way of review, the three basic layers we compute average temperatures from the satellites are, in increasing altitude, the mid-troposphere (MT), tropopause region (TP), and lower stratosphere (LS). From these three deep layer temperatures, we compute the lower tropospheric (LT) product using a linear combination of the three main channels, LT = 1.548MT – 0.538TP +0.01LS.]
Yesterday, John Christy seen that the Southern Hemisphere was unusually heat in our decrease stratosphere (LS) temperature product, whereas the Northern Hemisphere was unusually cool. This led me to have a look at the tropical outcomes for our mid-troposphere (MT) and ‘tropopause’ (TP) merchandise, which within the tropics normally observe one another. A scatterplot of them revealed September 2019 to be a transparent outlier, that’s, the TP temperature anomaly was too cool for the MT temperature anomaly.
So, John put a discover on his month-to-month world temperature replace report, and I added a discover to the highest of my month-to-month weblog submit, that we suspected perhaps one of many two satellites we’re at present utilizing (NOAA-19 and Metop-B) had issues.
Because it seems, there have been no issues with the information. Simply an uncommon regional climate occasion that produced an uncommon world response.
Blame it on Antarctica
A few of you might need seen information stories a number of weeks in the past sturdy stratospheric warming (SSW) occasion was anticipated to kind over Antarctica, probably impacting climate in Australia. These SSW occasions are extra frequent over the Arctic, and happen in winter when (put very merely) winds within the stratosphere move inward and power air inside the chilly circumpolar vortex to sink (that’s referred to as subsidence). Because the stratosphere is statically steady (its temperature lapse charge is almost isothermal), any sinking results in a robust temperature enhance. CIRES in Colorado has offered a pleasant description of the present SSW occasion, from which I copied this graphic displaying the vertical profile of temperature usually (black like) in comparison with that for September (pink line).
By mass continuity, the air required for this large-scale subsidence should come from decrease latitudes, and equally, all sinking air over Antarctica have to be matched by an equal mass of rising air, with temperatures falling. That is half of what’s referred to as the worldwide Brewer-Dobson circulation within the stratosphere. (Observe that as a result of all of this happens in a steady surroundings, it isn’t ‘convection’, however have to be pressured by dynamical processes).
As could be seen on this GFS mannequin temperature discipline for in the present day on the 30 mb degree (about 22 km altitude) the SSW continues to be in play over Antarctica.
GFS mannequin temperature departures from regular at about 22 km altitude within the area round Antarctica, 12 UTC four October 2019. Graphic from WeatherBell.com.
The next plot of each Arctic and Antarctic UAH LS temperature anomalies reveals simply how sturdy the September SSW occasion was, with a +13.7 deg. C anomaly averaged over the realm poleward of 60 deg. S latitude. The LS product covers the layer from about 15 to 20 km altitude.
As talked about above, when one in every of these heat occasions occurs, there’s cooling that happens from the rising air on the identical altitudes, even very far-off. As a result of the Brewer-Dobson circulation connects the tropical stratosphere to the mid-latitudes and the poles, a change in a single area is mirrored with reverse adjustments elsewhere.
As proof of this, if I compute the month-to-month adjustments in decrease stratospheric temperatures for a couple of completely different areas, I discover the next correlations between areas (January 1979 via September 2019). These detrimental correlations are proof of this see-saw impact in stratospheric temperature between completely different latitudes (and even hemispheres).
Tropics vs. Extratropics: -Zero.78
Arctic vs. S. Hemisphere: -Zero.70
Antarctic vs. N. Hemisphere: -Zero.50
N. Hemis. vs. S. Hemis.: -Zero.75
Due to the extreme stratospheric warming over Antarctica, it brought about an unusually massive distinction within the NH and SH anomalies, which raised a pink flag for John Christy.
Subsequent I can present that the SSW occasion prolonged to decrease altitudes, influencing the TP channel which we use to compute the LT product. That is vital as a result of sinking and warming on the altitudes of the TP product (roughly Eight-14 km altitude) may cause cooling at those self same altitudes very far-off. This seems to be why I seen the tropics having the lowest-ever TP temperature anomaly for the MT anomaly in September, which raised a pink flag for me.
On this plot of the distinction between these two channels [TP-MT] over the Antarctic, we once more see that September 2019 was a transparent outlier.
Conceptually, that plot reveals that the SSW subsidence warming extends down into altitudes usually thought-about to be the higher troposphere (in line with the CIRES plot above). I’m assuming that this led to uncommon cooling within the tropical higher troposphere, resulting in what I believed was anomalous knowledge. It was certainly anomalous, however the purpose wasn’t an instrument downside, it was from Mom Nature.
Lastly, Danny Braswell ran our software program, leaving out both NOAA-19 or Metop-B, to see if there was an uncommon distinction between the 2 satellites we mix collectively. The worldwide LT anomaly utilizing solely NOAA-19 was +Zero.63 deg. C, whereas that utilizing solely Metop-B was +Zero.60 deg. C, which is fairly shut. This basically guidelines out an instrument downside for the unusually heat LT worth in September, 2019.