The LTR developer pages contain information & diagrams specific to code development of model coupling.

LFM-Para

LFM-MIX

LFM-MIX is a coupled model between LFM and MIX. MIX provides an inner boundary condition for the LFM global MHD model. LFM computes and MIX solves the potential in the equation

Pseudo-code

Convention:

at time
LFM startup: Read step , , ( if starting from scratch) from file
Loop
1. mhd.Boundary() updates the Solar Wind boundary condition
2. How big of a step do we take on iteration ?
  = mhd.courant()
3. Advance LFM, obtaining new values
  mhd.step, ,
4. Do we exchange with MIX?
  1. Yes?
    1. Send UT time of the current step to MIX
    2. Send , , from LFM to MIX
  2. Solve for potential with MIX
  3. Is this an I/O step for MIX?
    1. Yes? Write to mix_step-i.hdf
    2. MHD Receives
5. Is this an I/O step for LFM?
  1. Yes? Write , , to mhd_step-i.dmp

What is the maximal number of processors I can use for my grid?

There are three constraints to determine the maximum number of processors that should be used for a particular grid:

The LFM uses a 8th-order spatial method in each of the i, j and k directions. Therefore, each processor should have a ''minimum of 8 cells'' in each direction.
The grid is decomposed spatially in terms of XY planes (i.e. in i-j space). The grid is currently not parallelized in the k direction.
The grid decomposition only works for np > 1. Using a single processor (np=1) may give unexpected results.

A formula to determine the number of processors is:

Example 1: 53x24x32

For example, using the default on a 53x24x32 grid, and . So

So you can use up to 18 processors on a 53x24x32 grid.

Example 2: 106x48x64

On a 106x48x64 grid, and . So

So you can use up to 78 processors on a 106x48x64 grid.

LFM-MIX-RCM(-TIEGCM)

Exchange Diagram

This diagram shows the order of data exchanges between LFM, MIX, TIEGCM and RCM. Click for a larger version:

Order of Exchanges

Sequence Type definition

start: Occurs only once, at the beginning of a sequence:
loop, middle: Occurs one or more times within time loop. Prefixed/suffixed by one start & stop exchange.
start: Occurs only once, at the end of a sequence:

Exchange ordering table

Sequence Type	Exchange Order	UT	LFM	MIX	RCM
start	1	4:00:00	Send to MIX	Recv from LFM
start		4:00:00		Compute Potential
start	2	4:00:00	Recv from MIX	Send to LFM
start	3	4:00:00	Send to RCM		Recv from LFM
start	4	4:00:00		Send to RCM	Recv from MIX

loop		4:00:10	Send to MIX	Recv from LFM
loop		4:00:10		Compute Potential
loop		4:00:10	Recv from MIX	Send to LFM
loop	...

middle	1	4:02:00	Recv from RCM		Send to LFM
middle	2	4:02:00	Send to MIX	Recv from LFM
middle	3	4:02:00		Recv from RCM	Send to MIX
middle		4:02:00		Compute Potential
middle	4	4:02:00	Recv from MIX	Send to LFM
middle	5	4:02:00		Send to RCM	Recv from MIX
middle	6	4:02:00	Send to RCM		Recv from LFM

loop		4:02:10	Send to MIX	Recv from LFM
loop		4:02:10		Compute Potential
loop		4:02:10	Recv from MIX	Send to LFM
loop	...

end	1	4:04:00	Recv from RCM		Send to LFM
end	2	4:04:00	Send to MIX	Recv from LFM
end	3	4:04:00		Recv from RCM	Send to MIX
end		4:04:00		Compute Potential
end	4	4:04:00	Recv from MIX	Send to LFM

Inter-model Communication

Shared Variables

Handshake Variables

RCM Intermediate Grid

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units	Notes
1	im-mhd_ig_size	Nx, Ny, Nz	1d array (len=3)	int	n/a	1xN broadcast
2	im-mhd_igx	X	1d array (Nx)	float	m (SM Coord)	1xN broadcast
3	im-mhd_igy	Y	1d array (Ny)	float	m (SM Coord)	1xN broadcast
4	im-mhd_igz	Z	1d array (Nz)	float	m (SM Coord)	1xN broadcast

LFM Grid

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units
5	mhd-im_lfm_size	Ni, Nj, Nk	1d array (len=3)	int	n/a
6	mhd-im_lfmx	X cell center	3d array (Ni+1,Nj+1,Nk+1)	float	m (SM Coord)
7	mhd-im_lfmy	Y cell center	3d array (Ni+1,Nj+1,Nk+1)	float	m (SM Coord)
8	mhd-im_lfmz	Z cell center	3d array (Ni+1,Nj+1,Nk+1)	float	m (SM Coord)

Other

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units	Notes
9	mhd-im_dipole_moment	Dipole Moment	scalar	float	m k s	1xN broadcast

Accumulate Variables (LFM -> RCM)

Click here for a description of the Accumulate routine.

