Monthly Archives: May 2018

3-year trends to May 2018

Posted in 3-year climate trends, Manilla NSW by

Warm and Very Dry

3-year trends to May 2018

May raw anomaly data (orange)

The raw maximum temperature anomaly for May 2018 was rather high, as was that of the subsoil. The anomaly of daily minimum temperature was low. Very low moisture was shown by the rainfall, daily temperature range, and dew point anomalies, but cloudiness was normal.

 Fully smoothed data (red)

Fully-smoothed data are now available for the spring months (SON) of 2017. In that season, all three temperatures were within their normal range. Both air temperatures were rising, but subsoil temperature was falling.
Rainfall was moving up the graph to less than normal (i.e. arid). The other three moisture measures were moving down their graphs towards humidity: cloudiness more than normal (i.e. humid), dew point still less than normal (i.e. arid), and daily temperature range still wider than normal (i.e. arid).

Note:

Fully smoothed data – Gaussian smoothing with half-width 6 months – are plotted in red, partly smoothed data uncoloured, and raw data for the last data point in orange. January data points are marked by squares.
Blue diamonds and the dashed blue rectangle show the extreme values in the fully smoothed data record since September 1999.

Normal values are based on averages for the decade from March 1999.* They appear on these graphs as a turquoise (turquoise) circle at the origin (0,0). A range of anomalies called “normal” is shown by a dashed rectangle in aqua (aqua). For values in degrees, the assigned normal range is +/-0.7°; for cloudiness, +/-7%; for monthly rainfall, +/-14 mm.

 * Normal values for rainfall are based on averages for the 125 years beginning 1883.

Relations Among Rainfall Moments

Posted in Australian Climate, Climate Change, Rainfall from 1883 by

Six graphs of rainfall moment relations

Twelve-monthly values of rainfall since 1883 at Manilla NSW yield the four moments of their frequency distributions: mean, variance, skewness, and kurtosis. I plotted the history of each moment (when smoothed) in an earlier post.
Here, I compare the moments in pairs. Connected scatterplots reveal the trajectory of each relationship with time.
Some linear and cyclic trends persist through decades, but none persists through the whole record.
The first image is an index to the suite of six graphs of pair-wise relationships that I present below.

Rainfall variance vs. mean

Trajectory of Variance versus Mean

Continue reading →

Rainfall kurtosis vs. HadCRUT4, revised

Posted in Climate Change, Rainfall from 1883, World Climate by

Patterns of rainfall kurtosis and global temperature.

The kurtosis of annual rainfall at Manilla NSW forms a time-series that matches the time-series of global surface temperature when detrended.

[REVISED:
Earlier posts were based on rainfall data sets that were too small. Estimates of kurtosis and skewness were unstable. For details please read “Rainfall kurtosis matches HadCRUT4” and “Rainfall kurtosis vs. HadCRUT4: scatterplots”.]

The variables

These two climate variables have little in common. Manilla, NSW, is a single station that has a 134-year record of daily rainfall only. That yields estimates of rainfall kurtosis, an indicator of the relative frequency of extreme values.
HadCRUT4 is one of several century-long estimates of near-surface temperature for the whole world. [See Note below: “Data Sources”.]

The visual match of the patterns

The first graph (a dual-axis line chart) shows that these two variables have similar patterns of variation over time.

I found the best visual match by:
* scaling 0.5 units of Manilla rainfall kurtosis to 0.1° of detrended HadCRUT4 temperature;
* aligning the kurtosis value of -0.3 units with the zero of detrended temperature;
* lagging the rainfall by two years.

Features that the two patterns have in common are:
* matching main peaks at 1897, 1942 and 2005, each higher than the one before;
* persistent low values in the 1910’s, 1920’s, 1950’s, 1960’s, 1970’s and early 1980’s;
*some matching minor peaks and troughs.

Regression rainfall kurtosis on HadCRUT4.

The correlation chart

The second graph is a correlation chart. The linear regression of kurtosis on detrended temperature has the reasonable R-squared value of 0.67.
As I have made it a connected scatterplot, you can see how the relation has changed through time. From the first data point in 1898 (in red) both variables decreased together to the lowest temperature in 1910. Both peaked in 1942, having risen since 1920, later falling until 1955-56. The final rise to the highest peak (2005) was continuous from 1984 for temperature, but the rise in kurtosis was not. It fell slightly in 1990, then remained static until 1998.
All rainfall figures actually came two years earlier. [See note below: “Manilla’s 2-year lead”.] The assigned two-year lag not only makes peaks match on the first graph. It sharpens the reversals on the second graph. On a trial connected scatterplot without lag, these reversals had been smooth clockwise curves.

