Evidence for charged aerosols and associated meter‐scale structure in identified PMSE/NLC regions

Mitchell, John; Croskey, C. L.; Goldberg, R. A.

doi:10.1029/2000gl012685

Cited by 39 publications

(38 citation statements)

References 7 publications

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“…These measurements are however much more difficult to explain than the observations of negatively charged particles. In subsequent campaigns, several investigations have provided further evidence for the existence of negatively charged aerosol particles in PMSE (Havnes et al, 2001;Mitchell et al, 2001Mitchell et al, , 2003Smiley et al, 2003). Concerning positively charged particles there seem to be further indications that they do exist (Mitchell et al, , 2003Smiley et al, 2003), however, our current understanding of these measurements is far from being conclusive.…”

Section: Observation Of Charged Ice Particlesmentioning

confidence: 90%

Polar mesosphere summer echoes (PMSE): Review of observations and current understanding

Rapp¹,

Lübken²

2004

Atmos. Chem. Phys.

363

350

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Abstract. Polar mesosphere summer echoes (PMSE) are very strong radar echoes primarily studied in the VHF wavelength range from altitudes close to the polar summer mesopause. Radar waves are scattered at irregularities in the radar refractive index which at mesopause altitudes is effectively determined by the electron number density. For efficient scatter, the electron number density must reveal structures at the radar half wavelength (Bragg condition for monostatic radars; ∼3 m for typical VHF radars). The question how such small scale electron number density structures are created in the mesopause region has been a longstanding open scientific question for almost 30 years. This paper reviews experimental and theoretical milestones on the way to an advanced understanding of PMSE. Based on new experimental results from in situ observations with sounding rockets, ground based observations with radars and lidars, numerical simulations with microphysical models of the life cycle of mesospheric aerosol particles, and theoretical considerations regarding the diffusivity of electrons in the ice loaded complex plasma of the mesopause region, a consistent explanation for the generation of these radar echoes has been developed. The main idea is that mesospheric neutral air turbulence in combination with a significantly reduced electron diffusivity due to the presence of heavy charged ice aerosol particles (radii ∼5-50 nm) leads to the creation of structures at spatial scales significantly smaller than the inner scale of the neutral gas turbulent velocity field itself. Importantly, owing to their very low diffusivity, the plasma structures acquire a very long lifetime, i.e., 10 min to hours in the presence of particles with radii between 10 and 50 nm. This leads to a temporal decoupling of active neutral air turbulence and the existence of small scale plasma structures and PMSE and thus readily explains observations proving the absence of neutral air turbulence at PMSE altitudes. With this explaCorrespondence to: M. Rapp (rapp@iap-kborn.de) nation at hand, it becomes clear that PMSE are a suitable tool to permanently monitor the thermal and dynamical structure of the mesopause region allowing insights into important atmospheric key parameters like neutral temperatures, winds, gravity wave parameters, turbulence, solar cycle effects, and long term changes.

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Section: Observation Of Charged Ice Particlesmentioning

confidence: 90%

Polar mesosphere summer echoes (PMSE): Review of observations and current understanding

Rapp¹,

Lübken²

2004

Atmos. Chem. Phys.

363

350

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“…The dust was not observed visually or by lidars but a strong PMSE layer was present. Later, rocket probe observations (Mitchell et al, 2001;Havnes et al, 2001a, b;Smiley et al, 2006) confirm the presence, also of subvisual dust, at NLC and PME conditions.…”

Section: Introductionmentioning

confidence: 90%

Mesospheric dust and its secondary effects as observed by the ESPRIT payload

Havnes

Surdal²,

Philbrick

2009

Ann. Geophys.

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Abstract. The dust detector on the ESPRIT rocket detected two extended dust/aerosol layers during the launch on 1 July 2006. The lower layer at height ∼81.5-83 km coincided with a strong NLC and PMSE layer. The maximum dust charge density was ∼−3.5×10 9 e m −3 and the dust layer was characterized by a few strong dust layers where the dust charge density at the upper edges changed by factors 2-3 over a distance of 10 m, while the same change at their lower edges were much more gradual. The upper edge of this layer is also sharp, with a change in the probe current from zero to I DC =−10 −11 A over ∼10 m, while the same change at the low edge occurs over ∼500 m. The second dust layer at ∼85-92 km was in the height range of a comparatively weak PMSE layer and the maximum dust charge density was ∼−10 8 e m −3 . This demonstrates that PMSE can be formed even if the ratio of the dust charge density to the electron density P =N d Z d /n e 0.01.In spite of the dust detector being constructed to reduce possible secondary charging effects from dust impacts, it was found that they were clearly present during the passage through both layers. The measured secondary charging effects confirm recent results that dust in the NLC and PMSE layers can be very effective in producing secondary charges with up to ∼50 to 100 electron charges being rubbed off by one impacting large dust particle, if the impact angle is θ i 20-35 • . This again lends support to the suggested model for NLC and PMSE dust particles (Havnes and Naesheim, 2007) as a loosely bound water-ice clump interspersed with a considerable number of sub-nanometer-sized meteoric smoke particles, possibly also contaminated with meteoric atomic species.

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“…It should be noted here that for a dust material density of about 2 gm cm −3 , the mass of a 1-nm dust particle is about 5000 amu. Mitchell et al (2001) from rocket experiments conducted from Norway, reported the observation of electron bite outs in the height region of 84-86 km, caused by negatively charged aerosol dust.…”

Section: Role Of Charged Dust Particlesmentioning

confidence: 99%

On the height variation of the E-region cowling conductivity – effect of charged dust particles

Muralikrishna

Kulkarni

2006

Ann. Geophys.

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Abstract. Height profiles of the Cowling conductivity in the electrojet region, estimated using the atmospheric parameters given by the existing models like CIRA or MSIS and measured electron density profiles, consistently show the heights of the electrojet current intensity peak to be more than 3 km below those estimated from in-situ measurements using magnetometers on board sounding rockets. Kulkarni and Muralikrishna (2005) attempted to explain this to be due to the effect of neutral dust particles. They reported that neutral dust particles, when they exist in sufficient numbers, can modify the collision parameters, especially in the lower E-region, where dust particles of meteoric origin are known to exist in large numbers, and thereby can modify the Cowling conductivity profile in the electrojet region. This work is extended here to include the effect of charged dust particles. Dust particles can become charged negatively by the attachment of ambient free electrons, and can thus reduce the number density of free electrons especially below the electrojet peak. This can alter the vertical profile of the east-west Hall current driven by the vertical Hall polarization field, thereby causing a net reduction in the electrojet current. Such a decrease in the electrojet current may be observed on the ground magnetograms. This mechanism, as proposed here, can operate only during periods of strong meteor shower activity, when the dust particle density at the assumed deposit height of 103 km can reach extreme values (for example, 5×10 4 cm −3 of 1-µm diameter dust particles). Such a dense dust layer may even cause a reversal in the normally upward vertical Hall polarization field, within the dust layer, causing a reversal of the electrojet currents below the current peak.

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Evidence for charged aerosols and associated meter‐scale structure in identified PMSE/NLC regions

Cited by 39 publications

References 7 publications

Polar mesosphere summer echoes (PMSE): Review of observations and current understanding

Polar mesosphere summer echoes (PMSE): Review of observations and current understanding

Mesospheric dust and its secondary effects as observed by the ESPRIT payload

On the height variation of the E-region cowling conductivity – effect of charged dust particles

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