SWP Solar Wind & Interplanetary Medium 2 — Questions and Answers
Question 1: The transit time of a CME from the Sun to Earth at 1 AU typically ranges from:
- Hours to 2 days
- 1–3 days (Correct answer)
- 5–10 days
- 2–4 weeks
Correct answer: 1–3 days
Most CMEs travel between about 300 and 2000 km/s, yielding a typical Sun-to-Earth transit time of 1 to 3 days, though extreme events can arrive in under 17 hours.
Question 2: Solar wind dynamic pressure (nmpv²) is important to magnetospheric forecasting because:
- Higher pressure compresses the magnetopause earthward, intensifying field-aligned currents (Correct answer)
- It determines the solar wind speed directly
- It measures the southward IMF Bz component
- Dynamic pressure controls auroral zone width independently of Bz
Correct answer: Higher pressure compresses the magnetopause earthward, intensifying field-aligned currents
Increased solar wind ram pressure compresses the magnetosphere, moving the magnetopause inward and energizing ring current and field-aligned current systems.
Question 3: A 'magnetic cloud' is a subset of CMEs identified by:
- Very high solar wind density and temperature
- Smoothly rotating magnetic field, low proton temperature, and low plasma beta (Correct answer)
- Extremely high solar energetic proton flux
- Strong northward IMF Bz lasting more than 24 hours
Correct answer: Smoothly rotating magnetic field, low proton temperature, and low plasma beta
Magnetic clouds show the classic flux rope signature: rotating IMF vector, depressed proton temperature (indicating expansion), and low beta (magnetic pressure dominates over thermal).
Question 4: The Forbush decrease is a reduction in galactic cosmic ray flux at Earth caused by:
- Geomagnetic storm ring current shielding
- CME passage shielding Earth's environs with a magnetically closed structure that deflects cosmic rays (Correct answer)
- Solar energetic particle flux overwhelming cosmic ray sensors
- Earth's orbit moving to higher heliolatitude
Correct answer: CME passage shielding Earth's environs with a magnetically closed structure that deflects cosmic rays
As a CME and its magnetic sheath pass Earth, the enhanced and disordered magnetic fields within the CME structure scatter and exclude galactic cosmic rays, causing a temporary flux decrease.
Question 5: Which instrument aboard DSCOVR provides the primary real-time solar wind data used for space weather operations?
- Magnetograph
- Faraday cup / electron electrostatic analyzer (plasma instrument) and fluxgate magnetometer (Correct answer)
- X-ray irradiance monitor
- Coronagraph
Correct answer: Faraday cup / electron electrostatic analyzer (plasma instrument) and fluxgate magnetometer
DSCOVR's PlasMag instrument suite includes a Faraday cup for solar wind density/speed/temperature and a fluxgate magnetometer for IMF Bx, By, Bz — the key operational inputs for storm forecasting.
Question 6: Alfvén waves in the solar wind are important for space weather because:
- They carry most of the solar wind kinetic energy
- They transmit fluctuations in IMF direction that drive magnetospheric convection and substorm activity (Correct answer)
- They accelerate solar energetic particles to relativistic speeds
- They are the primary driver of radiation belt electron loss
Correct answer: They transmit fluctuations in IMF direction that drive magnetospheric convection and substorm activity
Alfvénic fluctuations produce oscillations in the IMF orientation, including southward Bz excursions that drive intermittent magnetospheric energy injection and substorm triggering.
SWP Solar Wind & Interplanetary Medium 2
The transit time of a CME from the Sun to Earth at 1 AU typically ranges from: