Richard, NIWA provides measurements which show New Zealand’s seasonal variation of atmospheric Ozone, and that chart also shows what I think are the latest weekly or daily measurements. Please explain why weekly or daily Ozone measurements sometimes vary as much as the seasonal variation. This might be explained by variations of weekly or daily levels of chemical pollutants, dust, and solar radiation in the stratosphere. However, NIWA’s charts for 5 stations in NZ where UV is measured give daily predictions of UVI and these show almost unchanged predictions from one week to the next? This seems inconsistent with the other chart.
Thanks for tour interest. You’ve obviously been watching these things carefully. Yes, as I mentioned in the post, day-to-day differences in ozone can be +/-10% (or sometimes even larger). This is due to winds in the stratosphere that bring air from higher and lower latitudes, just like the familiar weather patterns in the lower atmosphere. In fact, they’re highly correlated. High pressure systems (anticyclones) are clearly associated with lower ozone amounts because the higher pressures below squeeze ozone-rich air into the lower pressure areas. The calculations in the daily plots are based on the ozone for that day. Near the solstice there’s not much variation in UVI from day to day. Differences are larger near the equinoxes, but that’s mainly because of the rapidly changing noon solar elevations in those seasons. The day-to-day ozone changes cause changes in UVI of a similar magnitude - around 10%). Such differences are hard to detect by just eyeballing a few plots. But if you compare plots from a week or two apart, you can usually see the mean seasonal pattern emerging.
Richard, thanks for your prompt reply. According to DU plots on the seasonal chart, ozone concentrations increased approximately 22% for one week earlier this month. During the same period, daily predictions of UVI for a cloudless sky showed no significant change and that would be less than 10% change if I tried a more accurate estimate. Are UVI predictions based on an aggregate of the previous week of DU measurements?
It has been quite variable this winter, so day-to-day UVI effects should have been visible. But I also see that the satellite ozone data aren’t up to date on the plot.
If ozone data aren’t available at the time the UVI plots are generated, the program that generates them reverts to using climatological mean values. I’m checking with colleagues to see if that’s what’s happening here.
In any case, for UVI forecasts, I recommend that you use the smartphone apps (GlobalUV, or UVNZ if you’re in NZ) rather than the NIWA website.
Richard- This is so useful and informative. I particularly appreciate the graph you shared. Hope you're well this week. Cheers, -Thalia
Richard, NIWA provides measurements which show New Zealand’s seasonal variation of atmospheric Ozone, and that chart also shows what I think are the latest weekly or daily measurements. Please explain why weekly or daily Ozone measurements sometimes vary as much as the seasonal variation. This might be explained by variations of weekly or daily levels of chemical pollutants, dust, and solar radiation in the stratosphere. However, NIWA’s charts for 5 stations in NZ where UV is measured give daily predictions of UVI and these show almost unchanged predictions from one week to the next? This seems inconsistent with the other chart.
Hi Michael
Thanks for tour interest. You’ve obviously been watching these things carefully. Yes, as I mentioned in the post, day-to-day differences in ozone can be +/-10% (or sometimes even larger). This is due to winds in the stratosphere that bring air from higher and lower latitudes, just like the familiar weather patterns in the lower atmosphere. In fact, they’re highly correlated. High pressure systems (anticyclones) are clearly associated with lower ozone amounts because the higher pressures below squeeze ozone-rich air into the lower pressure areas. The calculations in the daily plots are based on the ozone for that day. Near the solstice there’s not much variation in UVI from day to day. Differences are larger near the equinoxes, but that’s mainly because of the rapidly changing noon solar elevations in those seasons. The day-to-day ozone changes cause changes in UVI of a similar magnitude - around 10%). Such differences are hard to detect by just eyeballing a few plots. But if you compare plots from a week or two apart, you can usually see the mean seasonal pattern emerging.
Richard, thanks for your prompt reply. According to DU plots on the seasonal chart, ozone concentrations increased approximately 22% for one week earlier this month. During the same period, daily predictions of UVI for a cloudless sky showed no significant change and that would be less than 10% change if I tried a more accurate estimate. Are UVI predictions based on an aggregate of the previous week of DU measurements?
I see now what you mean with the ozone as plotted in the niwa web site.
https://niwa.co.nz/atmosphere/uv-and-ozone
It has been quite variable this winter, so day-to-day UVI effects should have been visible. But I also see that the satellite ozone data aren’t up to date on the plot.
If ozone data aren’t available at the time the UVI plots are generated, the program that generates them reverts to using climatological mean values. I’m checking with colleagues to see if that’s what’s happening here.
In any case, for UVI forecasts, I recommend that you use the smartphone apps (GlobalUV, or UVNZ if you’re in NZ) rather than the NIWA website.