Aqua Channel 5 and Short-Term Temperature Variability

Channel 5 data provides a tropospheric temperature estimate every 24 hours. A look at seasonal and interannual variation (see posts) found that the AQUA data, on longer time scales, behaves as-expected at least with respect to seasonality and ENSO. In other words, there is some mid-tropospheric physical realism to the data, so far.

Now it’s time to see how the data behaves over shorter terms (intraseasonal or shorter). There may be interesting things to see which are not visible in the usual monthly averages of global temperature data.

First, here is a time series from the early years of AQUA – 2003. This is a plot of the daily anomalies. (The daily anomalies are calculated by subtracting the “normal” temperature for a date from the 2003 value for that date. “Normal” is defined as the 2003-2010 average of temperatures for a date.)

Perhaps the most apparent visual impression is the “seesaw” or “sawtooth” appearance of the data. Rather than random movement around a central value there appear to be swings in temperature.

The plot contains small red letters “A” thru “G”. The letters designate the peaks of swings over the first six months of 2003. The time between peaks are spaced 22, 23, 26, 24, 23 and 19 days, respectively. The amplitudes vary but are generally in the 0.2 to 0.3 K range, which are rather substantial changes in global tropospheric temperature.

I find the similar spacing and amplitude of these swings to be interesting. What are the underlying physical mechanisms? For example,

*  Specifically, what places the additional heat into the troposphere (or slows the removal of heat) and what triggers that?

*  What is the nature of the decline – is a cessation of whatever caused the rise or is it some negative response whatever caused the rise?

*  Is the warming over a relatively small region, such as a portion of the tropics?

* Does the swing affect the water vapor content of the troposphere and thus its radiative properties? In particular, might the amplitude change with tropospheric temperature?

*  What controls the amplitude of the swings?

*  What controls the timing of the swings – why, in the first half of 2003, did the swings space themselves about 23 days apart?

*  Why are there relatively orderly swings in temperature in the first half of 2003 and not-so-much in the second half?

There is a second interesting aspect in this time series, with examples designated as “H” and “I”. Those are short periods of near-zero tropospheric temperature change.

*  In this 2003 time series with large daily and weekly swings, why are there also periods where the temperature change approaches zero for days? Are those periods simply statistical artifacts or is there some underlying physical cause?

OK. Here is another time series – 2005:

The year shows the saw-tooth appearance of the earlier example (2003) but the 2005 “teeth” aren’t nearly as orderly as was seen in the first half of 2003. The amplitudes of the swings are around 0.2 K to 0.4 K, about the same as in 2003. Of interest are several periods (designated by red letters) in which the global temperature change essentially stops.

*  Why do the 2005 changes appear less orderly than those of the first half of 2003?

Finally for this post, here is a two year period from mid-2009 to mid 2011:

Again, a sawtooth appearance is apparent. Also apparent is the temperature rise and decline associated with changes in ENSO. (The first part of the period was associated with an El Nino event which then shifts into a La Nina state.)

*  The second half of the red line shows a period when Pacific ENSO temperatures were declining rapidly, yet the global temperature remained more or less constant. Why didn’t the troposphere immediately respond to the decaying El Nino and what finally triggered the sharp temperature decline?

*  The green lines suggest a decline in the amplitude of the swings. If that appearance is real and not an artifact, what is the physical explanation of the decline in amplitude?

Summary: there are many interesting things (at least to me) to observe when the daily data is plotted. In future posts I will try to explore some of the questions raised. I am particularly interested in what underlies the rapid temperature changes, including whether these short-duration events are somehow important to the removal of heat from Earth.

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