Archive for the ‘Natural Variability’ Category

Lines, Sines, and Curve Fitting 14 – more extrapolation revisited

2012 February 16 Comments off

A year ago, I was working through some curve fitting exercises. Girma was advancing his line+sine model as superior to climate modeling partially based on its hight correlation. He had allowed that an equally simple model with a higher correlation than his would be a superior model. I demonstrated 3 variations of an exp+sine model, one for each surface record, each had higher correlation than his. Neither one of us dealt with autocorrelation.

I thought I would make a quick update on that original post. Nothing fancy, just adding the data points for the 2011 annual surface temperature record indexes.
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SST Regions: Tropical West Pacific, 23N-23S, 120E-180E

2011 March 9 Comments off
Next up is the Tropical West Pacific as defined by a bounding box 23N-23S, 120E-180E. There are some issues cropping HadSST2. I noticed it in the NW Pacific as well, but thought it was related to the fact that what should have been the upper row was all ‘NA.’ Gonna have to crack the raster ‘crop’ code open. However, I doubt that a row more or less on the boundaries will materially affect the results.

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SST Regions: NorthEast Pacific 23N-65N, 120E-180E

2011 March 8 Comments off
Next up is the NorthEast Pacific as defined by a bounding box 23N-65N, 100W-180W. Over the weekend, there were some modifications to my first presentation. Inverted the x-axis on the Fourier chart. Formatted the freq text on Fourier chart. Created a preset color scale for the maps. Colors and cuts from HadSST2 map. I also saved off the ERSST annual raster so that I don’t have to recalculate it for each run.

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SST Regions: NorthWest Pacific 23N-65N, 120E-180E

2011 March 3 Comments off
I extend the previous work on global and hemispheric fourier analysis with HadSST2 and ERSSTv3b into regional analysis. First up is the NorthWest Pacific as defined by a bounding box 23N-65N, 120E-180E.

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ERSSTv3b: Global Frequency Analysis

2011 March 1 Comments off

Here we use the same frequency analysis tools used for HadSST2 to look at ERSSTv3b.

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HadSST2: Frequencies in Monthly Data

2011 February 28 Comments off

Forgot to update the Fourier and Morlet Wavelets charts in the previous post with monthly data. So here they are. Large charts ahead.

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HadSSTv2: Global, NH, SH Frequency Analysis

2011 February 25 Comments off

This is a mash-up of some of my previous work with Fourier and Morlet analysis extended to a globally gridded data set for sea surface temperatures, the Hadley SSTv2, available as a NetCDF file here. I used this in a ‘trb‘ script last fall. My current attempt is a lot cleaner. I must be learning something. The gridding and masking techniques here are a precursor to more regional studies.

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Lines, Sines, and Curve Fittings 17 – More Morlets

2011 February 22 4 comments

Natural Variability 1 – One World, Two Cuts

2011 February 15 2 comments

This is a sparse post. It just a test spin on my way to looking for regional trends. Lots of tables, little code.

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Knight 2005: Persistent Natural Thermohaline Circulation Cycles

2011 February 11 Comments off

While the Decadal (Climate) Prediction System not only allows for internal natural variability, it feeds short term predictions (10 yrs or so) into slightly tweaked HadCMv3 model. Nevertheless, the near term decadal warming in the DePreSys doesn’t seem significantly slower than iconic 0.2C/decade IPCC AR4 warming. Nowhere near as slow as the ‘line+sine’ or ‘exp+sine’ “models.” Is there a natural “forcing” strong enough to justify the 60 year sine with ~ 0.1C amplitude (in the GSAT)?

I don’t know. But following a pointer in Smith 2007 (DePreSys), leads to the following paper:

A Signature of Persistent Natural Thermohaline Circulation Cycles in Observed Climate
Jeff R. Knight, Robert J. Allan, Chris K. Folland, Michael Vellinga, and Michael E. Mann
GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L20708, doi:10.1029/2005GL024233, 2005

Abstract: Analyses of global climate from measurements dating back to the nineteenth century show an ‘Atlantic Multidecadal Oscillation’ (AMO) as a leading large-scale pattern of multidecadal variability in surface temperature. Yet it is not possible to determine whether these fluctuations are genuinely oscillatory from the relatively short observational record alone. Using a 1400 year climate model calculation, we are able to simulate the observed pattern and amplitude of the AMO. The results imply the AMO is a genuine quasi-periodic cycle of internal climate variability persisting for many centuries, and is related to variability in the oceanic thermohaline circulation (THC). This relationship suggests we can attempt to reconstruct past THC changes, and we infer an increase in THC strength over the last 25 years. Potential predictability associated with the mode implies natural THC and AMO decreases over the next few decades independent of anthropogenic climate change

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