Long Wave Measurement Corrections for the OMNI Buoy Network

Jossia Joseph, National Institute of Ocean Technology, Ocean Observation Systems, Chennai, India, Amit Tandon, University of Massachusetts, Dartmouth, Mechanical Engineering, Dartmouth, United States, Venkatesan Ramasamy, National Institute of Ocean Technology, Ocean Observation Systems, Chennai, TN, India, J. Thomas Farrar, Woods Hole Oceanographic Inst, Department of Physical Oceanography, Woods Hole, United States and Robert A Weller, WHOI, Monument Beach, MA, United States
Abstract:
The inception of moored buoy network in Indian Seas in 1997 paved the way for systematic collection of long-term time series observations of meteorological and oceanographic parameters which got revamped with OMNI (Ocean Moored buoy network for North Indian ocean) buoys in 2011. Radiation sensors were installed on the OMNI buoys to better estimate the air-sea fluxes, important for cyclone forecasting as well as in assessing the different modes of monsoon and upper ocean dynamics. However, the inter-comparison of OMNI buoy measurements in northern Bay of Bengal with the nearby WHOI mooring during the year 2015 exhibited an overestimation of downwelling long wave radiation (LWR_D) measured using Eppley Precision Infrared Radiometer. The overestimation is analyzed in detail by comparing the time series measurements of raw data from the collocated radiation sensors of OMNI and WHOI established at the reference station at NIOT (National Institute of Ocean Technology) from January to March 2019. This shows that the fine tuning of the thermopile voltage records (or amplifier) along with the customized data logger in the WHOI setup leads to better estimations of the LWR_D values. The offset for the LWR_D measurements by the OMNI sensor is estimated by segregating the clear sky conditions identified by using the downwelling short wave measurements from the same reference station. The comparison of corrected LWR_D with that of collocated WHOI measurements exhibited a good agreement, with a correlation of 0.95 and standard deviation of 5.7 W/m2. This method is applied in correcting the field measurements and is again compared with the nearby WHOI buoy measurements, which exhibits better match in the downwelling fluxes without any offset. This study is leading to the revamping of radiation measurements in OMNI buoys and it is providing a reliable method to correct the past measurements as well as the better estimation of air-sea fluxes.

Key words: OMNI buoys, North Indian Ocean, long wave radiation, Bay of Bengal, air-sea fluxes

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