Mars aeronomy conference data workshop: MAVEN LPW data

1. Mars aeronomy conference data workshop: MAVEN LPW data 05/18/2017, LASP, Boulder Chris Fowler, Laila Andersson Christopher.fowler@lasp.colorado.edu

2. LPW – a brief overview • Primarily measures thermal electrons. • Two Langmuir probes, mounted on 7.1 m booms. • Instrument operates in ‘LP’ or ‘waves’ mode. LPW operation mode LP Derive Ne, Te, Vsc from I-V curve fitting. Waves Measure wave spectra, can derive Ne from plasma line, when present. • Waves mode: • Passive (PAS): no wave sounding. • Active (ACT): wave sounding, stimulate plasma line. • Burst data: high cadence time series E field (not always available).

3. Some shameless promoting…(These papers include more details on instrument operation mode, descriptions of the data, etc.) • Andersson et al., 2015, The Langmuir Probe and Waves (LPW) instrument for MAVEN, Space Science Reviews. • Ergun et al., 2015, Dayside electron temperature and density profiles at Maras: First results from the MAVEN Langmuir probe and waves instrument, GRL. • Fowler et al., 2015, The first in situ electron temperature and density measurements of the Martian nightside ionosphere, GRL. • Andrews et al., 2015, Ionospheric plasma density variations observed at Mars by MAVEN/LPW, GRL.

4. LPW level 2 data products – an overview • Products / CDF files available from SDC: • Ne, Te, Vsc (LP). • Ne (waves). • Wave spectra (ACT). • Wave spectra (PAS). • Burst data (LF, MF, HF). • LP I-V sweeps. • CDF files can be downloaded manually from PDS. • Recommend using the Berkeley IDL tplot software: CDF readers written in IDL to automatically download requested files and load into IDL, for manipulation. (This is the software I will demonstrate today).

5. What’s in a typical LPW CDF file (part 1)? • Naming structure example: mvn_lpw_l2_lpnt_20150402_v02_r03.cdf • Color codes: • mvn, l2: MAVEN mission, L2 data. • lpw: instrument identifier. • lpnt: specific to each instrument; data product identifier: • lpnt: Ne, Te, Vsc(LP). • lpiv: I-V sweep. • wn: Ne (waves). • wspecact: ACT spectra. • wspecpas: PAS spectra. • we12burstlf: LF burst data (time series). • we12burstmf: MF burst data (time series). • we12bursthf: HF burst data (time series). • 20150402: UTC day that the file spans. • v02_r03: Version and revision numbers. Higher = more recent.

6. What’s in a typical LPW CDF file (part 2)? Mvn_lpw_l2_lpnt_20150402_v02_r03.cdf epoch: TT2000 timestamps. data: The data: eg: Ne, Te, Vsc. time_unix: UNIX timestamps (for tplot). ddata_lo: Lower uncertainties. ddata_up: Upper uncertainties. flag: Quality flag; 0-100, recommend using >50. info: Further calibration information. Descriptions of each field within variable attributes.

7. What’s in a typical LPW CDF file (part 3)? • Example plot (using Autoplot) from the previous CDF file.

8. Periapsis passes every ~4.5 hours. Loading LPW data using IDL: IDL code is based upon the Berkeley SSL tplot software: Electron density, Ne • Set time range: Timespan, ‘2015-04-01’, 1. • Specify LPW products: mvn_lpw_load_l2, [‘lpnt’, ‘wspecact’] Electron temperature, Te Spacecraft potential, Vsc ACT spectra

9. Electron density, Ne One periapsis: Electron temperature, Te Spacecraft potential, Vsc Plasma line enables derivation of Ne from waves data. LP flag info ACT spectra Caveats for LP and waves data discussed in coming slides

10. Caveats of using the LP data (summary): • LPW was designed to measure high density plasma; Ne, Te and Vsc from LP are most accurate for Ne >~100 cm-3. LP derived quantities are thus biased towards higher densities. • The upper and lower uncertainties on each quantity are derived from the I-V curve fitting process. • LP derived quantities have large uncertainties when Vsc goes highly negative. Recommend using data for Vsc > -6V. • LPW boom1 can measure Te down to about 500 K; boom2 to about 700 K. Boom 1 and 2 data can be distinguished using the calibration information within each CDF file. Boom 2 data are not available after ~1 year. • Spacecraft operations and the local plasma environment can distort LPW I-V sweeps, making it harder to derive quantities. Such effects are accounted for (as best as possible) during L2 production, and reflected within the flag information. • Ne, Te and Vsc are derived from the same I-V sweep and are thus at identical time cadences. In some instances, one or more quantity may be unavailable (NaN’d out), while others are present. • Pay attention to the flag information! Paper describing these caveats is currently in preparation for submission to JGR.

11. Caveats of using the waves density data (summary): • Waves data are not available on a regular basis after 2015-12-09. • Ne can only be derived when the local plasma line is present (observed mainly in the ACT spectra). • LP and waves densities agree well within specific frequency ranges: • Ne < 1x103 cm-3 and Ne > 2x104cm-3 = good agreement (within ~25%). • 1x103 cm-3 < Ne < 2x104 cm-3 = Waves Ne can be up to a factor of ~2 too small due to spacecraft wake effects. • For Ne > 2.3x104 cm-3, plasma line outside of instrument frequency range and waves Ne cannot be derived. • See next slide for graphical representation of these ranges. Paper describing these caveats is currently under review in JGR.

12. Joining of the LF, MF, HF bands. • Calibration across the bands. • Low quality data removed. • Low quality data removed. • Plasma line. • Aliasing when Ne > 2.3x104 cm-3. • Low frequency noise. Spacecraft wake means waves Ne can be up to half the true ambient value. Fowler et al., 2017, Electric and magnetic variations at Mars, JGR, under review.

13. Key takeaway points: • LP data is most accurate under high density (Ne > ~ 100 cm-3) conditions. • Wave spectra have several caveats that can be mistaken as real signals. • Pay attention to the quality flag information! • Email contacts for further information regarding LPW data: • Laila.andersson@lasp.colorado.edu • Christopher.fowler@lasp.colorado.edu • Marcin.Pilinski@lasp.colorado.edu