Flare Energetics and CME/Flare Timescales
E_free(2000 G) = 2.39e+29 J, a factor of (2000/2800)^2 = 0.51 relative to the lab's value (4.68e+29 J) -- confirming the B^2 scaling, since free energy depends on the square of the field strength at fixed volume.
| Criterion | Points |
|---|---|
| Correct free-energy recomputation | 8 |
| Correct confirmation of B^2 scaling | 7 |
X1.8 flux = 1.8e-4 W/m^2. C4.5 flux = 4.5e-6 W/m^2. Ratio = 40 -- an X1.8 flare has 40 times the peak flux of a C4.5 flare, directly illustrating the classification scheme's logarithmic (decade-per-letter) structure.
| Criterion | Points |
|---|---|
| Correct flux values for both classes | 8 |
| Correct ratio computed | 7 |
Light travel time = 8.32 minutes. At a hypothetical 24-hour transit, ratio = 173; at the real ~36-hour transit, ratio = 260 -- the real event's lag between radiation arrival and CME arrival is longer than the hypothetical 24-hour case, since 36 hours exceeds 24 hours.
| Criterion | Points |
|---|---|
| Correct light-travel-time computation | 5 |
| Correct ratio computation for both cases and correct comparative direction | 5 |
Effective average speed = 1 AU / (36 hr) = 1154 km/s, substantially lower than the initial LASCO speed (1571 km/s) -- implying substantial average deceleration during transit, consistent with Lecture 07's drag-based propagation physics (the CME decelerating toward the ambient, much slower solar wind speed).
| Criterion | Points |
|---|---|
| Correct effective-speed arithmetic | 8 |
| Correct deceleration interpretation | 7 |
Award full marks for correct method, units, and a numeric result consistent with the arithmetic shown (allow reasonable rounding). Verify that the student re-derives the number for this problem's specific inputs rather than quoting a lecture example without adaptation. Watch specifically for unit-conversion errors (Gauss vs Tesla, nT vs T, km/s vs m/s, hours vs seconds), for comparative-magnitude statements given in the wrong direction, and for level-1/level-2/level-3 data-provenance conflation (e.g., presenting the order-of-magnitude flare free-energy estimate as a precise measurement, or presenting a Carrington-Dst estimate as a directly measured historical value) -- these are the most common sources of mistakes in this course.