Lights from the night sky as tracers of high altitude weather and climate
The Stormy Sun and the Northern Lights
February 17th 2016
Margit Dyrland
PhD (formerly at UNIS)
Structure and dynamics of the atmosphere
Middle atmosphere2. Stratosphere- 12-50 km- Nacreous clouds, ozone layer- The increase of ozone incr. of temp.- Stratopause – boundary to mesosphere
has temperature ~0°C
3. Mesosphere- 50-90 km- Decrease of temperature to minimum
of ~-100°C at the Mesopause (80-90 km).- Region of meteor ablation, noctilucent
clouds, pmse, airglow- Region of gravity and planetary wave
dissipation- High-energy particle precipitation
Upper atmosphere4. Thermosphere- 90-500 km- Particle precipitation area- Aurora Borealis/Australis- Ionized part of the atmosphere- “Temperature” increase because of lower
density
5. Exosphere- > 500-1000 km- Extremely low pressure vacuum
Lower atmosphere1. Troposphere- 0 to 7-15 km- Most weather phenomena (?)- Formation of gravity & planetary waves- Continuous decrease of temperature- Tropopause – boundary to stratosphere
has temperature ~-60°C
Windows Explorer (2).lnk
ionosphere – occurring
progressively lower down
fridge effect - cooling
greenhouse effect - warming
Upper atmosphere
contracting – satellites
get different drag, effect
on radio signals, gps
etc.
middle atmosphere
(”mesosphere”):
contraction
lower atmosphere:
expansion
time
heig
ht
15km
90km
Climate change
- What happens in the upper atmospheric layers?
Illustration by courtesy of Chris Hall, UiT
The middle atmospheric physics group at UNIS’ main research focus: The mesopause region (80-100 km)
”Courtesy of Michael Wößner”
Today’s lecturetopics:
AirglowMeteorsGravity wavesNoctilucent clouds
http://vimeo.com/42909676
Airglow (Nightglow)
Amazing timelapse video made from photos from ISS by PhD in neuroscience(!) Alex Rivest (www.alexrivest.com):
Airglow
Red and green aurora
Chicago
More about airglow
NASA/ISS-6
Oxygen airglow photographed above Nebraska,
USA (Doug Zubenel)
Oxygen airglow
EUV radiation excites oxygen and nitrogen atoms and molecules in the thermosphere during the day.
The energetic products collide and interact with other atmospheric components, to eventually produce light emission by chemiluminescence and decay of excited atoms and molecules.
Airglow is produced during the day (Dayglow) and night (Nightglow) ALL OVER THE GLOBE, not only in the Polar regions!
Airglow: light emitted by a planetary atmosphere. A glow that surrounds the Earth, not visible to the nakedeye, but can be observed from satellites because theysee it from the side, and thus see a thicker part of it. Also visible to very sensitive cameras at the ground.
Mesospheric airglow layers
Courtesy of Dr. Steven Smith
OH (hydroxyl) airglow (87 km)
Oxygen airglow (97 km)
A narrow layer (8 km thick) centered at ~87 km.
The reason the OH airglow layer is narrow - is that OH is limited at higher altitudes by the
rapid fall off in ozone (O3) concentration with height and at lower levels by the onset of
rapid quenching of the excited products by collisions more frequent at the higher
atmospheric pressures.
The balance between the two limiting processes creates the narrow OH airglow layer.
Sodium airglow (90 km)
Oxygen airglow (94 km)
From KHO we mainly study the airglow from OH:
Dept. of Physics and Astronomy, Georgia
State University
The light spectrum of airglow
Main mechanism for hydroxyl/OH airglow:
H + O3 O2 + OH*(v≤9) + 3.3eV
Vibrationally and
rotationally excited
OH-molecules emit
red and near-infra-red
light .
