So, to answer Joe's question, the reason for this fix is that the mtclim code uses units of J/m2 instead of W/m2 for its solar radiation, i.e. it deals with total amounts of energy over whatever time interval, rather than the average flux over the interval.  I'd think the best way to fix this would be to change the units of user-supplied SW in initialize_atmos before sending it to MTCLIM, so that MTCLIM requires no change.