VLF measurements of lightning induced electron precipitations and their effects

1
ADVANCING VLF SCIENCE THROUGH THE GLOBAL AWESOME
NETWORK 30-May to 01- Jun 2009, Tunis, Tunisia
VLF measurements of lightning induced electron
precipitations and their effects on the D-region
electron density profile D. ulic1, and V.
Sreckovic1 1 Institute of Physics, University
of Belgrade, Serbia
2
Space weather
The response of our space environment to the
constantly changing Sun is known as space
weather. When the space environment is disturbed
by the variable outputs of the Sun, technologies
that we depend on, both in orbit and on the
ground can be affected. Some of the most
dramatic space weather effects occur in
association with eruptions of material from the
solar atmosphere into interplanetary space.
3
Introduction

• Over the last several decades, the monitoring of
  VLF transmitters has been used to study remote
  and transient perturbations of the lower
  ionosphere associated with lightning discharges.
• Indeed, these phenomena generate typical
  amplitude and phase variations of the
  subionospheric signals, known as the LEP effect.
• The perturbation begins by a rapid change in the
  trans-mission amplitude and/or phase, followed by
  a relatively slow recovery (lt100 s) to the
  original unperturbed signal.

4
Ionosphere
The ionosphere is the region extending from about
60 km to several hundreds km, where the motion of
free electrons have strong effects on medium and
high-frequency radiowave propagation
5
Propagation of VLF waves
6
Belgrade station

• Belgrade (44.85N 20.38E)

• AbsPAL (Absolute Phase Amplitude Logger)
  receiver was installed at the Institute of
  Physics, University of Belgrade, in August 2003.

7
Belgrade station
AWESOME STATION was installed at the Institute
of Physics, Belgrade in June 2008.
8
(No Transcript)
9
List of recorded VLF signals
10
Statistical results

• During period from 2004 to May 2009 were recorded
  5300 of LEP events
• Most of recorded LEP events occurred during local
  summer and autumn, very rare during winter and
  spring
• Large number of LEP events were detected on
  signal GQD/22.1 kHz Belgrade
• Amplitude changed DA lt 1(dB)
• Phase changed few degrees

11
Method of numerical modeling

• This work is concerned with the numerical
  simulations of VLF perturbations. The method is
  based on changing the pair of Waits parameter
  sharpness b in km-1 and reflection height h in
  km, along segments of GCP.
• The aim is to obtain calculated values
• DAcal Anonpert - Apert and Df fnonpert -
  fpert
• to be equal or very close with recorded
  values DArec and Dfrec
• The RANGE EXPONENTIAL model (LWPCv21 program) is
  used to examine a single propagation path. In
  this model a user specifies a range-dependent
  ionospheric variation.

12
Ambient ionospheric condition

• Wait and Spies (1964) defined a convenient
  quantity to describe the characteristics of the
  lower ionosphere as the conductivity parameter wr
  which is
• wr wo2/n 2.5 x105 s-1,
  
• wo the plasma frequency of the electrons, and
  n the electron-neutral collision frequency.
• The ionospheric electron density and collision
  frequency profiles are given by a standard
  nighttime ionospheric model.
• The collision frequency profile is given by

13
Ambient ionospheric condition
- -

• The unperturbed electron density profile given
  by

where the pair of Wait's parameters are
sharpness b in km-1, reflection height h in km.
The height above the Earths surface is h in km .

• Under nighttime conditions, the typical ranges
  for b and h are 0.40 to 0.50 km-1 and 80 to 90
  km, respectively.

14
SOLAR FLARE
The intense radiation from a solar flare travels
to Earth in eight minutes.

• The Earths upper atmosphere becomes more ionized
  and expands.
• Long distance radio signals can be disrupted by
  the resulting change in the Earths ionosphere.
• A satellites orbit around the Earth can be
  disturbed from the expand atmosphere.
• Satellites electronic components can be damaged.

15
Sunspot 798 in September 2005
Hyperactive sunspot 798 unleashed nine X-class
solar flares including a colossal X17-flare
(Sept. 07, 2005)
This colossal spot made September 2005 the most
active month on the Sun in almost 15 years.
16
06 10 September 2005

• In the period 06 10 Sep 2005 more than 50 LEP
  events were recorded each night.
• Most of them were recorded on signals GQD/22.10
  kHz and NAA/24.0kHz.

17
Calculated electron density on height of
reflection over path
18
Location of electron density enhancement
19
CORONAL MASS EJECTION
One of the most important solar events from
Earth's perspective is the coronal mass ejection,
the solar equivalent of a hurricane.
A CME is an eruption of a huge bubble of
energized plasma from the Sun's outer atmosphere,
or corona
Having escaped the Sun's gravity, a CME speeds
across the gulf of space at velocities of some
400 km/s. They reach the Earth in 2.5 to 5 days.
20
December 04/05 2004

• In the night Dec 04/05 (from 17 UT to 06 UT) more
  than 300 LEP events were recorded.
• Most of them on signals GQD/22.10 kHz and
  ICV/20.27kHz.
• Sporadically during that night LEPs were
  recorded on four signals

21
Calculated electron density
22
Location of electron enhancement
LEP events observed simultaneously on the four
VLF paths ware the pointer to the geographical
location of the region of enhancement density,
over Europe.
23
Solar eclipse on October 03, 2005
GQD/22,1 kHz
24
We would like .
25
Summary

• The use of VLF transmissions propagating inside
  the waveguide Earth ionosphere is well
  developed technique for probing conditions
  inside the ionospheric D-region.
• For daytime propagation conditions, the D-region
  is particularly stable, with reflections heights
  occurring at about 70-75 km.
• Additional perturbations are driven by solar
  flares and total solar eclipses. Variations in
  the D-region lead to changes in the propagation
  conditions for VLF waves inside the waveguide.
• LEP events observed simultaneously on the several
  VLF paths can be used as the pointer to the
  geographical location of the region of
  enhancement density, over Europe
• Recorded data at the Belgrade station are used to
  study global and local conditions in the D-region
  in order to make relevant models.