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August 28, 2012


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While Rasmus' plot is very good, it can be improved with ggplot2.

Following the

Date[c(FALSE,(diff(Date) < 0))] <-NA

line, remove everything starting with

to the end of the file.

Then add the following

# Data from Dec 03 1987 to Jan 15 are missing.
# At least Dec 1987 should be removed.

Date[nisdc$Year==1987 & nisdc$Month==12]=NA


# Use 5 day centered average like NSIDC does in the images on www.nsidc.org
nisdc$Ext5d=filter(nisdc$Extent,c(0.2, 0.2, 0.2, 0.2, 0.2),sides=2)

#Stuff Date into data.frame

p=qplot(Date,Ext5d,data=nisdc,color=Year,geom=c("line"),group=Year,alpha=I(8/10),main="Sea Ice Extent 1979-2012 by month\n(colored by year with 2012 in black)",ylab="5 day average extent (millions of sq.km)",xlab="Month of year")

pp = p + geom_line(data=subset(nisdc,Year==2012),color="black",size=2,alpha=0.5)

ppp = pp + coord_cartesian(xlim=c(0.01,11.99)) + scale_x_continuous(breaks=seq(1,12,1)) + opts(axis.text.x = theme_text(hjust=2.5))


This yields a plot showing the annual lines in color that starts with blue in the early 80s and changes to red in the last decade

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