env-generator: analytic form 2 domes the thermocline; 48x40x26 grid (#113)

app/config/run.json

@@ -335,16 +335,16 @@
     },
     "nowcast": {
       "grid": {
-        "longitude": 96,
-        "latitude": 80,
-        "depth": 6
+        "longitude": 48,
+        "latitude": 40,
+        "depth": 26
       },
       "interval_ticks": 900,
       "time_steps": 4,
       "step_seconds": 3600
     },
     "departure": {
-      "grid": { "longitude": 48, "latitude": 40, "depth": 6 },
+      "grid": { "longitude": 48, "latitude": 40, "depth": 26 },
       "time_steps": 12,
       "step_seconds": 3600
     },
@@ -403,7 +403,8 @@
           "depth_m": 80,
           "thickness_m": 30,
           "temperature_drop_c": 4,
-          "salinity_rise_psu": 0.1
+          "salinity_rise_psu": 0.1,
+          "displacement_m_per_c": 20
         },
         "jitter": {
           "depth_m": 15,

app/src/backend/advisories/source.ts

@@ -16,7 +16,8 @@ import { Rng } from '../lib/rng.js';
 import { configDigest } from '../lib/sha256.js';
 import { HeartbeatEmitter } from '../lib/heartbeat.js';
 import { isoPlusSeconds } from '../lib/sim-time.js';
-import { backgroundTemperature, backgroundSalinity, soundSpeedMs } from '../env-generator/analytic.js';
+import { backgroundTemperature, backgroundSalinity } from '../env-generator/analytic.js';
+import { soundSpeedMs } from '../../seam/ocean-relations.js';
 import type { EnvGenerator } from '../env-generator/generator.js';
 import type { FeatureStore } from '../feature-store/store.js';
 

app/src/backend/analyst/analyst.test.ts

@@ -20,7 +20,7 @@ import type {
 } from '../../generated/types.js';
 import { createSeamValidator } from '../../seam/validate.js';
 import { buildBackend, type BackendRuntime } from '../runtime/runtime.js';
-import { soundSpeedMs } from '../env-generator/analytic.js';
+import { soundSpeedMs } from '../../seam/ocean-relations.js';
 import { driveUntil } from '../test-support/drive.js';
 
 const validator = createSeamValidator();

app/src/backend/analyst/analyst.ts

@@ -506,7 +506,17 @@ export class Analyst {
     const digest = `sha256:${sha256Hex(bytes)}`;
     const manifest: Manifest = {
       ...baseManifest,
-      generator: { name: 'drogna-analyst', version: '2.0.0', analytic_form_version: 1 },
+      // The form version travels with the parameters, and the parameters come from the
+      // manifest spread above. Typed here it was correct only while there was one form:
+      // the moment the env-generator reached form 2 (#113) this document would have
+      // carried form 2's thermocline parameters under a form 1 label, telling a reader it
+      // could reconstruct a doming layer with the flat rule. Read from the base and it
+      // cannot drift again.
+      generator: {
+        name: 'drogna-analyst',
+        version: '2.0.0',
+        analytic_form_version: baseManifest.generator.analytic_form_version,
+      },
       config_digest: configDigest(this.config),
       generated_at: { sim_time: this.simTime.value, tick: this.simTime.tick },
       grid: {

app/src/backend/env-generator/analytic.test.ts

@@ -5,11 +5,10 @@ import {
   frontAnomalyT,
   frontSignedDistanceKm,
   movingCentreAt,
-  pressureDbar,
-  soundSpeedMs,
   tauAt,
   temperatureAt,
   thermoclineAnomalyT,
+  thermoclineDepthAt,
   type WorldParameters,
 } from './analytic.js';
 
@@ -41,7 +40,7 @@ const world: WorldParameters = {
     salinity_amplitude_psu: -0.2,
     depth_scale_m: 250,
   },
-  thermocline: { depth_m: 80, thickness_m: 30, temperature_drop_c: 4, salinity_rise_psu: 0.1 },
+  thermocline: { depth_m: 80, thickness_m: 30, temperature_drop_c: 4, salinity_rise_psu: 0.1, displacement_m_per_c: 20 },
   moving: {
     centre_latitude: 45,
     centre_longitude: -12.5,
@@ -62,7 +61,7 @@ const tau = {
   feature_seconds: { eddy: 432000, front: 172800, thermocline: 1209600, moving: 86400 },
 };
 
