Radar was used to observe plasma depletions in the ionosphere known as troughs. Observations showed that troughs have different characteristics between summer and winter. In summer, troughs occur at higher latitudes and show a temperature difference inside and outside the trough with ion upward movement. In winter, troughs occur at lower latitudes without a temperature difference and with ions at rest. The mechanisms that form troughs are different between seasons, with summer troughs forming from ion recombination and winter troughs from a lack of photoionization.

1. RADAR OBSERVATIONS OF PLASMA DEPLETIONS
IN THE IONOSPHERE
INTRODUCTION

The depletions in the F region, known as ionospheric troughs
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Satellite based investigations useful for studying of long-term behaviour or its general properties

Mechanisms that contribute to the formation require other ionospheric parameters data, which can be
provided by the radars

Trough formation attributed to several mechanisms, with plasma convection, neutral wind effects,
precipitation and heating are the most active
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A high ion velocity could result in heating, turn increases the ion loss and leads to a depleted density.
OBSERVATION METHODS
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The Incoherent Scatter (IS) radar is a powerful ground based technique for the study of the Earth's ionosphere

Electromagnetic wave transmitted to ionosphere and high-power energy scattered signal by the electrons in the
ionospheric plasma is detected by large antenna and a sensitive receiver

The frequency spectrum of received signal provides information about the electron density, the electron and ion
temperature, the plasma composition and its velocity, and others

Radar antenna scan the upper atmosphere in north-south plane, covering wide band of latitudes between 60° and 75° N
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Observed at different times of the day, during different seasons
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2. RADAR OBSERVATIONS OF PLASMA DEPLETIONS
IN THE IONOSPHERE
Fig.1 Summer, Evening Hour Fig.2 Winter, Dark Hour Fig.3 Winter, Evening Hour Fig.4 Summer, Night
•
ThroughLatitude Summer higer that winter, night lower than evening, the highest is Fig.1
•
Ion temperature in all cases are increased which caused higher ion loss rate and ion density are decreased, but for
summer there is a temperature differention between inside and outside the trough, for winter not.
•
Ion upward movement for Summer through, and Ion at the rest for Winter through
•
Through formation, summer because of ion recombination, winter because of lacking photo iononization
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3. RADAR OBSERVATIONS OF PLASMA DEPLETIONS
IN THE IONOSPHERE
CONCLUSION
•
Plasma parameters seem to have same characteristics for the same seasons, summer and winter
troughs including location (low latitudes during winter, high latitudes during summer),variation in the
temperatures, the ions behaviour inside and outside the troughs in the similar seasons
•
The plasma parameters behave differently during summer and winter, indicate the fact that formation
mechanisms of the trough are different
•
A more extensive study, including information about the horizontal movement of ions, which required
in order to better understand the formation mechanism of the trough and their prevalence during
certain seasons
REFERENCE

M. Voiculescu, T. Nygren, Radar Observations of Plasma Depletions in the Ionosphere, September
26th 2006.

M. Voiculescu, T. Nygren, Extraterrestrial magnetic field effect on the F region trough, Rom. Journal.
Physic, this issue.
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