This is the README file for LAPIPA LAPIPA contains the Dynamics Explorer-2 Precipitation Angle and Pitch Angle (PA) data for the LAPI experiment generated from the LAPI description and the sensor offset angle found in the LAPISEA data set. The LAPI CDF files were generated by converting the VAX binary format stored at the Space Physics Data Facility (SPDF). The VAX binary format was converted from the original Sigma-9 machine that was used to collect and process Dynamics Explorer telemetry. At the time DE-2 was flown, data from the science magnetometer (MAGB) was not accessible. Thus, the LAPI experiment carried its own aspect magnetometer to keep the LAPI sensors aligned with the magnetic field. The names of the sensors were given the mounting angle with respect to the downward direction of the magnetic field, and thus, represent the approximate downward directed pitch angle of the sensor. Because of the possible confusion with the normal definition of the pitch angle (the angle between the particle's velocity vector and the magnetic field), we will refer to the downward directed pitch angle of the sensor as the Precipitation angle. Thus, the mounting angles of the LAPI sensors are approximately the Precipitation angle. The sensor names reflecting the mounting angles are shown in Table 1. Table 1: LAPI sensor and their Sensor Names/Mounting Angles. LAPI SENSOR NAME or SENSOR NUMBERS MOUNTING ANGLE ELECTRON ION (DEGREES) 0 1 0+ 2 3 180- 4 5 30 6 7 172.5 8 9 7.5 10 11 45 12 13 112.5 14 15 97.5 16 17 165 18 19 60 20 21 135 22 23 105 24 25 15 26 27 180+ 28 29 0- The way the sensor names map to the CDF file is shown in Table 2. Listed are the sensor names and the CDF sensor number for the Precipitation and Pitch Angle. All angles are in degrees. In general Precipitation Angle sensors 0-6 in the CDF file were designed to measure particles traveling down, toward the Earth and Precipitation Angle sensors 7-14 in the CDF file were designed to measure particles traveling up, away from the Earth. There are times when the LAPI scan platform rotated the sensors to angles which do not follow the designated pattern. For those times, the Precipitation Angle and Pitch Angle reflect the actual position of the sensor with respect to the magnetic field. Table 2. LAPI Sensor Names/Mounting Angles and how they map to the CDF sensor. LAPI* CDF Sensor Number SENSOR NAME Precipitation Pitch 0- deg 0 15 0+ deg 1 16 7.5 deg 2 17 15 deg 3 18 30 deg 4 19 45 deg 5 20 60 deg 6 21 97.5 deg 7 22 112.5 deg 8 23 105 deg 9 24 135 deg 10 25 165 deg 11 26 172.5 deg 12 27 180+ deg 13 28 180- deg 14 29 *Note In this CDF, the LAPI 112.5 deg sensor is not in numerical order. DE-2 was designed to be a 3-axis stabilized spacecraft. However, there were times when DE-2 spun. During these times, the scanner was supposed to be in a locked position; however, there are times observed within this data where it appears as though the scan platform freely rotates. During these times, the Precipitation and Pitch angles should accurately reflect the position of the sensor with respect to the magnetic field. For the CDF file, the Pitch Angle is formed from the definition of Pitch Angle = ARCCOS {(-L vector dot B vector)/(|L|*|B|)} where - -L vector is the negative of the sensor look direction, B vector is the magnetic field vector, |L| is the magnitude of the Look vector, |B| is the magnitude of the magnetic field vector, and the look direction (L vector) is just the vector expression of the mounting angle in the sensor name. and the Precipitation angle definition is Precipitation Angle = Pitch Angle if DE-2 is in the northern Hemisphere Precipitation Angle = -Pitch Angle if DE-2 is in the southern Hemisphere Three flags in this CDF indicate the processing which occurred when computing the pitch angle. These are shown in Table 3. The first flag (0) indicates from where the magnetic field was taken. Preference goes to the values from MAGB since they are the most accurate measure of the magnetic field. A value of 0 means that the magnetic field was taken from MAGB. A value of 1 means the magnetic field was taken from the LAPI magnetometer. A value of 2 means that no magnetic field was available. Table 3. Flags which indicate the processing conditions. CDF Flag name Values CDF storing Value 0 Magnetic Field From 0, 1, 2 MAGBSC or LAPIB 1 Magnetic Latitude Unavailable 0, 1 D2OAMAGB 2 Geographic Latitude Unavailable 0, 1 D2OALAPI Judgment of the hemisphere for DE-2 should be based on the Magnetic Latitude; however, the Magnetic Latitude is not always available. The second flag (1) being 0 indicates that the Magnetic Latitude was available and was used whereas a 1 value means that no Magnetic Latitude was available. As a backup for the magnetic latitude, the third flag value of 0 indicates that the Geographic Latitude was available and a value of 1 indicates that the Geographic Latitude was not available. If the Magnetic Latitude is unavailable and the Geographic Latitude is used to assign the hemisphere, it could be incorrect in the region around the equator where the magnetic equator and the geographic equator are not aligned. If the data being analyzed is near the pole, there should be no effect. The availability of the Precipitation and Pitch angles relies of the scanner angle availability. Without knowing the scanner angle, the relation of the LAPI sensors to the magnetic field can not be determined. Thus the timing of the Precipitation and Pitch angles is at the 2 sec cadence of the scanner angle where the magnetic field is interpolated to the time the scanner angle was measured. All variables are stored as 4 byte real numbers where -3.4e+38 is used to indicate a fill value.