Sea Surface Height Anomaly Calculator
Calculate sea surface height anomaly with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Formula
SSHA = SSH_observed - SSH_mean; DOT = SSH - N
SSHA is sea surface height anomaly, SSH is height above reference ellipsoid, N is geoid height, DOT is dynamic ocean topography.
Worked Examples
Example 1: Western Pacific Warm Pool
Problem: Altimeter measures SSH 0.25 m above mean. Geoid -28 m. Steric anomaly 0.12 m. Tidal correction 0.03 m.
Solution: SSHA = 0.25 - 0 = 25 cm\nCorrected = 25 - 3 = 22 cm\nSteric = 12 cm, Mass = 10 cm\nGeostrophic V = (9.81/1e-4)(0.25/100000) = 0.025 m/s
Result: SSHA: 25 cm | Corrected: 22 cm | Geostrophic: 0.025 m/s
Example 2: Cold Core Eddy
Problem: Cyclonic eddy: SSH -0.10 m below mean. Geoid -35 m. Steric -0.06 m. Tidal correction 0.01 m.
Solution: SSHA = -10 cm\nCorrected = -11 cm\nSteric = -6 cm, Mass = -5 cm\nGeostrophic V = 0.010 m/s
Result: SSHA: -10 cm | Mass: -5 cm | Geostrophic: 0.010 m/s
Frequently Asked Questions
What is sea surface height anomaly?
Sea surface height anomaly is the difference between instantaneous sea surface height and the long-term mean at that location. It captures time-varying ocean topography caused by currents eddies tides and atmospheric pressure variations. SSHA is measured by satellite radar altimeters determining satellite-to-surface distance with centimeter precision. Positive anomalies indicate higher-than-average sea level associated with warm water or anticyclonic eddies while negative anomalies indicate lower-than-average levels. SSHA maps are essential for monitoring ocean circulation El Nino events and sea level rise.
How do satellite altimeters measure sea surface height?
Satellite radar altimeters emit microwave pulses toward the ocean surface measuring precise round-trip travel time to determine satellite-to-surface distance. Satellite altitude above a reference ellipsoid is independently determined using GPS DORIS and satellite laser ranging. Subtracting range from altitude gives sea surface height above the reference ellipsoid. Multiple corrections are applied including ionospheric delay tropospheric wet and dry path delays sea state bias and tidal effects. Missions like Jason-3 Sentinel-6 and SWOT have provided continuous global records since 1992.
What is the steric component of sea level change?
The steric component refers to volume changes caused by temperature and salinity variations without adding or removing water mass. Thermal expansion occurs when ocean water warms and expands raising sea level without new water addition. Halosteric effects from salinity changes are generally smaller globally. The steric contribution to global mean sea level rise is currently about 1.3 mm per year roughly one-third of total observed rise. Argo profiling floats measure temperature and salinity throughout the upper 2000 meters providing data to calculate steric changes globally.
How do tides affect sea surface height measurements?
Tides can cause sea surface height variations of several meters completely overwhelming centimeter-scale oceanographic signals. Ocean tide models predict tidal heights with 1 to 2 centimeter accuracy in the open ocean and are used to remove tidal signals. Solid Earth tides cause the ocean floor to rise and fall by up to 30 centimeters requiring correction. The pole tide from Earth rotation wobble produces up to 2 centimeter response. Loading tides from crustal deformation under tidal water weight add further corrections. Residual tidal errors remain a major uncertainty source in altimetric measurements.
What is the inverse barometer effect on sea level?
The inverse barometer effect describes ocean surface response to atmospheric pressure changes where a 1 hectopascal increase depresses the surface by approximately 1 centimeter. The ocean adjusts hydrostatically with high pressure pushing the surface down and low pressure allowing it to rise. The effect can cause 10 to 20 centimeter variations during major weather systems and must be corrected in altimetric data. The correction uses atmospheric pressure analyses from weather prediction models. In enclosed basins like the Mediterranean the adjustment is incomplete requiring modified corrections.
How does El Nino affect sea surface height anomalies?
El Nino produces dramatic SSHA changes across the tropical Pacific with positive anomalies of 20 to 30 centimeters in the central and eastern equatorial Pacific and negative in the west. These changes are driven by relaxation of easterly trade winds which normally pile warm water westward. When winds weaken equatorial Kelvin waves propagate eastward redistributing warm water. Satellite altimetry provides real-time monitoring and has become critical for tracking onset evolution and decay of El Nino events. The 1997-1998 El Nino was among the first major events continuously monitored by altimeters.