What it means

As evidence of extreme behaviour in climate

It is said that more extremes in climate will occur as the world becomes warmer. The evidence is not strong. Most data sets are overwhelmed by noise, and “extreme” is seldom defined with rigor.
In the present case, I believe that the definition of “extreme” that I use is sound: that is, the kurtosis of a frequency-distribution. The instability of kurtosis when based on my small samples had been an issue. In this revision I have increased the sample population size from 21 to 125.

My rainfall data set that displays more and less extreme behaviour is not general but local. It can merely suggest that data elsewhere may reveal functional relationships.

De-trended global temperature

Continue reading →

Moments of Manilla’s 12-monthly Rainfall

Posted in Australian Climate, Climate Change, Manilla NSW, Rainfall from 1883 by

Manilla 12-monthly rainfall history: Four moments

REVISED, WITH MORE PRECISE DATA
Supersedes the post “Moments of Manilla’s Annual Rainfall Frequency” (15 November 2017). This post includes twelve times as much data.[See Note below: “Data handling”]

Comparing all four moments of the frequency-distributions

Yearly rainfall for Manilla, NSW, has varied widely from decade to decade, but it is not only the mean amounts that have varied. Three other measures have varied, all in different ways.

I based the graph on 125-month (decadal) sub-populations of the 134-year record. I plotted data for every month, at the middle month of each sub-population.
I analysed each sub-population as a frequency-distribution, to give values of the four moments: mean (drawn in indigo), variance (drawn in orange), skewness (drawn in green) and kurtosis (drawn in blue).

[For more about the moments of frequency-distributions, see the post: “Kurtosis, Fat Tails, and Extremes”.]

Each trace of a moment measure seems to have a pattern: they are not like random “noise”. Yet each trace is quite unlike the others.

Twenty-first century values are on the right. They are remarkable in three of the four moments. First, the mean rainfall (indigo) stays near the long-term mean, which has seldom happened before. By contrast, two moments are now near historical extremes: variance (orange) is very low and kurtosis (blue) very positive. Skewness (green) is rather negative.

To my knowledge, such a result has not been observed or predicted, or even suspected, anywhere.

[Note. The main difference from the earlier 4-moment graph based on more sparse data is that skewness does not trend downward.]

Manilla 12-monthly rainfall history: Mean

The mean 12-monthly rainfall (the first moment)

The first moment of the frequency-distribution of 12-monthly rainfall is the mean, or average. It measures of the amount of rain.

As I have shown before, the rainfall was low in the first half of the 20th century, and high in the 1890’s, 1950’s and 1970’s. Rainfall crashed in 1900 and again in 1980.

Manilla 12-monthly rainfall history: Variance

12-monthly rainfall variance (the second moment)

Continue reading →

April 2018 very warm and sunny

Posted in Manilla NSW, Monthly weather by
Gum tree

Schoolyard Lemon-scented Gum

Warm spells several degrees above normal persisted until late in the month. Then normal temperature returned.
While no day went over 35°, thirteen days went over 30°, which was a record. ANZAC Day, at 27.3°, was 3° warmer than usual. That was much the same as last year, but not nearly as warm as in 2002 (28.7°).
A record 25 nights were warmer than 10°. There were no frosts, the coldest night (the 29th) being 5.2°.
There were only three rain days, with the highest reading of 10.2 mm on the 20th. The number of cloudless mornings (16) was a new record, beating April 2001 (15).

Weather log for April 2018

Comparing April months

As in March, so in April, this very warm dry month matched the same month in 2016. The three highest mean temperatures for April months were: in 2018, 20.7°; in 2005, 20.6°; and in 2016, 20.5°. For mean daily maximum temperatures, however, 2005 was the warmest, at 29.5°. April 2018 claims the record highest mean minimum temperature of 12.5°, beating April 2014, which had 12.2°.
The rainfall total of 17.8 mm was at the 31st percentile, well below the average (40 mm). In 2018, rainfall has been below normal in January, March and April. However, serious rainfall shortages below the 10th percentile are still seen only in the medium term: the 60-month total of 2780 mm is at the 8th percentile, and the 72-month total of 3370 mm is at the 6th percentile.

Climate in April months

Data. A Bureau of Meteorology automatic rain gauge operates in the museum yard. From 17 March 2017, 9 am daily readings are published as Manilla Museum, Station 55312.  These reports use that rainfall data when it is available.  The gauge, which had last reported on 24 September 2017, came on line again on the 16th of March.

All data, including subsoil at 750 mm, are from 3 Monash Street, Manilla.