Geoscience Reference
In-Depth Information
DATA
There. are. two. components. to. this. analysis:. (1). regionalization. of. North. American.
precipitation.based.on.correlation.with.global.circulation.modes,.and.(2).evaluation.
of.the.linkages.of.precipitation.climatology.to.the.same.set.of.circulation.modes.for.
a.subset.of.LTER.sites..The.data.used.for.these.two.components.derives.from.three.
sources,.each.of.which.is.discussed.below.
g ridded p reCipiTaTion d aTa
For.the.climate.regionalization.component,.data.from.the.CRU05.data.set.were.used..
This.data.set.was.obtained.from.the.Climate.Research.Unit.of.the.University.of.East.
Anglia.(www.cru.uea.ac.uk/cru/data/hrg.htm)..The.CRU05.data.set.consists.of.grid-
ded.mean.monthly.values.of.nine.climate.variables.for.the.terrestrial.surface.of.the.
Earth.(excluding.Antarctica).for.the.30-year.period.from.1961.to.1990..For.this.anal-
ysis,.only.the.precipitation.data.were.used..The.precipitation.component.of.the.data.
set.was.constructed.from.19,295.global.stations,.interpolated.to.0.5°.×.0.5°.resolution.
using.thin-plate.splines..The.entire.global.database.was.subdivided.into.a.series.of.
geographic. tiles,. then. each. tile. was. interpolated. using. a. separate. spline. function..
Interpolation.accuracy.was.assessed.via.generalized.cross.validation.(GCV),.where.
each.interpolated.value.is.removed.from.the.data.set.and.then.the.summed.square.of.
the.differences.between.the.omitted.point.and.all.other.points.is.calculated.(see.New.
et.al..1999.for.details.of.the.data.set)..The.values.were.also.validated.by.comparison.
to.other.climatologies.
lTer p reCipiTaTion d aTa
Three.criteria.were.used.to.select.sites.for.this.analysis..These.were.(1).located.in.the.
Northern.Hemisphere,.(2).not.primarily.a.marine.site,.and.(3).an.available.climate.
data.series.that.includes.the.time.period.1961-1990..Based.on.these.conditions,.16.
sites.were.chosen.for.analysis.(Figure 9.1,.Table 9.1)..Precipitation.data.were.obtained.
from. the. LTER. CLIMDB. database. (http://www.fsl.orst.edu/climhy/).. Because. the.
LTER.program.was.not.initiated.until.1981,.some.sites.do.not.have.climate.data.sets.
prior.to.this.(some.LTERs.were.established.at.existing.research.sites.with.operating.
climate.stations)..For.these.sites,.observations.from.nearby.recording.stations.were.
used.. Regardless. of. the. actual. location. of. the. observation. sites,. all. measurements.
were. collected. using. methods. consistent. with. US. Weather. Service. observational.
standards..For.precipitation,.this.entails.use.of.the.Weather.Bureau.standard.8-inch.
cylindrical.rain.gauge.
a TmospheriC C irCulaTion m ode d aTa
Four. atmospheric. circulation. modes. were. chosen. for. this. study.. These. are.
described. in. the. following,. along. with. their. data. source.. Together,. these. four.
modes. provide. a. comprehensive. set. of. potential. climate. drivers. for. the. North.
American.LTER.sites.
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