Table 3 Summary of characteristics of Venus electrical activity

Rate of bursts

15/h

~ 1/min

~ 18/h

PV E-field bursts [30 s] (Scarf et al. 1987)

Venera 11 bursts 13–17 km

Venus Express bursts (see text)

Rate of pulses (during burst)

~ 0.14/s

~ 0.1–0.7/s

2–20/s

PV E-field pulses (Ho et al. 1990)

Venera 14 descent pulses (> 200 μV/m/Hz^0.5)

Venera 11 descent pulses (unknown threshold)

Duration of burst events

Well-determined: 5–100 s

• Venera 12 surface burst > 8 s, less than 3–6 min

• VEx magnetometer bursts 6 s to > 60 s

• Venera 9 burst 70 s

• PV E-field bursts

Overlaps between bursts on Veneras 11–14 descent do not constrain burst duration

Flash duration

Unclear

• Venera 9 claims ~ 250 ms (long for terrestrial lightning) but instrument response?

• Hansell ground-based detections < 100 ms (but 5-frame running mean bias subtraction reduces sensitivities to flashes > 50 ms, and discards transients > 250 ms altogether)

• Veneras 11–14 pulses 10–60/s, means up to ~ 8–50 ms long

Venus Express, Pioneer Venus ELF signatures longer than “flash” due to propagation delay, so no constraint (see Fig. 5 bottom panel)

Geographic distribution

Global?

• PV OEFD detections mostly mid-latitude (claimed association with highlands specifically was not substantiated by data, but not excluded either

• VEx MAG detections only made near north pole (low altitude required for observation)

• Venera lander detections made at low latitude, but long detection range gives little localization

Source region size

< few hundred kilometers

• Spin modulation of Venera 11 source

• PV, VEx cover ~ 600 km in 60 s

• Hansell flashes cover 3–15 pixels (2.2 arcsec pixels each ~ 600 km across)

Local time distribution

Strongest observed in evening (18–24 h). But few dayside observations

• Strongly indicated by distribution of PV OEFD and VEx MAG bursts

• Statistics of optical detections too poor to provide useful constraints

Evening cooling of cloud-tops drives convection?