Are there warm spots in Rangiora?

In air quality lingo we normally refer to small areas of increased pollutant concentrations as hot spots but since this story is about the temperature field I needed to use something else ... warm spots will do.

As part of the measurement campaign we deployed in Rangiora we not only used ODINs but also four weather stations (like the one on the picture) scattered around the town to explore small scale wind flows and how uniform or otherwise the temperature field is in the area.



Before we dive too deep in the analysis, let's pause and look at the two kind of temperature sensors used here. First is the meteorological sites that have thoroughly calibrated and well housed thermometers, protected from the sunshine while the ODIN thermometers were ... well ... not perfectly housed (see image of the inside of an ODIN) and then put in plain sunlight attached to lamp posts (see image of ODIN attached to a lamp post).

Now, don't despair! There is a reason why the ODIN temperature sensor was housed like that. It is meant to keep an eye on the temperature near the dust sensor, not necessarily the outdoor temperature but as we will see, the ODIN temperature data compares quite well with the data from the proper meteorological sites... most of the time.

First, the spatial coverage of the temperature sensors in Rangiora. Below you can see, in addition to the sites shown previously (see ODIN results), the meteorological stations setup for this campaign (blue circles) and the permanent weather station (blue triangle).

So, we have a rather good coverage of the urban part of Rangiora and its surroundings so we can tackle the question of how uniform is the temperature field in Rangiora?

Below we can see the daytime (between 08:00 and 18:59) and nighttime (between 19:00 to 07:59) temperature measured around the area (click to enlarge). The first feature that drew our attention was that the temperature measured outside the town was consistently lower than that measured inside. The concept of urban heat island is tempting but the fact that the daytime temperature difference between urban/rural sites is larger than during nighttime indicates that there is something else at play...

Let's explore a little more these data to try to answer the original question. First the easy one, the daytime field. the temperature inside the town seems relatively uniform (most circles have the same colour blue) with temperatures ranging between ~11$C$and ~13$C$ except for the central circle that corresponds to ECan's air quality site and the light blue dot to the north-east of town (ODIN_06) that are around 10$C$.

So, are these two places colder than the rest of the town? Probably not really. The most likely explanation for the observed difference is the location and housing of the sensors. As I indicated above, ECan's temperature sensor is housed in a radiation shield and is properly calibrated. While ODIN's are basically housed in a plastic box in full sun so we expected the temperature measured by the ODIN's to be higher than what a "real" thermometer would measure, which is true for most of the ODINs ... except for ODIN_06. The image below should clarify what's going on with that unit. The box is strapped facing northish to a lamp post very close to a rather large tree that shades the unit for most of the day, explaining the lower temperature compared to the rest of the ODINS and making it closer to that observed by a proper site like ECan's. So ... it seems that, during daytime there aren't warm spots in Rangiora


OK, but that's daytime ... Nighttime is more interesting but the differences are much smaller and the only really significant difference is between the outside and the inside of the town which may hint at a heat island effect but we require more detailed analysis to say anything like that and for the time being our conclusion is:
Rangiora doesn't have warm spots .... but it may have (air pollution) hot spots which we will explore in a future update.