The upper-air sounding network for Dynamics of the Madden-Julian Oscillation (DYNAMO) has provided an unprecedented set of observations for studying the MJO over the Indian Ocean, where coupling of this oscillation with deep convection first occurs. With 72 rawinsonde sites and dropsonde data from 13 aircraft missions, the sounding network covers the tropics from eastern Africa to the western Pacific. In total nearly 26 000 soundings were collected from this network during the experiment's 6-month extended observing period (from October 2011 to March 2012). Slightly more than half of the soundings, collected from 33 sites, are at high vertical resolution. Rigorous post-field phase processing of the sonde data included several levels of quality checks and a variety of corrections that address a number of issues (e.g., daytime dry bias, baseline surface data errors, ship deck heating effects, and artificial dry spikes in slow-ascent soundings).Because of the importance of an accurate description of the moisture field in meeting the scientific goals of the experiment, particular attention is given to humidity correction and its validation. The humidity corrections, though small relative to some previous field campaigns, produced high-fidelity moisture analyses in which sonde precipitable water compared well with independent estimates. An assessment of operational model moisture analyses using corrected sonde data shows an overall good agreement with the exception at upper levels, where model moisture and clouds are more abundant than the sonde data would indicate.

This study examines the westward-propagating convective disturbances with quasi-2-day intervals of occurrence identified over Gan Island in the central Indian Ocean from mid- to late October 2011 during the Dynamics of the Madden–Julian Oscillation (DYNAMO) field campaign. Atmospheric sounding, satellite, and radar data are used to develop a composite of seven such disturbances. Composites and spectral analyses reveal that 1) the quasi-2-day convective events comprise westward-propagating diurnal convective disturbances with phase speeds of 10–12 m s−1 whose amplitudes are modulated on a quasi-2-day time scale on a zonal scale of ~1000 km near the longitudes of Gan; 2) the cloud life cycle of quasi-2-day convective disturbances shows a distinct pattern of tropical cloud population evolution—from shallow to deep to stratiform convection; 3) the time scales of mesoscale convective system development and boundary layer modulation play essential roles in determining the periodicity of the quasi-2-day convective events; and 4) in some of the quasi-2-day events there is evidence of counterpropagating (westward and eastward) cloud systems along the lines proposed by Yamada et al. Based on these findings, an interpretation is proposed for the mechanisms for the quasi-2-day disturbances observed during DYNAMO that combines concepts from prior studies of this phenomenon over the western Pacific and Indian Oceans.

This study examines the DigiCORA and Global Climate Observing System Reference Upper-Air Network (GRUAN) humidity corrections of Vaisala RS92 radiosondes at three sites over the tropical Indian Ocean and surrounding areas during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign in 2011. The proprietary DigiCORA correction algorithm is built into the ground station software provided by Vaisala, whereas the GRUAN correction is an open source algorithm. Included in the GRUAN data product are uncertainty estimates for their corrections. This information is used to examine the statistical consistency of the various corrections.In general, the algorithms produce a positive relative humidity (RH) correction that increases with altitude related primarily to a solar radiation dry bias adjustment. For example, in daytime soundings the relative RH correction increases from a few percent for temperatures .08C to 20%-40% between 100 and 200 hPa. Comparison of corrected RH vertical profiles show only small differences (on the order of a few percent or less at any given level) between the DigiCORA and GRUAN algorithms, such that these corrections are considered to be statistically consistent at most levels.In evaluating corrected humidity data with independent estimates of total precipitable water (TPW), good agreement was found at all sites between corrected sounding and ground-based microwave radiometer (MWR) estimates of TPW with mean differences #0.9 mm (or ,2%), which is well within the uncertainty of these measurements. Overall, the correction algorithms examined herein perform well over a wide range of tropical moisture conditions.

