External Controls Flashcards
what does it mean by solar variability
how many sunspots present
define sunspot
dark areas on suns surface which are central parts of active regions
more sunspots = higher solar output
what sunspot cycle are we in now
cycle 25
what happened to sunspots in 2008 and 2019
blank sun
no sunspots visible
like 1954 sun
means lower solar radiation output
2020 sunspots
higher actvity from sun which suggest more spots
2014 they though sun had gone to sleeep
do sunspots impact climate change
unclear
during medieval optimum there was warm summers and winters as lots of sunspots
Little Ice age in Maunder minimum = colder winter as less sunspots
what does it mean by orbital forcing
milankovitch cycles
collective effects of changes in earths movements on climate over thousands of years
what are the 3 recognised variations in changes of earths orbit around the sun?
eccentricity roll
obliquity axial tilt
precession wobble
how long does eccentricity take for one cycle
100,000 yrs
how long does obliquity take for one cycle
41,000 yrs
how long does precession take for one cycle
26,000 yrs
describe eccentricity
creates a rounded perfect circle and changes to elliptical circle due to grav forces
not a large impact on amount of insolation recieved in a yr but influneces lengths of seasons
high eccentricity = greater seasonal variation also linked to ice sheet dvelopment
describe obliquity
tilt of earths axis of rotation
varies from 21.5 - 24.5 degrees
influnces solar radiation reaching earth
large tilt - dimishes contrast in insoltaion between low and high latitudes
(low tilt favours ice sheet developemnt due to low SR)
greater seasonal contrast - area towards sun in summer . tilted away in winter - affects high lats most
describe precession
the season during which earths nearest the sun (perihelion) and furthest away (aphrlion) varies.
n. hemis tilted away from sun at aphelion - \
n hemis tilted towards sun at aphelion - / -favours ice sheet development lower sun radiation
EVIDENCE of milankovitch cycles
cyclic deposits in s.spain - hard/soft layer etc
oxygen isotopes - measure size of ice sheet and temp of water
oxygen ratios
16O ligher
17O
18O heavier
where are more 16O found
clouds
older water
lighter and colder more
during interglacial periods not enriched in 180 but 16o returns quickly to oceans to maintain balance
where are more 18O found
evaporation removes 16o leaving heavier 18o behind
during glacial periods oceans enriched in 18o as 16o stored in ice sheets and doesn’t return quickly to ocean
define el nino
irreuglar warming of sea surface temps off peru and ecuador to central pacific
high air pressure in west/ low pressure in east
weakeneds trade winds
define la nina
colder counterpart of el nino in eastern pacific
intense winds
strengthening of norm
ENSO meaning
el nino southern oscillation
atmospheric pressure changes from east to west which influnces temp and rain on globe