Nightsky spectrum – between 1200-9000 Å (120-900 nm), recorded by GLO during the flight of STS-
53, December 1992 (Ultaviolet Spectroscopy and Imaging Group, Univ. of Arizona)
“The Silver Bullet” measuring hydroxyl airglow
OH(6-2)
The relative intensities of the different lines give the temperature of the atmosphere at ~87 km
Airglow spectrummeasured at KHO
Different rotational lines
Auroral line 8446Å
“auroral contamination”
Transmitting grating= art at UNIS
Airglow temperatures from Svalbard
Yearly averaged OH(6-2) temperatures:
One of the longest timeseries in the world.
Result: +0.5 ± 0.6 K/year
No negative trend can be detected in the airglow temperatures
Figure: S.E. Holmen, JGR, 2014
Meteors and how we can use them to know the weather and climate in the upper atmosphere
Temperature =
constant∙√(pressure/t1/2)
+ Winds from time delay of
signals between the receivers
Nippon/Norway Svalbard Meteor Radar (NSMR) detects ~6000 meteors every day!
Temperatures at 90 km measured by meteor radar over
Svalbard (green) and from satellite (red)
Note: Cold in the summer and warm in the winter! (opposite to how it is on the ground)
Shows a negative temperature trend of -0.4 ± 0.2K /year
- GWs are created at lower levels of the atmosphere, e.g. when wind blows over mountains, by thunder and storm systems, gradients between ocean and land, etc.
- Gravity waves (GWs) play an essential role in determining the global circulation and thermal balance of the atmosphere.
Gravity waves (also-known as buoyancy waves)
They connect the lower and upper atmosphere – and the northern and southern hemisphere!
Illustration @UCAR, by Alison Rockwell, NCAR Earth Observing
Laboratory.)
Interhemispheric coupling (north-south)
- GWs interact with the winds at the different altitudes and accelerates or decelerates them.
- Wind changes induce temperature changes, and vice versa..
- Drives a wind system from the summer hemisphere to the winter at mesopauselevel Air rises and cools over the summer pole, and descends and warms over the winter pole
Result: Winter mesopause region is warm, summer mesopause region is
cold.
KeoSentry4ix airglow imager. (1) Mamiya RB67 fish-eye lens, (2) collimator lens, (3)
filter wheel, (4) Smart motor system, (5) relay optics, and (6) CCD detector.
OH airglow imager used for gravity wave studies
The KeoSentry4ix imager is designed to image near-infrared emissions from the OH(6-2) band of airglow, same as the spectrometer!
GW properties can be measured from OH airglow images since they lift the layer up/down cooler/warmer temperatures lower/higherintensity
Waves in OH airglow
Time lapse of OH airglow (and aurora) from 19 January 2012
From projected images we can find thecharacteristics of the waves observed. Typical wavelength 20 km, period 10 minutes, speed 15 m/s, direction north-west.
Important information for weather- and climate modelers!
Noctilucent clouds (NLC)
“aka” Polar Mesospheric Clouds - PMC
NLC can be seen from 40-70°N/S (commonly 55-65°)
(f.ex. Oslo)
in July and August
When temperatures are lower than -123°C they form at 80-
85km altitude (in the cold summer mesopause region).
Consist of very small ice particles, with dust as
condensation nuclei (from meteors, volcanoes etc).
Time-lapse of NLC and aurora!
https://www.youtube.com/watch?v=E7
PQbfnErEw
PMC observed from the AIM satellite
NLC over Oslo 24 July 2015 (1 AM)
(Photo: M. Dyrland)
PMC observed from the International Space Station (ISS)
Photo: NASA/ISS028-E-020276
Noctilucent clouds in the Southern Hemisphere are dimmer, less frequent and higher than those in the Northern Hemisphere
NLC/PMC and Polar Mesospheric Summer Echoes (PMSE)
PMSE observed by the EISCAT radar in June 2006
Can be observed by theSOUSY radar in Adventdalen(at the foot of the Mine 7–mountain) and EISCAT
Observed over Svalbard from late May through august
PMSE related to charged dust in the mesosphere
So although we can’t see the noctilucent clouds from the ground, we can still see them with the radar.
