Evidence for a Manus persistent near-surface night inversion

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Description

During the ARM Madden-Julian Oscillation (AMIE) Manus campaign period, some near-surface temperature and moisture “oddities” were brought to light and investigated. The results are documented in an ARM Technical Report by Long and Holdridge (2012). While some minor improvements in sonde launch procedures were recommended and implemented, and other factors which have some minor effect on the surface temperature and humidity values were found, the sonde profiles themselves are shown to be within the uncertainty of the instruments used. It turns out the perceived "oddities" are the result of using unforced air ventilated surface data at Manus, in combination with the brief "GTS" sonde messages along with some of the methodology used for monitoring and evaluating sonde data during the campaign. With this intense scrutiny of the Manus sondes and the availability of 8/day sonde profiles, the investigation did turn up strong evidence that a near-surface layer at the ARM Manus site persistently developed temperature inversions during the night time.

We will present an analysis of the AMIE-Manus low-level sonde and surface meteorological data showing that the inversions form most nights, with a contributing factor being the prevalent calm conditions with wind speeds only rarely greater than 4 m/s. Comparison with equivalent analyses from AMIE-Gan exhibit infrequent night inversions that only occur with surface wind speeds less than 4 m/s. The inversions have an average pressure depth of about 7 mb, but also in the nightly increase of relative humidity to an average near 90%.

Reference: Long, CN and DJ Holdridge. 2012. Investigations of Possible Low-Level Temperature and Moisture Anomalies During the AMIE Field Campaign on Manus Island. U.S. Department of Energy. DOE/SC-ARM/TR-119, http://www.arm.gov/publications/tech_reports/doe-sc-arm-tr-119.pdf.