This paper presents a descriptive model of substorm-associated east-west electric fields with periods of 30 min in the outer plasmasphere at L?4. The model is based on both published and previously unpublished data on cross-L drifts of whistler paths. The whistler data were acquired on 34 observing days in the years 1963--1975. The recording stations were Eights (L?4), Byrd (L?7), and Siple (L?4), Antarctica. Substorm intervals were defined as those in which the AE index exceeded 200 &ggr;. The rms value of 30-min-average fields on quiet days (AE &ggr;, respectively. The substorm model includes features such as (1) a reversal from eastward to westward fields (outwart to inward drifts) at ~23 MLT, (2) large westward fields on the nightside between 0000 and 0700 MLT mostly in the range 0.2--0.7 mV/m, (3) mostly eastward fields between 0700 and 2400 MLT in the range --0.1 to --0.2 mV/m, and (4) less efficient penetration of substorm electric fields near L=4 near local noon than near dawn or dusk. A number of effects such as spatial structure in outflows near dusk are obscured by the averaging used in the model. There are important differences between temporally isolated and prolonged inward drift events in the postmidnight sector. The primary effect of the former is local modulation of the plasmasphere radius, while the latter tend to be less spatially localized and lead to significant reductions in overall plasmasphere size. Other topics briefly discussed include whistler evidence of relatively large values of the radial (north--south) component of E in the dusk sector, as well as the question of the importance of the component of E induced by fluctuating plasma currents. While the model does not yet account for important temporal and spatial structure in substorm fields, it is believed to include the major spatial features of the east-west field in the outer plasmasphere with periods of 30 min.