Masaki Katsumata

Mismo field experiment in the equatorial Indian Ocean

The Mirai Indian Ocean cruise for the Study of the Madden-Julian oscillation (MJO)-convection Onset (MISMO) was a field experiment that took place in the central equatorial Indian Ocean during October–December 2006, using the research vessel Mirai, a moored buoy array, and landbased sites at the Maldive Islands. The aim of MISMO was to capture atmospheric and oceanic features in the equatorial Indian Ocean when convection in the MJO was initiated. This article describes details of the experiment as well as some selected early results. Intensive observations using Doppler radar, radiosonde, surface meteorological measurements, and other instruments were conducted at 0°, 80.5°E, after deploying an array of surface and subsurface moorings around this site. The Mirai stayed within this buoy array area from 24 October through 25 November. After a period of stationary observations, underway meteorological measurements were continued from the Maldives to the eastern Indian Ocean in early December. All observatio...

Quality-Controlled Upper-Air Sounding Dataset for DYNAMO/CINDY/AMIE: Development and Corrections

AbstractThe 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 ...

Sounding-Based Thermodynamic Budgets for DYNAMO

The Dynamics of the Madden‐Julian Oscillation (DYNAMO) field campaign, conducted over the Indian Ocean from October 2011 to March 2012, was designed to study the initiation of the Madden‐Julian oscillation (MJO). Two prominent MJOs occurred in the experimental domain during the special observing period in October and November. Data from a northern and a southern sounding array (NSA and SSA, respectively) have been used to investigate the apparent heat sources and sinks (Q1 and Q2) and radiative heating rates QR throughout the life cycles of the two MJO events. The MJO signal was far stronger in the NSA than the SSA. Time series of Q1, Q2, and the vertical eddy flux of moist static energy reveal an evolution of cloud systems for both MJOs consistent with prior studies: shallow, nonprecipitating cumulus during the suppressed phase, followed by cumulus congestus, then deep convection during the active phase, and finally stratiform precipitation. However, the duration of these phases was shorter for the November MJO than for the October event. The profiles of Q1 and Q2 for the two arrays indicate a greater stratiform rain fraction for the NSA than the SSA—a finding supported by TRMM measurements. Surface rainfall rates and net tropospheric QR determined as residuals from the budgets show good agreement with satellite-based estimates. The cloud radiative forcing was approximately 20% of the column-integrated convective heating and of the same amplitude as the normalized gross moist stability, leaving open the possibility of radiative‐ convective instability for the two MJOs.

MJO Signals in Latent Heating: Results from TRMM Retrievals

Abstract Four Tropical Rainfall Measuring Mission (TRMM) datasets of latent heating were diagnosed for signals in the Madden–Julian oscillation (MJO). In all four datasets, vertical structures of latent heating are dominated by two components—one deep with its peak above the melting level and one shallow with its peak below. Profiles of the two components are nearly ubiquitous in longitude, allowing a separation of the vertical and zonal/temporal variations when the latitudinal dependence is not considered. All four datasets exhibit robust MJO spectral signals in the deep component as eastward propagating spectral peaks centered at a period of 50 days and zonal wavenumber 1, well distinguished from lower- and higher-frequency power and much stronger than the corresponding westward power. The shallow component shows similar but slightly less robust MJO spectral peaks. MJO signals were further extracted from a combination of bandpass (30–90 day) filtered deep and shallow components. Largest amplitudes of bo...

Estimates of Tropical Diabatic Heating Profiles: Commonalities and Uncertainties

This study aims to evaluate the consistency and discrepancies in estimates of diabatic heating profiles associated with precipitation based on satellite observations and microphysics and those derived from the thermodynamics of the large-scale environment. It presents a survey of diabatic heating profile estimates from four Tropical Rainfall Measuring Mission (TRMM) products, four global reanalyses, and in situ sounding measurements from eight field campaigns at various tropical locations. Common in most of the estimates are the following: (i) bottom-heavy profiles, ubiquitous over the oceans, are associated with relatively low rain rates, while top-heavy profiles are generally associated with high rain rates; (ii) temporal variability of latent heating profiles is dominated by two modes, a deep mode with a peak in the upper troposphere and a shallow mode with a low-level peak; and (iii) the structure of the deep modes is almost the same in different estimates and different regions in the tropics. The primary uncertainty is in the amount of shallow heating over the tropical oceans, which differs substantially among the estimates.

