1. SP-UK-TRISTATIC Meso-scale ion-neutral coupling
Anasuya Aruliah
SP-UK-TRISTATIC
Unique tristatic measurements of ion-neutral coupling in a common volume using FPIs and EISCAT
The experiment SP-UK-TRISTATIC is the first to measure the ionosphere and thermosphere independently using the 3 EISCAT mainland radars and 3 Fabry-Perot Interferometers to study meso-scale ion-neutral interactions. A common volume at an altitude of 240km is observed and true tristatic measurements of the ion and neutral wind vectors are possible. There is no other such experimental configuration in the world. Other radars use beam-swinging and the assumption of a uniform ion velocity to derive velocity vectors.

2. Thermosphere Preconditions the Ionosphere
Anasuya Aruliah
F-region Neutral Wind Dynamo is 50% of the Magnetospheric Dynamo
SP-UK-Tristatic experiment
Common volume observed by EISCAT (ionosphere) and 3 FPIs (thermosphere)
x- and y-components of magnetospheric (1min and 15min averages) and neutral wind dynamo electric fields Ex
It has long been assumed that the neutral wind dynamo is negligible at high-latitudes where the magnetospheric dynamo is dominant. The experiment SP-UK-Tristatic has shown that the neutral winds in the F-region are on average 50% of the ion velocities, and consequently the neutral wind dynamo should not be ignored.
The experiment has also been the first to demonstrate that Joule heating is due to rapid plasma variations. This has been achieved by comparing the calculation of Joule heating using 1-min and 15-min plasma velocities with ion and neutral temperature variations in the common volume. The EISCAT radar is the only radar in the Scandinavian sector that is capable of such high-time resolution and of measuring Ti and Ne which are necessary for this experiment. Current electric field models use 1-2 hour averages and as a consequence underestimate Joule heating by a factor of two. Further issues of molecular composition that are important to this analysis can also be addressed by EISCAT alone. Ey
First evidence that rapid variation of ion velocities correctly match temperature changes (Ti and Tn) due to Joule heating

3. Thermosphere preconditions the Ionosphere
Anasuya Aruliah
Why is this important? - Geomagnetic history effect
Consequences of thermospheric inertia on magnetosphere-ionosphere coupling
Kp = 1+ (Steady State)
Kp = 1+ (Previously Active)
Dusk side
Dawn side
More energy drawn from the magnetosphere for “previously active” conditions
Why is this important? Inclusion of the neutral wind dynamo changes the amount of energy flux drawn from the magnetosphere. The two plots here are from the Coupled Thermosphere Ionosphere Plasmasphere (CTIP) Global Circulation Model. They show the energy flux into the ionosphere for the same current conditions of date, time and very quiet geomagnetic activity. However, the top plot simulates steady state quiet conditions, while the bottom plot simulates previously active conditions that are currently quiet. The bottom plot shows that the inertia of the thermosphere means that the winds continue to draw energy heavily from the magnetosphere despite the drop to quiet conditions.

4. Thermosphere preconditions the Ionosphere
Anasuya Aruliah
Why is this important? - Geomagnetic history effect
Consequences of thermospheric inertia on magnetosphere-ionosphere coupling
Redistribution of energy into heating and acceleration of the neutral gas
Kp = 1+ (Steady State)
Kp = 1+ (Previously Active)
Dusk side
Dawn side
Most interestingly:
Energy storage → feedback to magnetosphere (negative net flux)
The inertia of the thermosphere also affects how the magnetospheric energy is distributed between resistive heating (Joule heating) and acceleration of the neutral gas. What is particularly interesting is that in certain parts of the polar regions (polar cap and around the Harang Discontinuity) there is a net energy flux out of the ionosphere to the magnetosphere!
The consequences of rapid ion variations being the true representation of Joule heating will significantly modify this theoretical model prediction.

5. Tristatic FPI-EISCAT observations
Anasuya Aruliah
The importance of meso-scale structure: Unique co-located Tristatic Measurements of the Thermosphere (FPIs) and Ionosphere (EISCAT) Aruliah, Griffin, Ford, Aylward, Kosch, Davis
Increase in Ti matches 1-min Joule heating not 15-min averages
Ti < Tn
First evidence that rapid variation of plasma flows correctly matches temperature changes due to Joule heating
Joule heating: 1-min averages vs. 15-min averages
First evidence that rapid variation of plasma flows causes Joule heating
A direct match has been observed between an increase in Ti and Tn with 1 minute average Joule heating but not with 15 min average Joule heating. This should be put in the context of standard global electric field models that use averages over periods up to 2 hours (e.g. Millstone Hill). Meso-scale variations could reconcile the long-known discrepancy of a factor of 2 between model predictions and observations of heating and momentum transfer.
Challenge to assumptions of composition used to calculate Ti
Apparently Ti < Tn, which is energetically impossible since Ni << N_neutrals and therefore the ions will rapidly absorb heat from the surrounding bath of neutrals. Co-located FPI measurements of Tn expose the flaw in the EISCAT radar Ti calculation. This is probably due to incorrect assumptions of the molecular composition of the upper atmosphere at this altitude.
2) Challenge to assumptions of composition used to calculate Ti
Apparent Ti {EISCAT} < observed Tn {FPI}
which is energetically impossible.