Lights from the night sky as tracers of high altitude ... · Lights from the night sky as tracers...

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.