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Low Water Vapor

Nature Magazine -- NOAA Scientists have observed in the rarefied air over Boulder, Colorado "a significant increase in water vapor concentration in the lower stratosphere." The trend covers the years 1981 to 1994. The NOAA people said it is more evidence of global warming. I was glad to hear that. More evidence was getting scarce.

"Our limited knowledge of water vapor in the upper troposphere and lower stratosphere is one of the great uncertainties in climate modeling. It adds to the concern about the build up of greenhouse gases, climate change and effects on atmospheric chemistry." NOAA scientists commented on their data. That "they are expected to be representative of the stratosphere over the highly populated northern mid-latitudes."

So goes Boulder so goes the highly populated northern mid-latitudes. They say this because the atmosphere at this altitude is well mixed.

In the early 1970s we worried a lot about a high-flying, big bunch of Boeing SSTs, the prototype for the Concord and Concordski. We were concerned for our stratosphere. The water vapor in the jet exhaust would wet the stratosphere and the photochemical models (theoretical metaphysical constructions) said that this water would destroy the ozone layer. At the time it didn't matter that total column Ozone had increased 6% while water vapor in the air over Washington, DC. (1964-1969) Had monotonically gone from about 2 g of water per kg of air to about 3 g of water per kg (see H. J. Mastenbrook (1971) J. of Atm. Sci. 28:1495-1501). So what if the data say the opposite of the models! So we knew at least one place and time where the stratosphere got wetter pronto. Saying it in percentages, like they do on TV, we get: the air got 50% wetter from the 1964 benchmark to 1969. 50% in 6 years =3D 8% per year. Now over Boulder during the 1980s, there was a 1% per year increase in stratospheric wetting. Maybe the air is just getting more wet slower than in the good old days. The interesting thing from Mastenbrook's 1971 paper is that the monotonic wetting from 2 g of water vapor per kg of air to about 3 g of water vapor per kg was present from the bottom of the stratosphere (about the 140 mb pressure elevation) up to 50 MB pressure elevation. So, we might ask the global warming question in the usual way. Does a change at one station indicate a global climate change, after all it makes Nature magazine these days. Well, during the 1960s there was a global cooling if anything, not a warming. During the 1980s the regression line through the Hansen global temperature data set has a slope of zero. The regression line through the Spencer and Christie satellite record of tropospheric temperatures has a zero slope as well. So even if you like to spatially extrapolate from point data to the globe, it doesn't do the dance in this case.

Mastenbrook, after his 1971 paper, followed water content of the stratosphere over Washington DC and was ready to report again on his findings in 1983. From 1964 to 1972/1973 the rise in water content continued as in his 1971 paper. From 1972/1973 to 1982 water content fell back to 2 g of water vapor per kg of air! Hey, it looks like the it-must-be-due-to-global-warming water vapor in the stratosphere exhibits very large, decade scale variations: up and down. The recent report from Boulder by S. J. Oltmans indicates that from 1983 to the present, the water vapor content again was on the increase. Hooking this to global warming at this early date is a real reach but it sells copy. Back in 1983 when greenhouse warming was not the cause of everything, here is how it was reported: the variation in water vapor in the stratosphere was "similar" to the long-term trend in ozone concentration and suggested that "these changes arise from long-term changes in the intensity of the circulation." Since Oltmans wrote the 1983 paper with Mastenbrook, he has apparently changed his mind on the cause of the water vapor variations. Now, one should not get me wrong. Water vapor is the Earth's primo greenhouse gas. It is important stuff. CO2 is a piker by comparisons. Put more water into the stratosphere, top to bottom, and it should retard the progress of earth-light on its way out to space and perhaps warm (limit cooling due to outgoing earthlight) the stratosphere more than otherwise. Well, the Stratosphere, if anything, has cooled a bit in the 1980s. Global warming is indeed a gold mine and claim jumping is great fun at half-the-work but that is how the blame game works.

Hugh Ellsaesser wrote a very nice summary paper titled Stratospheric Water Vapor in J.G.R 88(C6)3897-3906. Hugh indicates that the rise in 1960s water vapor may have begun as far back as 1954 with a very low value of 1.8 g of water vapor per kg of air. Values this low were also reported in the early 1940s by the Royal Air force as it carried frost-point hygrometers with them into the lower stratosphere. The early 1970s values were around 3 g of water vapor per kg of air are then really a big negative change just happened. Hugh's little paper also reveals the mechanism for getting water vapor into the stratosphere and getting it out again. This is the "fountain theory." The great atmospheric convection over the Indonesian maritime continent (part of the El Nino action) "injects" water vapor into the tropical stratosphere. At -80 C and assuming the injection air is saturated, then the air should be injected with about 3 g of water vapor per kg of air. The loss area is in the Polar Regions where the stratospheric air is "downwelled" toward the surface. It is possible that the stratospheric water vapor rise in the post 1982 period may be associated with the great El Nino of 1983 and the very great Indonesian convection the accompanied it. That is the Hayden Theory and the kind of hypothesis for which we have only an N=3D1 basis. I think it is one of the first times I have even hinted at much less blamed anything on the El Nino.

Photo: NOAA



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