Correct MA2 and MB2

Author: bkeepers

packages/tide-predictor/src/constituents/MA2.ts

@@ -3,7 +3,7 @@ import nc from "../node-corrections/index.js";
 
 /**
  * Lunar variational semi-diurnal constituent (μ2, mu2).
- * Doodson Number: 237.555
+ * Doodson Number: 545.555
  * Derived from Moon's orbital parameter variations; speed 27.968°/h with period ~12.87 hours.
  * Uses M2 nodal factors with complex variable modulation.
  *
@@ -12,4 +12,4 @@ import nc from "../node-corrections/index.js";
  *
  * @see https://iho.int/en/standards-and-specifications/standards/s-14 IHO Tidal Constituent Bank
  */
-export default defineConstituent("MA2", [2, -2, 2, 0, 0, 0, 0], nc.uM2, nc.fM2);
+export default defineConstituent("MA2", [2, 0, -1, 0, 0, 0, 0], nc.uM2, nc.fM2);

packages/tide-predictor/src/constituents/MB2.ts

@@ -3,13 +3,18 @@ import nc from "../node-corrections/index.js";
 
 /**
  * Lunar elliptic constituent from parameter variations.
- * Doodson Number: ~237 (lunar parameter variant)
+ * Doodson Number: ~565.555
  * Speed ~27.9°/h with period ~12.9 hours.
  * Uses M2 nodal factors (fM2/uM2).
  *
- * Warning: Not consistently defined across all sources; may be regional or application-specific.
- * Definition and amplitude vary significantly between NOAA, IHO, and Schureman references.
+ * From https://iho.int/mtg_docs/com_wg/IHOTC/IHOTC_Misc/TWCWG_Constituent_list.pdf:
+ *
+ * > MB2 was originally called Ma2 but this became ambiguous when spoken, or typed on
+ * > computers without lower case, and so it was initially changed to MA2*. However, this
+ * > in turn was thought to be clumsy and hence MB2 was finally adopted. Although
+ * > theoretically they should have the same values of u and f as M2, they are so small
+ * > that they are commonly treated as having values of u = 0 and f = 1.
  *
  * @see Schureman, P. (1958). Manual of Harmonic Analysis and Prediction of Tides
  */
-export default defineConstituent("MB2", [2, -2, 2, 0, 0, 0, 0], nc.uM2, nc.fM2);
+export default defineConstituent("MB2", [2, 0, 1, 0, 0, 0, 0], nc.uM2, nc.fM2);

packages/tide-predictor/test/constituents/index.test.ts

@@ -51,19 +51,19 @@ describe("Base constituent definitions", () => {
   });
 
   it("has correct properties for MA2 (lunar variational semi-diurnal, mu2)", () => {
-    // MA2: [2, 0, -2, 1, 0, 0, 0]
-    // Speed: 2(T+h-s) - 2h + p ≈ 27.968208°/h
+    // MA2: [2, 0, -1, 0, 0, 0, 0]
+    // Speed: 2(T+h-s) - 2h + p ≈ 28.943°/h
     expect(constituents.MA2).toBeDefined();
-    expect(constituents.MA2.speed(testAstro)).toBeCloseTo(27.968208, 2);
+    expect(constituents.MA2.speed(testAstro)).toBeCloseTo(28.943, 3);
     expect(constituents.MA2.u(testAstro)).toBeCloseTo(constituents.M2.u(testAstro), 2);
     expect(constituents.MA2.f(testAstro)).toBeCloseTo(constituents.M2.f(testAstro), 3);
   });
 
   it("has correct properties for MB2 (lunar elliptic parameter variation)", () => {
-    // MB2: [2, 0, -3, 1, 0, 1, 0]
-    // Speed: 2(T+h-s) - 3h + p + p' ≈ 27.968°/h
+    // MB2: [2, 0, 1, 0, 0, 0, 0]
+    // Speed: 2(T+h-s) - 3h + p + p' ≈ 29.025°/h
     expect(constituents.MB2).toBeDefined();
-    expect(constituents.MB2.speed(testAstro)).toBeCloseTo(27.968, 2);
+    expect(constituents.MB2.speed(testAstro)).toBeCloseTo(29.025, 2);
     expect(constituents.MB2.u(testAstro)).toBeCloseTo(constituents.M2.u(testAstro), 2);
     expect(constituents.MB2.f(testAstro)).toBeCloseTo(constituents.M2.f(testAstro), 3);
   });