CMIT

The Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model is comprised of three models:

Magnetosphere MHD model: LFM
Magnetosphere-Ionosphere Coupler/Solver: MIX
Thermosphere-Ionosphere model: TIEGCM

Shared Variables

The three models that comprise CMIT exchange the following variables at the appropriate boundary conditions:

Variable	Computed by	Sent to
current	LFM	MIX
density	LFM	MIX
soundSpeed	LFM	MIX

Potential	MIX	LFM & TIEGCM
Energy	MIX	TIEGCM
Flux	MIX	TIEGCM

Pedersen Conductance	TIEGCM	MIX
Hall Conductance	TIEGCM	MIX
field-aligned curent	TIEGCM	MIX

Schematic

These three models share data with one another to simulate the Magnetosphere, Ionosphere & Thermosphere. See the flow-chart below for a basic idea of how these models communicate with one another.

Under the hood: CMIT Data Exchange

Nomenclature

Word	Definition
Timestep	The timestep (in seconds) for a parictular model. The models that comprise CMIT operate at different time cadences. The diagram below shows the time exchange rates between the models.
Exchange	Data transfer between models. Can operate in two modes: file exchange or InterComm
File Exchange	(aka adhoc) data is exchanged using file system I/O drop files
InterComm	Data is exchanged over the network. Significantly better performance than file exchange mode
Run	A CMIT simulation over hours, days, weeks. Can be split up into sequences (aka segments)
Sequence	(aka segment) CMIT exchanges over a small period of time (1 to 4 hours). Multiple sequences comprise a CMIT run.

Communication Scheduling Diagram

The following diagram shows

The size of an average time step for each model
The timing in which the models exchange data
The light-blue colored background shows an LFM-MIX sequence (used to precondition the magnetosphere before coupling with the TIEGCM)
The gray colored background shows a fully coupled CMIT sequence.
MIX-TIEGCM exchange
- Three basic operations:
  - MIX sends Flux, Energy & Potential to TIEGCM
  - TIEGCM & MIX time-step
  - TIEGCM sends conductances to MIX
- At the beginning of a sequence, MIX sends to TIEGCM, but doesn't receive data back (since the data is read from a restart file).
- At the end of a sequence, MIX does not send data to TIEGCM, but it receieves data.