Weimer05FAC, Wing10FAC & Null at Noon

FAC and Auroral Hiss Occurrence Rate:

Above figure shows the integrated, around SP geomagnetic latitude, Ionospheric FAC, taken from the Weimer05 model, for +90 and -90 deg. IMF Clock Angle, showing IMF By dependence, from morning to midnight magnetic local time. It also shows, in red, auroral hiss occurrence  for the said IMF Clock angles.

Notes:
- As IMF By goes from -ve to +ve, we see that FAC in the post-noon sector become more negative / upward FAC increase, and we see a corresponding increase in the auroral hiss occurrence rate.
- We cannot explain from this figure the correlation of pre-midnight and pre-noon hiss on IMF By +ve. This is because upward currents increase in these two time sectors for IMF By -ve and Not for IMF By +ve.

Another important fact to note here about the Weimer 05 model is that, it shows dominating downward currents in the pre-noon sector for IMF By -ve at the South Pole latitude. This is in contrast to what Yan et al. (2012) point out from Wing et al. (2010) that at the South Pole latitude, we expect upward R2 FAC to dominate under the IMF By -ve conditions, as shown below:

First figure is for IMF By>0, which should logically correspond to IMF By<0 in the Southern hemisphere as Doyle et al. (1981) and others suggest about the conjugate FAC patterns.

Null at Noon in the Hiss Occurrence Rate:

I searched up that a list of authors (as discussed below) have shown evidence of and have tried to explain this gap in the occurrence of auroral phenomenon in the Southern Hemisphere:
1. Yan et al. (2012) say that "During a few hours around noon, the station is in the so-called throat
ow from dayside into the polar cap with little energetic electron precipitation."
2. Dandekar et al. (1978) say that "A  gap in the midday sector of the auroral oval is examined on the basis of Defense Meteorological Satellite Program (DMSP)  satellite auroral photographs"
3. Iijima and Potemra (1976) report a "confusion in the direction of the large-scale field-aligned currents
in  the  polar  cusp region around  1130-1230 MLT  during weakly disturbed conditions"
4. McDiarmid et al. (1976) note that electron spectra are harder in the postnoon (1400-1600  MLT)  sector than  in  the prenoon (1000-1200 MLT)  sector
5. Zaitzeva and Pudovkin (1976) show an existence of a midday auroral gap and hence a unique localized region of particle and field phenomena.