Added a basic Harris-Priester model (with one change for smoothness)
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#!/usr/bin/env python3
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"""Regenerates src/atmosphere/space_weather.rs, the drivers a density model reads.
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Usage: scripts/fetch-space-weather.py [path to a local copy of the source file]
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The record is emitted as Rust rather than as data to parse, the same way the gravity
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coefficients are. Nothing at runtime reads a file or validates a field.
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Unlike the gravity coefficients and the kernels, this record is *meant* to change: it gains
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a row a day. So there is no digest to pin it to. What this records instead is the digest of
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what was downloaded, with the date and the coverage, in the output's own header —
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provenance for a file that moves rather than a lock on one that does not.
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Source: GFZ Potsdam's combined Kp/ap/Ap/SN/F10.7 record. Chosen over Celestrak's
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SW-All.csv for two reasons. It carries an explicit license where Celestrak states none, and
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that matters for a file committed into an MIT crate. And Celestrak's runs decades past
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today on its own predictions, which are not measurements; a propagation that silently used
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them would not be reproducible.
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The sunspot column is dropped. It is the one part of the GFZ file under CC BY-NC 4.0 rather
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than CC BY 4.0, and no density model here wants it.
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"""
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import hashlib
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import subprocess
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import sys
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from datetime import date, timedelta
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from pathlib import Path
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URL = "https://kp.gfz-potsdam.de/app/files/Kp_ap_Ap_SN_F107_since_1932.txt"
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ATTRIBUTION = (
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"GFZ German Research Centre for Geosciences and Geomagnetic Observatory Niemegk, "
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"CC BY 4.0"
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)
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MISSING = -1.0
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# Geomagnetic indices reach back to 1932 and the solar flux to February 1947, but the early
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# flux record is sporadic — 105 missing days in 1947 and one hole of 44. From 1957 it is all
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# but complete: 39 gaps in seventy years, none longer than five days, none longer than two
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# since 2020. So that is where the retained record starts, which is also where the other
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# published driver files start.
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START = date(1957, 1, 1)
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# A run of unmeasured days this long is refused rather than interpolated. Five is the worst
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# the source holds from 1957 on, so this leaves room for it to change without quietly
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# inventing a fortnight of weather.
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LONGEST_FILL = 7
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ROOT = Path(__file__).resolve().parent.parent
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OUT = ROOT / "src" / "atmosphere" / "space_weather.rs"
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# Modified Julian Day zero. The record is indexed by MJD because a UT day is not always
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# 86400 seconds and MJD still increments by exactly one across a leap second.
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MJD_EPOCH = date(1858, 11, 17)
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# Field positions in the source, which is whitespace-aligned with 28 columns.
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YEAR, MONTH, DAY = 0, 1, 2
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AP_FIRST, AP_LAST = 15, 22
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AP_DAILY = 23
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F107_OBSERVED, F107_ADJUSTED = 25, 26
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DEFINITIVE = 27
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def source_text(argv):
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if len(argv) > 1:
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raw = Path(argv[1]).read_bytes()
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print(f"reading {argv[1]}")
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else:
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print(f"downloading {URL}")
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raw = subprocess.run(
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["curl", "-sS", "--fail", "--max-time", "180", "-L", URL],
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check=True,
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capture_output=True,
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).stdout
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return raw.decode(), hashlib.sha256(raw).hexdigest()
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def parse(text):
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"""Daily rows from START onward, with the flux left as None where unmeasured."""
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rows = []
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for line in text.splitlines():
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if line.startswith("#") or not line.strip():
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continue
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fields = line.split()
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if len(fields) != 28:
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raise SystemExit(f"expected 28 fields, found {len(fields)}: {line[:60]}")
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when = date(int(fields[YEAR]), int(fields[MONTH]), int(fields[DAY]))
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if when < START:
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continue
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def flux(at):
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value = float(fields[at])
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return None if value <= MISSING else value
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rows.append(
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{
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"date": when,
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"ap": [int(float(f)) for f in fields[AP_FIRST : AP_LAST + 1]],
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"ap_daily": int(float(fields[AP_DAILY])),
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"observed": flux(F107_OBSERVED),
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"adjusted": flux(F107_ADJUSTED),
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"definitive": int(fields[DEFINITIVE]),
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"filled": False,
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}
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)
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if not rows:
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raise SystemExit(f"no rows at or after {START}")
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# The record is addressed by day, so a missing date would shift everything after it.
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for earlier, later in zip(rows, rows[1:]):
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if later["date"] - earlier["date"] != timedelta(days=1):
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raise SystemExit(f"missing day between {earlier['date']} and {later['date']}")
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return rows
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def trim(rows):
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"""Drops any unmeasured days at either end.
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START is a round date rather than a measurement, and the flux happens not to have been
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taken on it. The far end matters more: an unmeasured day there would have to be
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extrapolated rather than interpolated, and the whole point of refusing to propagate
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past the record is not to do that.
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"""
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measured = [index for index, row in enumerate(rows) if row["observed"] is not None]
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if not measured:
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raise SystemExit("no measured solar flux at all")
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return rows[measured[0] : measured[-1] + 1]
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def fill(rows):
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"""Interpolates the days the flux was not measured, marks them, counts them.