Noctilucent clouds and climate
http://www.skyandtelescope.com/about/pressreleases/3308421.html?page=1&c=y
- “First” observation in 1884 after the Krakatoa eruption in 1883.. (Leslie, 1884)
- Increasing numbers of NLC (Gadsden, 1990)
- NLC at lower latitudes (e.g. Logan, Utah at 42°N,
Taylor et al., 2002)
- NLC brightness increase (Deland et al., 2007)
- NLC statistics used as indicator of temperatureand dynamics (Karlsson, 2007)
Number of nights per year with NLC sighting (from Gadsden, 1990)
Noctilucent clouds - NLC
Tutorial video:
http://www.youtube.com/watch?v=-xF2vSKINK0
Photo: Anders M. Lindseth
Hjorthfjellet 27th of December 2015
Red sky 14. Jan 2014
Photo: Anders M. Lindseth
The polar night red skies – The red sky enigma
Allsky camera at KHO 17 Jan 2014
From paper: Sigernes, F., Lloyd, N., Lorentzen, D. A., Neuber, R., Hoppe, U.-P., Degenstein, D., Shumilov, N.,
Moen, J., Gjessing, Y., Havnes, O., Skartveit, A., Raustein, E., Ørbæk, J. B., and Deehr, C. S.: The red-sky enigma
over Svalbard in December 2002, Ann. Geophys., 23, 1593-1602, doi:10.5194/angeo-23-1593-2005, 2005.
«First» observedin 2002. Rare events.
Theory:
Light scatterednorthward by polar stratosphericclouds (PSC)
PSC above Longyearbyen 22.
February 2011
Polar stratospheric clouds (PSC) aka Nacreous clouds aka Mother of pearl clouds
• Two types: PSC I (water, nitric acid, sulphuric acid) and PSC II (water ice only)
• Form when T<-78°C at ~20 km altitude (PSC II at -88°C)
• Visible because they reflect sunlight.
• PSC II probably responsible for the “polar night red skies” since they are so rare
(Photos: M. Dyrland)
PSC above Asker, Norway January 20th 2008.
Photo: Mathias M.
PSC to PSC scattering
Sigernes et al., 2005
Most likely scatteringmechanism. One PSC wouldnot scatter the light far enough north.
All wavelengths smaller than650 nm suffer considerablelosses along the trajectorydue to Rayleigh extinctionand ozone absorption (Lloyd et al., 2005).
Model of the scattering:
N. D. Lloyd, D. A. Degenstein, F. Sigernes, E. J. Llewellyn, D. A.
Lorentzen. The red sky enigma over Svalbard in December
2002: a model using polar stratospheric clouds. Annales
Geophysicae, European Geosciences Union, 2005, 23 (5),
pp.1603-1610
Stratospheric temperature data 6. december 2002
Sigernes et
al., 2005
Stratospheric temperature data 2015-2016
Temperature limit
for PSC formation
http://www.cpc.ncep.noaa.gov/products/stratosphere/temperature/
Zonal average indicate that temperatures were lowenough for PMC in Dec-Jan.
Summary
The atmosphere is a very dynamic system where a lot of processes interact to form Earth’s “weather”.
The stratosphere and mesosphere constitutes the so-called middle atmosphere. The temperature increased in the stratosphere due to ozone absorption of uv radiation. In the mesosphere the temperature decreases to a minimum at the mesopause.
The stratosphere and mesosphere is expected to cool as the troposphere warms.
Airglow, noctilucent clouds and meteors are phenomena in the coldest part of our atmosphere, the mesopause region at 80-100 km. • Airglow is produced all over the globe, all year by extreme uv radiation from the Sun
exciting (“warming”) atmospheric molecules and atoms (e.g. OH, O2, O, Na).
• Noctilucent clouds form when mesospheric temperatures are lower than approx. -120°C, which can happen during the summertime (June-August). They consist of ice condensing on dust (from meteors). Their number has increased the last years.
• From radar measurements of meteors, the temperature and winds in the mesopauseregion can be measured.
When it is very cold in the stratosphere (<-78°C), polar stratospheric clouds can form. The ice clouds can scatter sunlight north to Svalbard, creating “dark season red skies” in mid winter. A rare event that happened for the “first” time in 2002, and again in 2014 and 2016.