Abstract. In this study, we introduce a newly developed upper-air observational instrument for atmospheric research. The “Storm Tracker” is an ultra-lightweight (about 20 g including battery), multi-channel simultaneous capable radiosonde designed by the Department of Atmospheric Sciences at National Taiwan University. Developed in 2016, the Storm Tracker aims to provide an alternative for observing atmospheric vertical profiles with a high temporal resolution, especially the lower-level atmosphere under severe weather conditions such as extreme thunderstorms and tropical cyclones. Field experiments were conducted as trial runs in Wu-Chi, Taichung, Taiwan, to examine the ability of the Storm Tracker to observe the boundary layer, in addition to the intercomparison between the Storm Tracker and the widely used Vaisala RS41-SGP radiosonde. Among the co-launches of the Storm Tracker and Vaisala RS41 radiosondes, the measurements of pressure, wind speed, and wind direction are highly consistent between the measurements of the Storm Tracker and the Vaisala RS41-SGP. However, a significant daytime warm bias in the Storm Tracker was found due to solar heating. A metal shield specifically for the Storm Tracker was thus installed and showed mitigation for the warm biases and the overall variance. With the much lower costs of the radiosondes and the simultaneous multi-channel receiver, the Storm Tracker system has shown great potential for high-frequency observational needs in atmospheric research.

Abstract. In this study, we introduce a newly-developed upper-air observational instrument for atmospheric research. The Storm Tracker (or NTU mini-Radiosonde), is an ultra-lightweight (about 20 g including battery), multi-channel simultaneous capable radiosonde designed by the Department of Atmospheric Sciences at National Taiwan University. Developed since 2016, the Storm Tracker aims to provide an alternative for observation of atmospheric vertical profiles with a high temporal resolution, especially lower-level atmosphere under severe weather such as extreme thunderstorms and tropical cyclones. Two field experiments were conducted as trial runs in December 2017 and July 2018 at Wu-Chi, Taichung, Taiwan, to compare the Strom Tracker with the widely used Vaisala RS41 radiosonde. Among 53 co-launches of the Storm Tracker and Vaisala RS41 radiosondes, the raw measurements of pressure, wind speed, and wind direction are highly consistent between the Strom Tracker and Vaisala RS41. However, a significant daytime warm bias was found due to solar heating. A metal shield specifically for the Storm Tracker was thus installed and shows good mitigation for the warm biases. With the much lower costs of the sondes and the simultaneous multi-channel receiver, the Storm Tracker system has been proved to be beneficial for high-frequency observational needs in atmospheric research.

Convectively active disturbances occurring at a quasi-2-day (Q2D) interval are frequently observed over the tropical oceans from the western Pacific (WPAC;

Afternoon thunderstorms (TSs) over the Taipei metropolitan area often cause meteorological disasters. Further understanding of essential factors for TS organization is important for improving prediction accuracy. This study conducts numerical simulations in two real situations with different environmental profiles: a heavy rainfall (TS) case and a no rainfall (NoTS) case. The TS simulation reasonably captures the afternoon rainfall in the Taipei basin. The thermal structure and sea breeze evolution in the simulations are verified by the observation from a field campaign. In both cases, the sea breeze develops in the afternoon. Weak environmental flow and high humidity are observed in the TS case. In contrast, a thick and dry layer with southeasterly wind above 2-km height is presented in the NoTS case. Four idealized experiments are then performed with the initial conditions based on the actual TS/ NoTS soundings and with/without the southeasterly environmental flows. Despite the different thermal profiles, the two simulations without the southeasterly flows exhibit qualitatively similar rainfall distribution and the evolution of the sea breeze to that of the real TS simulation. However, with the southeasterly environmental flows, the simulation with the NoTS sounding exhibits considerably less convection and rainfall. Therefore, not only moisture profiles but also environmental wind profiles are critical to the TS organization. Novelly, this study further shows that the environmental flow contributes to the suppression of afternoon TSs through keeping entrainment due to the continuous supply of the dry airmass.