Summer Temperatures in South-Central Queensland Part 1: Diurnal Patterns of Temperature Change

In March of this year I purchased from the Bureau of Meteorology one-minute temperature data for the period 1 January to 21 March 2017, for a number of Queensland stations within 250km of Bundaberg.  “One-minute temperature data” is not the temperature of the whole minute, but means temperatures at  of the final second of each minute, so are spot samples taken at regular intervals.  Temperatures can be higher and lower in the intervening seconds, and so for example daily maxima can be several tenths of a degree or more above the final second values, as I demonstrated in earlier posts.

I have analysed data from these stations:  Maryborough, Hervey Bay Airport, Gayndah Airport, Thangool Airport, Bundaberg Airport, Rosslyn Bay, Gladstone Radar, Gladstone Airport, Rundle Island, Nambour, Kingaroy, Tewantin, Maroochydore, Gympie, Double Island Point Lighthouse, and Lady Elliott Island.  Most of these have few missing observations, but all still needed tedious checking.  Kingaroy’s record is atrocious, with days and weeks of intermittent data drop out.

I looked at: one minute temperature change, that is, from one data point to the next; temperature change after 10 minutes; the number of minutes of uninterrupted rise; the number of minutes of uninterrupted fall; and the number of minutes the temperature remained at the same value.

In this post I firstly plot averages of the above metrics across all 16 stations by time of day, to show the range of temperature variation from one minute to the next throughout the day and night, in distinctive diurnal patterns.

Figure 1:  One minute temperature change:-

Mean 1 minute dT

All stations show this distinctive shape, with some variance in range from island to inland stations.

Remember, this plot shows the average of 16 stations every minute of every day for 80 days.

Note the narrow range (averaging less than +/-0.1C) between sunset and sunrise, and the much larger swings from one minute to the next in daylight hours, especially between 09:00 and 15:00.  Outlier points are from weather events at individual stations.

The next plot shows the range of temperature change over 10 minute periods:

Figure 2:  10 minute temperature change:-

Mean 10 minute dT

Note the sharp increase from shortly after sunrise to an early morning peak, then a gradual decrease in the mean to a small dip at around 6 p.m..  Note again the small variation in the absence of the sun, and the many individual weather events shown by outliers.

The next plot counts the number of minutes when the temperature increases each minute at least +0.1C.

Figure 3:  Uninterrupted temperature increase:-

Mean Duration Rising

As you might expect, temperatures rise predominantly during daylight hours, with a sudden jump up just after sunrise, and a dip at sunset.

The next plot counts the number of minutes when the temperature decreases each minute at least -0.1C.

Figure 4:  Uninterrupted temperature decrease:-

Mean Duration Falling

Temperatures generally don’t fall very much just after sunrise.  However note that between 0900 and 1800 it is very rare for the temperature to be falling for zero minutes.  Most long temperature falls occur in daylight hours.  Surprising? What goes up must come down.

The next plot shows the length of time when the temperature does not change from one minute to the next:

Figure 5:  Unchanged temperature:-

Mean Duration Unchanged

Note that during the night on average temperatures are never the same for zero minutes (i.e. they are frequently the same), while in daylight hours temperatures are much less stationary, with a gradual rise from 1500.

The next graphs show the range of these metrics for individual stations.  This will be explored further in a future post.

Figure 6:  One minute temperature change:-

Max min dT comp

This shows the fastest minute to minute temperature change, both up and down.

Figure 7:  10 minute temperature change:-

Max min dT10 comp

Note that there was much faster cooling than warming over 10 minute periods, mostly associated with rain showers, storms, or cool changes.

Figure 8:  Uninterrupted temperature increase:-

Max Duration Rising comp

Figure 9:  Uninterrupted temperature decrease:-

Max Duration Falling comp

Note that Lady Elliott Island (far out to sea) and Rundle Island (in Gladstone Harbour) both had shorter periods of constantly rising and falling temperature.

Figure 10:  Unchanged temperature:-

Max Duration Unchanged comp

On the night of the 6th March at Maroochydore Airport the temperature was 26.1 degrees for 118 minutes.  As you can see nearly all stations had stable temperatures for nearly an hour on at least one occasion.

These results confirm that temperatures in daylight hours are very volatile, while at night temperatures change very little except in unusual weather events.  Fastest and most sustained warming is in the hour after sunrise.  Fastest and most sustained cooling is also in daylight hours.  Night time cooling is much more gradual.  Cooling is on average more rapid than warming.  Rapid warming occurs when the sun suddenly appears.  Rapid cooling is associated with weather events such as rain storms.

In Part 2 (probably not for a week or two) I will look at daily warming and cooling at individual stations.

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2 Responses to “Summer Temperatures in South-Central Queensland Part 1: Diurnal Patterns of Temperature Change”

  1. Geoff Sherrington Says:

    Ken,
    A very interesting analysis you have under way here.
    Small hint – can you give just a few words before each graph to explain why you chose the parameters to plot? Saves the reader having to think of what you have in your mind. Thanks Geoff.

  2. Summer Temperatures in South-Central Queensland Part 2: Weather Events and Spikes | kenskingdom Says:

    […] A Reality Check on Global Warming « Summer Temperatures in South-Central Queensland Part 1: Diurnal Patterns of Temperature Change […]

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