NAME: sm_ns_model PURPOSE: This routine calculates the position along the zaxis at a specific x and y location. The distance to the neutral sheet is the z component of the position data where gsm has been converted to sm, dz2ns=sm[*,2]. CALLING SEQUENCE: zthemis=neutral_sheet(time, position) INPUT: time - string or double format double(s) seconds since 1970 string(s) format: YYYY-MM-DD/hh:mm:ss gsm_pos - position vector in GSM coordinates in re (pos[*,3]) OUTPUT: (default) - displacement of the neutral sheet above or below the XY plane, Re if 'sc2NS' is set - returns distance to the neutral sheet from the S/C position, Re KEYWORDS sc2NS - if set, returns distance from the spacecraft location to the neutral sheet NOTES: For the nominal mission, THEMIS used this model for the inner probes HISTORY:

NAME: themis_NS_model PURPOSE: This routine calculates the position along the zaxis at a specific x and y location. The themis model is used for this calculation. The themis model uses z-sm (converted from z-gsm) for the inner probes and the Hammond model for the outer probes. CALLING SEQUENCE: dz2ns=neutral_sheet(time, position) INPUT: time - string or double format double(s) seconds since 1970 string(s) format: YYYY-MM-DD/hh:mm:ss gsm_pos - position vector in GSM coordinates in re (pos[*,3]) OUTPUT: (default) - displacement of the neutral sheet above or below the XY plane, Re if 'sc2NS' is set - returns distance to the neutral sheet from the S/C position, Re KEYWORDS sc2NS - if set, returns distance from the spacecraft location to the neutral sheet NOTES; Reference: The themis model uses z-sm (converted from z-gsm) for the inner probes and the Hammond model (default) for the outer probes. The algorithm can be found in ssllib neutralsheet.pro. HISTORY:

NAME: aen_ns_model PURPOSE: This program is to find the AEN(Analytical Equatorial Neutral) sheet in the magnetopause in different time and position CALLING SEQUENCE: zaen=neutral_sheet(time, position) INPUT: time - string or double format double(s) seconds since 1970 string(s) format: YYYY-MM-DD/hh:mm:ss gsm_pos - position vector in GSM coordinates in re (pos[*,3] OUTPUT: (default) - displacement of the neutral sheet above or below the XY plane, Re if 'sc2NS' is set - returns distance to the neutral sheet from the S/C position, Re KEYWORDS sc2NS - if set, returns distance from the spacecraft location to the neutral sheet NOTES: References: (1) AEN(Analytical Equatorial Neutral): Zhu, M. and R.-L. Xu, 1994, A continuous neutral sheet model and a normal curved coordinate system in the magnetotail, Chinese J. Space Science, 14, (4)269, (in Chinese). Wang, Z.-D. and R.-L. Xu, Neutral Sheet Observed on ISEE Satellite, Geophysical Research Letter, 21, (19)2087, 1994. (2) Magnetopause model: Sibeck, D. G., R. E. Lopez, and E. C. Roelof, Solar wind control of the magnetopause shape, location, and motion, J. Grophys. Res., 96, 5489, 1991 HISTORY:

NAME: den_ns_model PURPOSE: This program finds the DEN(Displaced Equatorial Neutral) sheet inside the magnetopause in different tine and positions. The routine calculates the position along the zaxis at a specific location. CALLING SEQUENCE: dz2ns=neutral_sheet(time, position) INPUT: time - string or double format double(s) seconds since 1970 string(s) format: YYYY-MM-DD/hh:mm:ss gsm_pos - position vector in GSM coordinates in re (pos[*,3]) OUTPUT: (default) - displacement of the neutral sheet above or below the XY plane, Re if 'sc2NS' is set - returns distance to the neutral sheet from the S/C position, Re KEYWORDS sc2NS - if set, returns distance from the spacecraft location to the neutral sheet NOTES: References: (1) DEN(Displaced Equatorial Neutral): Xu, R.-L., A Displaced Equatorial Neutral Sheet Surface Observed on ISEE-2 Satellite, J. Atmospheric and Terrestrial Phys., 58, 1085, 1991 (2) Magnetopause model: Sibeck, D. G., R. E. Lopez, and R. C. Roelof, Solar wind control of the magnetopause shape, location, and motion, J. Grophys. Res., 96, 5489, 1991 Original Authors of the FORTRAN source code: Ronglan XU and Lei LI, Center for Space Sci. and Applied Res., Chinese Academy of Sciences, PO Box 8701, Beijing 100080, China E-mail: XURL@SUN.IHEP.AC.CN, XURL@SUN20.CSSAR.AC.CN This source code was ported from the original FORTRAN source code into IDL The original source code only calculated to 10.05 RE. In this IDL version that restriction was increased to 25. HISTORY:

NAME: fairfield_NS_model PURPOSE: This routine calculates the position along the zaxis at a specific x and y location. The Fairfield model is used to this calculation. CALLING SEQUENCE: zaen=neutral_sheet(time, position, [rmp=rmp], [ie=ie] INPUT: time - string or double format double(s) seconds since 1970 string(s) format: YYYY-MM-DD/hh:mm:ss gsm_pos - position vector in GSM coordinates in re (pos[*,3]) OUTPUT: (default) - displacement of the neutral sheet above or below the XY plane, Re if 'sc2NS' is set - returns distance to the neutral sheet from the S/C position, Re KEYWORDS sc2NS - if set, returns distance from the spacecraft location to the neutral sheet NOTES: Reference: A statistical determination of the shape and position of the geomagnetic neutral sheet, Journal of Geophysical Research, Vol. 85, No A2, pages 775-780, February 1, 1980 Author - D. Fairfield HISTORY:

NAME: den_fairfield_ns_model PURPOSE: This routine calculates the position along the zaxis at a specific x and y location. CALLING SEQUENCE: dz2ns=den_fairfield_ns_model(time, position) INPUT: time - string or double format double(s) seconds since 1970 string(s) format: YYYY-MM-DD/hh:mm:ss gsm_pos - position vector in GSM coordinates in re (pos[*,3] OUTPUT: (default) - displacement of the neutral sheet above or below the XY plane, Re if 'sc2NS' is set - returns distance to the neutral sheet from the S/C position, Re KEYWORDS sc2NS - if set, returns distance from the spacecraft location to the neutral sheet HISTORY:

NAME: lopez_NS_model PURPOSE: This routine calculates the position along the zaxis at a specific x and y location. The Lopez model is used for this calculation. CALLING SEQUENCE: dz2NS=lopez_NS_model(time, position, kp, mlt) INPUT: time - string or double format double(s) seconds since 1970 string(s) format: YYYY-MM-DD/hh:mm:ss gsm_pos - position vector in re, GSM Coordinates (pos[*,3]) kp - kp index value mlt - magnetic local time in degrees (0=midnight) OUTPUT: (default) - displacement of the neutral sheet above or below the XY plane, Re if 'sc2NS' is set - returns distance to the neutral sheet from the S/C position, Re KEYWORDS sc2NS - if set, returns distance from the spacecraft location to the neutral sheet NOTES: Reference: The position of the magnetotail neutral sheet in the near-Earth Region, Geophysical Research Letters, Vol. 17, No 10, pages 1617-1620, 1990 Author - Ramon E. Lopez The lopez model is best used for distances <8.8 RE HISTORY: