Modelling the Thermosphere-Ionosphere Response to Space Weather Effects: the Problem with the Inputs

Alan Aylward, George Millward, Alex Lotinga

Atmospheric Physics Laboratory

University College London

Using Global Circulation Models as a Forecasting Tool:

• First you need to develop a global model of the upper atmosphere• Then you need to drive it by external inputs in a realistic way• If the physics is right it should simulate the “real” atmosphere and any

transmitted effects• From this grew the idea of forecasting - or at least “nowcasting”. Can

you input data from, say, a solar wind monitor and predict the ionospheric response?

• This takes “Space Weather” into the realm of “Space Weather Forecasting” with many of its concomitant conditions

• We enter the world of data assimilation: the inputs define our accuracy

CTIP/CTIM Properties

• 3-dimensional, time-dependent

• Solves equations of momentum, energy and continuity for ions and neutrals

• 80-500km thermosphere, 110-10,000km for the ionosphere and plasmasphere

• Resolution 2 degs latitude, 18 degrees longitude by 1 scale height altitude. 30-60 seconds time resolution

• 3 neutral constituents (O, O2, N2) and 2 ions (H+, O+)

• Wave forcing at the lower boundary(80km)

• Self-consistent dynamo calculations

“Standard” input of magnetosphere-ionosphere coupling

• An empirical model of high-latitude convection gives the polar cap electric field pattern.

• Many exist - Heppner and Maynard, Foster, Weimar, Heelis, Rich and Maynard

• We use magnetospheric inputs based on statistical models of auroral precipitation and electric fields from Tiros and Foster (Fuller-Rowell

1987 and Foster 1986).

• These inputs are linked to a power index based on TIROS/NOAA auroral particle measurements.

Coupled Thermosphere Ionosphere Plasmasphere model (CTIP)

Atmospheric temperature changes due to dynamic Auroral forcing

(i.e., Magnetic Storm)

Global gravity wave propagation

green/red +20K, blue -20K

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April 1997 Storm event

Dusk effect (neutral winds)

TEC enhancement (particle precipitation)

Total Electron Content (TEC) change

Negative phase (neutral gas composition)

But complications continually arise: the response to storms is not simple:

But how realistic are the inputs?

SuperDARNSuper Dual Auroral Radar Network

Northern Hemisphere

Southern Hemisphere

Joule heating from CTIP model runs

Empirical electric fields

Electric field input derived from

SuperDARN

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So what else is needed?

• We can input SUPERDARN fields at 2 minutes resolution

• But there is a precipitation pattern on top of this• Where can we get that from? Getting matched

precipitation and electric field has long beena problem for GCMs

OVATION datasets (http://sd-www.jhuapl.edu/Aurora/ovation/datasets.html)

OVATION model

Predicts location of auroral oval and maps magnetospheric boundaries onto the ionosphere

Uses:

a) DMSP satellite particle data

b) SuperDARN convection patterns

c) All-sky imaging camera

• However even given these we still need a dense network of stations to constrain the empirical inputs

MIRACLE:

Magnetometers, Ionospheric Radars, All-sky Cameras Large Experiment

Combined ASC images from Kilpisjarvi and Muonio showing

an auroral arc, projected at 110km altitude.

Kurihara et al., Annales, 2006

Experience from US studies:

• A supposedly “operational” nowcasting system has been delivered to the US Air Force using GPS inputs assimilated into an ionosphere model

• However this is without a self-consistent thermosphere• Contrast the density of TEC/Ne measurements with those

of neutral atmosphere composition and winds• The northern US continent is well covered but even for

electron density/TEC coverage outside this is poor. • Does this matter??

Global model of Joule heating for moderate conditions (Thayer, 1995)

Including neutral wind dynamo

No neutral wind dynamo Un=0

The Auroral zone inputs are not the only problem

• The equatorial ionosphere is notoriously difficult to model

• Its scale sizes do not match easily with GCMs• It is part of a general problem that there are

aspects of modelling the ionospheric/thermospheric behaviour which can only be solved globally

• …..And you can’t ignore the lower atmosphere

V = E x B (20 - 40 m/s)

Conclusions

• On the whole we know the physics, much as we do with tropospheric meteorology

• The problem with taking this to “nowcasting” and forecasting is with resolution and inputs

• Whereas some data might be available at a high enough resolution (electron densities) it is unlikely we will ever get neutral atmosphere data at the same density

• “Average” and low resolution behaviour we can simulate well already, but “local” forecasts or specific features is not what you should expect from GCMs