Optical measurements from three selected wavelengths have been combined with modelling of emissions from an auroral event to estimate the magnitude and direction of small-scale electric fields on either side of an auroral arc. The temporal resolution of the estimates is 0.1 seconds, which is much higher resolution than measurements from SuperDARN from the same region, with which we compare our estimates. Additionally, we have used the SCANDI instrument to measure the neutral wind during the event in order to calculate the height integrated Joule heating. Joule heating obtained from the small scale electric fields gives larger values (17 {plus minus} 11 and 6 {plus minus} 9 mWm-2 on average on each side of the arc) than the Joule heating obtained from more conventionally used SuperDARN data (4.8 mWm-2). This result indicates that high spatial and temporal resolution electric fields may play an important role in the dynamics of the thermosphere, and thus the ionosphere-magnetosphere system in general.