-describe('the analytic form (v1)', () => {
+describe('the analytic form (v2)', () => {
   it('background cools and freshens towards the deep, monotonically', () => {
     let previous = Number.POSITIVE_INFINITY;
     for (const depth of [0, 50, 100, 200, 400, 800, 1000]) {
@@ -89,12 +88,52 @@ describe('the analytic form (v1)', () => {
   });
 
   it('the thermocline realises its full drop across the layer', () => {
-    const above = thermoclineAnomalyT(world.thermocline, 0);
-    const below = thermoclineAnomalyT(world.thermocline, 400);
+    const above = thermoclineAnomalyT(world.thermocline, 0, world.thermocline.depth_m);
+    const below = thermoclineAnomalyT(world.thermocline, 400, world.thermocline.depth_m);
     // Within the tanh tails: the surface sits 2.7 thicknesses above the layer.
     expect(above - below).toBeCloseTo(4, 1);
   });
 
+  it('the layer follows the features that displace it (analytic form 2)', () => {
+    /*
+     * Far from the eddy and the drifting feature the layer sits where it was authored: form 2
+     * reduces to form 1 wherever nothing local is acting, which is what makes the displacement a
+     * perturbation of the authored depth rather than a different depth scale.
+     *
+     * **The far field is quiet only because the front is not a displacement term**, which is
+     * this assertion's other job. An earlier version included it, and this test failed here at
+     * 63.9 m against 80 — the front's own saturated −1.2 °C times the coefficient, reaching the
+     * corner of the domain. A `tanh` never decays, so there is no "far" from a front, and the
+     * measurement in `thermoclineDepthAt`'s note is what that cost the drifting feature's
+     * recovery. Put the front back and this line fails first and cheapest.
+     */
+    const far = thermoclineDepthAt(world, -13.9, 44.1, 0);
+    expect(far).toBeCloseTo(world.thermocline.depth_m, 1);
+
+    // The eddy is warm-cored (sign +1), so it presses the layer down beneath it.
+    const underEddy = thermoclineDepthAt(world, world.eddy.centre_longitude, world.eddy.centre_latitude, 0);
+    expect(underEddy).toBeGreaterThan(far + 10);
+
+    // The moving feature is cold-cored (sign -1), so it domes the layer, and it takes the dome
+    // with it: the dome is under the centre at each time, not under the initial centre.
+    const start = movingCentreAt(world.moving, 0);
+    const later = movingCentreAt(world.moving, 5 * 86400);
+    expect(thermoclineDepthAt(world, start.longitude, start.latitude, 0)).toBeLessThan(far - 10);
+    expect(thermoclineDepthAt(world, later.longitude, later.latitude, 5 * 86400)).toBeLessThan(far - 10);
+    expect(thermoclineDepthAt(world, start.longitude, start.latitude, 5 * 86400)).toBeGreaterThan(
+      thermoclineDepthAt(world, later.longitude, later.latitude, 5 * 86400),
+    );
+  });
+
+  it('a zero displacement coefficient reproduces the flat layer of analytic form 1', () => {
+    // The version bump's own boundary, so "form 2 is a superset of form 1" is a checked claim
+    // rather than a sentence in a comment.
+    const flat: WorldParameters = { ...world, thermocline: { ...world.thermocline, displacement_m_per_c: 0 } };
+    for (const [lon, lat] of [[-13.9, 44.1], [world.eddy.centre_longitude, world.eddy.centre_latitude], [-9.5, 47]]) {
+      expect(thermoclineDepthAt(flat, lon, lat, 0)).toBe(flat.thermocline.depth_m);
+    }
+  });
+
   it('the moving feature advects as an exact affine map', () => {
     const day = movingCentreAt(world.moving, 86400);
     expect(day.latitude).toBeCloseTo(45 + 5 / 111.32, 6);
@@ -112,14 +151,4 @@ describe('the analytic form (v1)', () => {
     const centreLater = movingCentreAt(world.moving, 10 * 86400);
     expect(tauAt(world, tau, centreLater.longitude, centreLater.latitude, 100, 10 * 86400)).toBeCloseTo(86400, 0);
   });
-
-  it('pressure and sound speed behave at their anchors', () => {
-    expect(pressureDbar(0)).toBe(0);
-    expect(pressureDbar(1000)).toBeCloseTo(1007.5, 6);
-    // Mackenzie's own anchor: 0°C, 35 psu, surface.
-    expect(soundSpeedMs(0, 35, 0)).toBeCloseTo(1448.96, 2);
-    const mid = soundSpeedMs(10, 35, 100);
-    expect(mid).toBeGreaterThan(1480);
-    expect(mid).toBeLessThan(1500);
-  });
 });