a brief introduction to polar cap patchesa brief introduction to a brief introduction to polar cap...

Download A brief introduction to Polar Cap PatchesA brief introduction to A brief introduction to Polar Cap PatchesA

Post on 04-Apr-2020

3 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • A brief introduction to Polar Cap PatchesA brief introduction to Polar Cap Patches by Jøran Moen

    •Chapter 4 from the compendium is essential to understand production, loss, and transport of ionospheric plasma!!

    •Clouds of high electron density form near the cusp inflow region on theClouds of high electron density form near the cusp inflow region on the dayside. They form and enter the polar cap in association with magnetopause reconnection

    Solar EUV ionization is the main production mechanism for high•Solar EUV ionization is the main production mechanism for high density electron patches. When they enter the polar cap they stay in sharp contrast low-density plasma there

    •The patches are frozen into the plasma motion (ExB-drift), and convect with the polar cap twin cell flow from day to night.

    •The patches can be observed by radar and by ground based opticsThe patches can be observed by radar and by ground based optics. Recombination of O+ gives rise to 630.0 and 557.7 nm emissions.

    •The only way for these patches to exit the polar cap is due to tail ti th th th OCBreconnection; then they can cross the OCB.

  • OUTLINE:OUTLINE: • Decay in patch electron

    density and airglowdensity and airglow • 630 nm airglow

    observations in the 18-06 MLT sector

    • Combined all-sky and SuperDARN convectionSuperDARN convection maps

  • Neutralization of O+ and airglow • Key processes:

    ONONO k ++ ++ 1

    OOOO

    ONONO k

    k

    +⎯→⎯+

    +⎯→⎯+ ++

    ++

    22

    2

    2

    1

    ν

    α

    hOO

    OOeO

    +→

    +⎯→⎯++

    *

    * 2

    [ ]+≈ On airglow

    • In the F-region:

    [ ]≈ One

    [ ]+≈ One g

    Neglecting production and transport in the continuity equation we have:

    [ ]O∂ +[ ] l t

    O =

    ∂ ∂ +

    i O+ th l t d it i t ll d b th l t li.e. O+ or the electron density is controlled by the loss term l

  • [ ] [ ] [ ]( )[ ] [ ]

    2221 ++−=

    ∂ ∂ + OkNk

    t O

    O

    [ ] [ ] [ ] [ ] −

    ∂ −=+

    +

    dt

    t

    O

    O β

    β[ ] [ ]

    0

    0

    −=

    +=+

    enn

    e t

    ee

    OO

    β

    β

    Decay of electron density/O+

    where

    [ ] [ ]2221 += OkNkβ 2

    300

    20

    1 100.8 −

    ⎟ ⎠ ⎞⎜

    ⎝ ⎛×=k Teff

    2

    4.0 30017

    2 100.2 − ⎟

    ⎠ ⎞⎜

    ⎝ ⎛×=k Teff

    2329.0 ⊥+= ETT neff

  • Core instrumentation for UiO patch studies:

    LYR NYA

    ARR

  • Polar cap patches: • Major source:

    Solar EUV ionized plasmap

    • Patch definition by density: Ne = 2 x Neo

    • By airglow intensity: Recombination of O+ 50R above 630nm background

    • Horisontal scale 100-1000 km

    • Altitude of Airglow emissions: ~300 km

    TEC image demonstrating transport of EUV ionized plasma that e tends into the polar cap (Foster et al 2005)plasma that extends into the polar cap (Foster et al., 2005)

  • The only way to exit patches from the polar the polar cap is by tailthe polar the polar cap is by tail reconnection

    12 MLT

    70

    80

    0618

    MSP

    24

  • Svalbard – is an ideal platform for studying airglow patches at night

    12 MLT

    High-density patches 70

    High density patches formed in the Canadian/ American cusp sector drift at

    0618

    80

    cusp sector drift at us at night

    MSP

    24

  • Occurence rate of polar cap patches

    Eight winters (1997-2005) of MSP data from Ny-Ålesund have been analyzed

    43 nights, 333 events

    About 60% of the patchesAbout 60% of the patches exit the polar cap from 22-01 MLT, but patches was observed in the entire MLT

    f 18 00 05 00range from 18:00-05:00. 12 MLT

    70

    80

    0618

    24

    MSP

    Moen et al., GRL2008

  • A new tool for studying tail-reconnection dynamics

    Gulbrandsen et al. (Work in progress)

  • NOTE:NOTE: • Patches exit the polar cap in the entire MLT range of

    tail reconnection (18-05 MLT)( ) • All-sky and radar tracking of patches provides a new

    tool to study tail reconnection dynamics. I.e. to observe how thet cross the OCB – the poleward border of the night-time auroral ovalnight-time auroral oval.

    • As high density plasma clouds tend to be turbulent, they are an important space weather phenomenon for communication and navigation systems. See next lidslide.

    • With the ICI-series of sounding rockets, UiO specializes on in-situ measurements of polar cap patches ICI-3 will be launched from Svalbard winterpatches. ICI 3 will be launched from Svalbard winter 2011, and ICI-4 is planned to fly over Svalbard near solar maximum in 2014.

  • Of relevance to satellite navigation

    • Turbulence and irregularities in the ionosphere give rise to scintillations in the satellite to groundgive rise to scintillations in the satellite to ground signal

    • The Total Electron Content (TEC) along the path of a GPS signal can introduce a positioning error ( upa GPS signal can introduce a positioning error ( up to 100 m)

    • More severe in the arctic regions • The effects on GPS can be one of the most• The effects on GPS can be one of the most

    important space weather phenomena for Norway as the Barents sea opens for offshore activities and the East-West passage is likely to open due to

    QuickTime™ and a YUV420 codec decompressor

    are needed to see this picture.

    p g y p sea ice meltdown

  • ICI-2

    Investigation Investigation of Cusp I l i i

    Universitetet i Uppsala i 1983

    Irregularities Universitetet i Uppsala i 1983