Emergence Submergence Velocity Checker

Evaluate emergence w−u·grad(surface) in a fixed local horizontal/vertical frame; positive means emerging and negative submerging, without coordinate transformation or balance inference.

Description

Emergence velocity measures motion through a sloping glacier surface.

Emergence velocity measures motion through a sloping glacier surface. Vertical velocity alone is insufficient when ice also moves horizontally over the slope.^[1]

Evaluate emergence w−u·grad(surface) in a fixed local horizontal/vertical frame; positive means emerging and negative submerging, without coordinate transformation or balance inference.

When to use Emergence Submergence Velocity Checker

Use this for the following task: Evaluate emergence w−u·grad(surface) in a fixed local horizontal/vertical frame; positive means emerging and negative submerging, without coordinate transformation or balance inference.

Prepare the measurements and calibration parameters in the declared units. Keep vector entries aligned and choose a consistent spatial frame and time basis.

How to use Emergence Submergence Velocity Checker and understand its results

Prepare the measurements and calibration parameters in the declared units. Keep vector entries aligned and choose a consistent spatial frame and time basis.
Enter horizontalVelocityMPerYear, surfaceElevationGradient, verticalVelocityMPerYear using the field table, then run the tool.
Read emergenceVelocityMPerYear. Interpret flags, units, ordering and placeholder values using the rules below.
Review any reported issue or failed check, correct the supplied values when appropriate, and verify the result in its intended context.

Input field	Meaning	Value type and bounds	Requirement
horizontalVelocityMPerYear	Horizontal velocity m per year	list of number; each entry: number	Required
surfaceElevationGradient	Surface elevation gradient	list of number; each entry: number	Required
verticalVelocityMPerYear	Vertical velocity m per year	number	Required

Supply two matching horizontal components in a common local frame. Subtract their dot product with the surface gradient from vertical velocity.^[2]

emergence = verticalVelocity − horizontalVelocity · surfaceGradient

This summarizes the declared operation. Units, indexing, inclusivity and exceptional cases are explained in the surrounding text.

Output field	Meaning	Value type
emergenceVelocityMPerYear	Emergence velocity m per year	number

json

{
  "input": {
    "horizontalVelocityMPerYear": [
      10,
      20
    ],
    "surfaceElevationGradient": [
      0.1,
      0.2
    ],
    "verticalVelocityMPerYear": 3
  },
  "output": {
    "emergenceVelocityMPerYear": -2
  }
}

Limitations and assumptions

Positive means emergence and negative means submergence. No coordinate transformation or surface mass balance is inferred.

Constants and empirical coefficients are supplied rather than calibrated. Check units and observational applicability before interpreting the model. Malformed requests produce input errors. A successfully evaluated request can still contain false flags, empty result lists or a result outside the supplied threshold; those outcomes have the meanings stated above.

Alternative or Complementary methods

Choose Longitudinal Strain Rate for this operation: Estimate interval longitudinal normal strain rate from velocity gradients along a supplied flow transect; not transverse or tensor shear strain. For a complementary task, use Annual Mass Balance for this operation: Area-weight annual accumulation minus ablation over matched nonoverlapping glacier zones; quantities are water equivalent and negative balances are preserved.

Further background: Ice rheology.

References

Ice rheology — PISM
Emergence Submergence Velocity Checker — tool.io

Similar or alternative tools

Longitudinal Strain Rate
Estimate interval longitudinal normal strain rate from velocity gradients along a supplied flow transect; not transverse or tensor shear strain.
Annual Mass Balance
Area-weight annual accumulation minus ablation over matched nonoverlapping glacier zones; quantities are water equivalent and negative balances are preserved.