Fig 1.
Schematic of hypothesised pollen entrainment into a thunder cloud, rupturing and deposition mechanisms/processes.
After Taylor and Jonsson [13].
Table 1.
Thresholds and variables used in each of the model experiments.
Fig 2.
Time series in whole grass pollen (a) and pollen shells (b–c) from the RH ≥ 80% experiment.
Panel (b) shows results from in-atmosphere only pollen rupturing, whilst panel (c) includes the on-plant mechanical rupturing from Eqs 2–5. Model values in (c) are on second y-axes to the right. s = slope of the linear regression and r = r correlations between modelled and observed pollen (or pollen shells), given in same colours as the legend. Vertical dashed line indicates the time of the storm.
Fig 3.
Time series in (a) 2m relative humidity (b) 2 m temperature and (c) 10 m wind speed at Melbourne Olympic Park, the closest automatic weather station to the pollen observation site.
The vertical dashed line indicates the time of the storm, the horizontal dashed line indicates the 80% RH threshold.
Fig 4.
(a-c) radiosonde observations at Melbourne Airport compared to model predictions for the 21 November 2016 of relative humidity from the surface to 0 hPa in each meteorological model. (d) pollen concentrations in VGPEM1.0 driven by each meteorological model. Dashed lines in (b) and (d) represent the thresholds for rupturing at 80% RH and 1 grain m-3, respectively. The maximum height of modelled pollen differs because CCAM and WRF are output on pressure levels, whilst the ACCESS height is converted to hPa from the 5 km model level.
Fig 5.
Time series with altitude plots of whole grass pollen (a–c), SPPs to log base 10 (d–f), and relative humidity (g–i) in the atmosphere above the pollen counting site in Melbourne.
ACCESSC-CTM is shown in the left hand panels (a,d,g), CCAMC-CTM in the middle panels (b,e,h) and WRFC-CTM in the right hand panels (c,f,i). Vertical dashed line indicates the time of the storm.
Fig 6.
Time series at Melbourne in (a) dust as PM10, and (b-g) pollen shells for the seven labelled rupturing experiments.
Note the modelled pollen shell concentrations are on the right-hand side y-axes in panels (b-g) and are not similar. s = slope of the linear regression and r = r correlations between modelled and observed pollen shells (or dust), given in same colours as the legend. Vertical dashed line indicates the time of the storm.
Fig 7.
Location of lightning occurrences in 6-hourly blocks starting late 20 November into 21 November 2016.
The pink pixels coincide with timing of the storm passing Melbourne. Basemap from Igismap.com 2020.
Fig 8.
Sub-pollen particles (m-3) in the surface atmosphere at 06:00 UTC.
Does not include mechanical rupturing. The heavy black line shows the approximate position of the storm front diagnosed from radar [19]. Panels (a-c) fWS, (d-f) WS > 5 m s-1 (g-i) RH < 30% and (j-l) lightning. Note the different scale for lightning colourbar. ACCESSC-CTM is shown in the left hand panels (a,d,g,j), CCAMC-CTM in the middle panels (b,e,h,k) and WRFC-CTM in the right hand panels (c,f,I,l). Basemap from Igismap.com 2020.