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units
1	mhd-im_density	rho	1-d (NxNyNz) on intermediate grid	float	SI units
2	mhd-im_pressure	P	1-d (NxNyNz) on intermediate grid	float	SI units
3	mhd-im_bx	Bx	1-d (NxNyNz) on intermediate grid	float	SI units
4	mhd-im_by	By	1-d (NxNyNz) on intermediate grid	float	SI units
5	mhd-im_bz	Bz	1-d (NxNyNz) on intermediate grid	float	SI units
6	mhd-im_v	magnitude(v)	1-d (NxNyNz) on intermediate grid	float	SI units

Bleed Variables (RCM -> LFM)

Send Order	IC_Variable	Variable(s)	Dimensions/Size	Type	Units	Notes
1	im-mhd_density	rho	3-d (Ni+1,Nj+1,Nk+1) LFM cell-centered	float	SI units
2	im-mhd_pressure	P	3-d (Ni+1,Nj+1,Nk+1) LFM cell-centered	float	SI units
3	im-mhd_rcm_mask	mask	3-d (Ni+1,Nj+1,Nk+1) LFM cell-centered	int	N/A	0 - not part of RCM 1 - part of RCM

Ionosphere Handhsake

RCM Ionosphere Grid

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units	Notes
1	im-cpl_im_size	nLon, nLat	1-d array (len=2)	int	N/A	nLon+1 brings you back to the periodic point
2	cpl-im_r_i	R_i	scalar	float	m	Radius of Ionosphere; IM exits if its value of RION is different in CPL
3	im-cpl_latitude	latitude	1-d array (nLat)	float	co-latitude from pole (SM, radians)
4	im-cpl_longitude	longitude	1-d array (nLon)	float	0 at noon (SM, radians)

Ionospheric Variables

Important Notes:

RCM only needs one hemisphere of data
MIX: J: Positive is down in the Northern hemisphere
Ionosphere handshake occurs after MHD (LFM) handshake.

RCM Ionosphere information (i.e. sent to LFM/MIX)

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units	Notes
1	im-cpl_avg_energy	E_av (Avg Eng)	2-d (nLat, nLon)	float	J (SI)	Unused by MIX as of r1268 (April 2010)
2	im-cpl_avg_flux	F_e (Energy Flux)	2-d (nLat, nLon)	float	W/(m*m) (SI)	Unused by MIX as of r1268 (April 2010)
3	im-cpl_fac	J (total FAC density)	2-d (nLat, nLon)	float	A/(m*m) (SI)	Unused by MIX as of r1268 (April 2010); How does MIX split the total FAC, which is defined once for half-grid?

LFM/MIX ionosphere information (i.e. sent to RCM)

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units
1	cpl-im_potential	phi (potential	2-d (nLat, nLon) - on RCM grid	float	V (SI)
2	cpl-im_sigma_p	Pedersen Conductance	2-d (nLat, nLon) - on RCM grid	float
3	cpl-im_sigma_h	Hall conductance	2-d (nLat, nLon) - on RCM grid	float

Note: MIX currently sends the Potential and conductances for the Northern hemisphere only! In the future we need to somehow average or sum over both hemispheres.

Time Exchange

All time exchanges occur as a UT floating-point array (Year, Month, Day, Hour, Minute, Second). Note we pack extra information into the array for clean, efficient data transfer between the code.

Handshake

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units	Notes
1	mhd-im_startup_scalars	kill signal, Start UT, delta t (in seconds)	1-d (8 elements)	int	Kill_signal, Y, M, D, H, M, S, dt	1xN broadcast

At each exchange...

Send Order	IC Variable	Variable(s)	Dimensions/Size	Type	Units	Notes
1	mhd-im_scalars	kill signal, current UT	1-d (8 elements)	int	Kill_signal, Y, M, D, H, M, S	1xN broadcast

Kill_signal:

0: OK, keep time stepping.
111: LFM has finished, kill.
222: second-to last exchange.