Table 2.

Results of generalized additive model predicting temperature gradient as a function of longitude, latitude, Julian date and hour. The model includes a two-dimensional smooth term for longitude and latitude, a smooth term for Julian date, and a parametric term for hour as a factor.

	parametric term		smooth term
intercept (s.e.)	term	coefficient (s.e.)	term	effective d.f.	F	p-value	adjusted R2
2.10 (0.001)	hour 6	−0.40 (0.002)	s(lon, lat)	29.00	20 841	<0.001	0.50
	hour 12	−3.43 (0.002)	s(Julian date)	9.00	197 352	<0.001
	hour 18	−1.43 (0.002)