Ship- and island-based soundings from the 2016 El Niño Rapid Response (ENRR) field campaign

Abstract

Abstract. As the 2015/2016 El Niño was gathering strength in late 2015, scientists at the Earth System Research Laboratory's Physical Sciences Division proposed and led the implementation of NOAA's El Niño Rapid Response (ENRR) Field Campaign. ENRR observations included wind and thermodynamic profiles of the atmosphere over the near-equatorial east-central Pacific Ocean, many of which were collected from two field sites and transmitted in near-real time for inclusion in global forecasting models. From 26 January to 28 March 2016, twice-daily rawinsonde observations were made from Kiritimati (pronounced Christmas) Island (2.0°N, 157.4°E; call sign CXENRR). From 16 February to 16 March 2016, three to eight radiosondes were launched each day from the NOAA Ship Ronald H. Brown (allocated call sign WTEC) as it travelled southeast from Hawaii to service Tropical Atmosphere Ocean (TAO) buoys along longitudes 140°W and 125°W and then north to San Diego, California. Both the rapid and the remote nature of these deployments created particular difficulties in collecting and disseminating the soundings; these are described together with the methods used to reprocess the data after the field campaign finished. The reprocessed and lightly quality-controlled data have been put into an easy-to-read text format, qualifying them to be termed Level 2 soundings. They are archived and freely available for public access at NOAA's National Centers for Environmental Information (NCEI) in the form of two separate data sets: one consisting of 125 soundings from Kiritimati Island (doi:10.7289/V55Q4T5K), the other of 193 soundings from the NOAA Ship Ronald H. Brown (doi:10.7289/V5X63K15). Of the Kiritimati soundings, 94 % reached the tropopause and 88 % reached 40 hPa, while 89 % of the ship's soundings reached the tropopause and 87 % reached 40 hPa. The soundings captured the repeated advance and retreat of the ITCZ at Kiritimati, a variety of marine tropospheric environments encountered by the ship, and lower-stratospheric features of the 2015–2016 QBO (quasi-biennial oscillation), all providing a rich view of the local atmosphere's response to the east-central Pacific's extremely warm waters during the 2015/16 El Niño.

Central-Pacific surface meteorology from the 2016 El Niño Rapid Response (ENRR) field campaign

“…Airflow distortion caused by the superstructure of the ship can result in localized pressure anomalies. We compared the ship pressure with the pressure observed by the radiosondes while the radiosondes equilibrated outside on the fantail of the ship (see Hartten et al, 2018). This analysis revealed a bias in the ship pressure as a function of relative wind direction that is approximately 0.007 hPa per degree of relative wind direction (r = −0.46, p < 0.001): positive when the winds are incident upon the port side, negative when they are incident upon the starboard side, and near zero when the relative wind direction is aligned along the ship's length.…”

Central-Pacific surface meteorology from the 2016 El Niño Rapid Response (ENRR) field campaign

“…Among the many assets put into play were surface meteorological instruments on 25 Kiritimati (pronounced "Christmas") Island and aboard the NOAA Ship Ronald H. Brown. The primary purpose of the surface meteorological measurements was to provide initialization data for the radiosondes launched twice a day from Kiritimati and four to eight times per day from the NOAA Ship Ronald H. Brown (Hartten et al, 2017a). However, the high temporal resolution of the surface measurements in these remote locations makes them useful in their own right.…”