**Fig. 4.** Seasonal mesospheric *OH* airglow winter temperature trend over Svalbard 1980 - 2001. The daily mean** **temperatures are plotted as
small dots. The
monthly mean temperatures are plotted for December (triangles) and January (circles).
The seasonal averages (filled circles) have the standard deviation plotted as
error bars. The solid line represents the linear trend. The dotted line is the estimated linear trend using weights equal to number of days per season divided by the standard deviation.