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The gaps are isolated — one or two days, five at the very worst — and the flux moves a
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few percent over that, so a straight line between the measurements either side is a
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fair reconstruction. A long gap is not, and is refused.
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"""
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measured = [index for index, row in enumerate(rows) if row["observed"] is not None]
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filled = 0
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for before, after in zip(measured, measured[1:]):
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span = after - before
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if span == 1:
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continue
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if span - 1 >= LONGEST_FILL:
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raise SystemExit(
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f"{span - 1} unmeasured days from {rows[before + 1]['date']}, too many "
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f"to interpolate"
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)
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for offset in range(1, span):
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weight = offset / span
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for key in ("observed", "adjusted"):
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rows[before + offset][key] = (
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rows[before][key] * (1.0 - weight) + rows[after][key] * weight
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)
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rows[before + offset]["filled"] = True
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filled += 1
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return filled
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def main():
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text, digest = source_text(sys.argv)
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rows = trim(parse(text))
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filled = fill(rows)
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print(f"digest {digest}")
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print(f"interpolated {filled} unmeasured days of {len(rows)}")
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OUT.parent.mkdir(parents=True, exist_ok=True)
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OUT.write_text(rust_source(rows, digest, date.today().isoformat(), filled))
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print(
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f"wrote {OUT.relative_to(ROOT)}: {len(rows)} days, "
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f"{rows[0]['date']} to {rows[-1]['date']}, {OUT.stat().st_size / 1e6:.1f} MB"
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)
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def mjd(when):
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return when.toordinal() - MJD_EPOCH.toordinal()
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def wrapped(tokens, width=96, indent=" "):
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"""The tokens as comma-separated lines, packed to `width`."""
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lines, line = [], indent
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for token in tokens:
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piece = token + ","
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if len(line) + len(piece) > width and line != indent:
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lines.append(line)
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line = indent
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line += piece
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if line != indent:
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lines.append(line)
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return "\n".join(lines)
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def array(name, kind, doc, tokens, count):
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return (
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f"{doc}\n#[rustfmt::skip]\npub(super) static {name}: [{kind}; {count}] = [\n"
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f"{wrapped(tokens)}\n];\n"
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)
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def rust_source(rows, digest, downloaded, filled):
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"""The generated module: provenance in the docs, the record in six flat arrays."""
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first, last = rows[0]["date"], rows[-1]["date"]
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doc = f"""//! Solar and geomagnetic drivers for atmospheric density, one row per UT day.
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//!
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//! Generated by `scripts/fetch-space-weather.py`; do not edit by hand. Committed as Rust
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//! rather than as data so that a clone needs no network, no data directory and no parser.
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//!
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//! Source: <{URL}>
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//! downloaded {downloaded}, SHA-256 `{digest}`.
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//!
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//! Attribution: {ATTRIBUTION}.
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//!
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//! The digest records what was downloaded rather than pinning it: the source gains a row a
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//! day, so there is nothing fixed to pin. Its sunspot column is dropped, being the one part
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//! of it under a non-commercial license.
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//!
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//! Coverage: {first} to {last}, {len(rows)} days. Geomagnetic indices reach back to 1932
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//! and the flux to 1947, but the early flux record is too sporadic to use: 105 missing days
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//! in 1947 and one hole of 44. Of the days here, {filled} had no flux measurement and were
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//! interpolated from their neighbors, never more than five in a row.
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"""
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parts = [
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doc,
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f"/// Modified Julian Day of the first row, {first}.\n"
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f"pub(super) const FIRST_DAY: i64 = {mjd(first)};\n",
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f"/// How many days the record holds.\npub(super) const DAYS: usize = {len(rows)};\n",
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array(
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"AP",
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"[f64; 8]",
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"/// The eight three-hour geomagnetic indices of each day, earliest first.",
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["[" + ",".join(f"{v}." for v in row["ap"]) + "]" for row in rows],
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"DAYS",
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),
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array(
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"AP_DAILY",
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"f64",
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"/// The daily mean geomagnetic index.",
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[f"{row['ap_daily']}." for row in rows],
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"DAYS",
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),
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array(
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"FLUX_OBSERVED",
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"f64",
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"/// Solar flux as measured, in solar flux units.",
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[f"{row['observed']:.1f}" for row in rows],
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"DAYS",
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),
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array(
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"FLUX_ADJUSTED",
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"f64",
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"/// Solar flux scaled to one astronomical unit.",
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[f"{row['adjusted']:.1f}" for row in rows],
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"DAYS",
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),
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array(
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"DEFINITIVE",
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"bool",
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"/// Whether the geomagnetic indices are settled rather than preliminary.",
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["true" if row["definitive"] else "false" for row in rows],
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"DAYS",
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),
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array(
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"FLUX_MEASURED",
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"bool",
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"/// Whether the flux was measured that day rather than interpolated across a gap.",
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["false" if row["filled"] else "true" for row in rows],
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"DAYS",
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),
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]
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return "\n".join(parts)
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if __name__ == "__main__":
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main()
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