SGP/EBBR/E4 - Invalid data due to AEM not exchanging

The AEM didn't exchange during the half hour ending 2130 GMT on December 16, 1993.  
This invalidates the half hour values of bowen, e, and h.  We do
not know the biases of the temperature and relative humidity sensors and
thus should not recalculate bowen, e, and h from the 5 and/or 15 minute
data between 2100 and 2130 GMT.

• Surface latent heat flux(latent_heat_flux)
• Bowen ratio(bowen_ratio)
• Surface sensible heat flux(sensible_heat_flux)