Subinertial Sea Surface Heights Anomalies Estimated Using High Frequency Radar Surface Current Data in the Mississippi Bight. Issue 3 (4th March 2023)

• Record Type: Journal Article
• Authors: Nwankwo, Uchenna; Howden, Stephan; Nechaev, Dmitri; Dzwonkowski, Brian
• Is Part Of: Journal of geophysical research. Volume 128:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-03-04
• Subjects: geostrophic balance -- subinertial sea level -- momentum equation -- satellite altimeter -- buoy -- high frequency radar; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2022JC019055
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Sea level studies in the Mississippi Bight (MSB) are less abundant than in other coastal waters of USA. This study investigates the subinertial (time scales >2 days) sea level anomalies in the MSB shelf. The diagnostics of the terms in the invariant form of the momentum equation were computed to determine which terms have the most influence on the anomalies in sea level. It was determined that at subinertial scales the geostrophic balance is the dominant balance in the MSB while the non‐linear and time derivative terms are insignificant relative to the Coriolis term. A Least Squares procedure was applied to the subinertial surface currents data from high frequency radar surface currents (filtered with a window of 2‐day Butterworth filter) to extract subinertial sea level anomalies in the MSB shelf using both geostrophic balance and the invariant form of Reynolds' averaged momentum equations. The resulting subinertial sea level anomalies were validated using sea level observations from an offshore buoy and Sentinel‐3 along‐track satellite altimeter data. The estimated sea level anomalies were reasonably close to observations (more than half had root mean square difference of <0.04 m) and mostly influenced by geostrophic balance. Analysis of the empirical orthogonal functions showed that the first two modes explained the majority (85%) of the variance in the sea level anomalies estimated using the geostrophic approximation. Absolute sea level could be estimated if Global Navigation Satellite System buoys are deployed in the radar footprint. Plain Language Summary: Compared to other USA coastal waters, fewer sea level studies have been conducted in the Mississippi Bight (MSB). This study focuses on slow varying sea level anomalies with periods longer than 2 days. The terms in the equation governing the circulation in the MSB were evaluated using high frequency (HF) radar velocity data to determine which terms contributed the most to the sea level anomalies. The study demonstrated that the term associated to Earth's rotation has the largest amplitude implying that the dominant balance is between this term and the term related to sea level slope. Sea level anomalies estimated from both this dominant balance and the full governing equation by applying a Least Squares procedure. Buoy and Sentinel‐3 satellite altimeter sea level observations were used not only to validate the estimated sea level anomalies but also to confirm the validity of the dominant balance. Two major patterns of sea level spatiotemporal variability were determined. They accounted for 85% of the changes in the sea level anomalies. Additional observations within the HF radar coverage area such as high quality positioning data could be used to reference the estimated sea level anomalies. Key Points: At subinertial scales geostrophic balance is dominant in the Mississippi Bight The Least Squares procedure was used to estimate reliable sea level changes on the Mississippi Bight from surface current data There are two major patterns of Mississippi Bight sea level gradient determined from EOF