Observed Synoptic-Scale Variability during the Developing Phase of an ISO over the Indian Ocean during MISMO

A case study of an intraseasonal oscillation (ISO) is investigated in the period leading up to its convectively active phase during the Mirai Indian Ocean Cruise for the Study of the MJO-Convection Onset (MISMO), which was conducted during boreal autumn 2006. Detailed observations, including apparent heat and moistureanalyses,revealthatsynoptic-scalevariabilityofheatandmoisturesourcesandsinksassociatedwith the passage of three eastward-propagating cloud systems (EPCSs) was prominent during this period. These systems with periods of ;6 days propagated through the MISMO domain, priming the atmosphere for a convectively active phase of the ISO. The prominent shallow heating during this period may explain the ratherslow(8 m s 21 )propagationspeedforEPCSs.Thezonalstructureandsignofthefrictionalconvergence show that these EPCSs have common characteristics to the frictional Kelvin mode studied by Ohuchi and Yamasaki. With the analyses of the period-averaged vertical profiles, the EPCSs were identified as the principal mechanism to moisten the atmosphere prior to the ISO convectively active phase.

The Response of 36- and 89-GHz Microwave Channels to Convective Snow Clouds over Ocean: Observation and Modeling

Abstract The first study in both observing and modeling radiative properties of snow clouds in the microwave frequencies is described in this paper. Snow clouds over ocean were observed simultaneously using an airborne microwave radiometer and an X-band Doppler radar. Results show that brightness temperatures at 36- and 89-GHz microwave channels responded well to the horizontal variations of precipitation particles and to the cloud dynamic structures determined by the Doppler radar, which reflect the development stages of convective cells. For the quantitative validation, physical retrievals of liquid water and snow water amounts were performed using a radiative transfer model. The retrieved snow water amount agrees well with the observed snow water amount that was converted from observed radar reflectivity. In the retrieval method, the model-simulated brightness temperatures were able to match the observed values within 3 K per channel for the most part. The ambiguities of the retrieved parameters that d...

Observation of Moisture Tendencies Related to Shallow Convection

AbstractTropospheric moisture is a key factor controlling the global climate and its variability. For instance, moistening of the lower troposphere is necessary to trigger the convective phase of a Madden–Julian oscillation (MJO). However, the relative importance of the processes controlling this moistening has yet to be quantified. Among these processes, the importance of the moistening by shallow convection is still debated. The authors use high-frequency observations of humidity and convection from the Research Vessel (R/V) Mirai that was located in the Indian Ocean ITCZ during the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the MJO (CINDY/DYNAMO) campaign. This study is an initial attempt to directly link shallow convection to moisture variations within the lowest 4 km of the atmosphere from the convective scale to the mesoscale. Within a few tens of minutes and near shallow convection occurrences, moisture anomalies of 0.25–0.5 g kg−1 that correspond to tendencies on ...

Observations of a Super Cloud Cluster Accompanied by Synoptic-Scale Eastward-Propagating Precipitating Systems over the Indian Ocean

The multiscale structure of a super cloud cluster (SCC) over the equatorial Indian Ocean, observed in November and December 2006, was investigated using data from satellite microwave sensors and surfacebased radars. The smaller-scale structure of this SCC was marked by a complicated relationship between rainfall systems and upper-tropospheric cloud shields, which moved eastward and westward, respectively, with a cycle of 2‐4 days. In the analyses, attention was given to the structure of slow eastward-propagating (5‐11 m s 21 ) precipitating systems and related synoptic-scale (;2000 km) disturbances. A case study of one of the systems revealed that it consisted of several lines of convective cells with a depth that was usually shallower than 10 km unless the cells encountered the westward-moving cloud shields. The environment of the convective lines was characterized by persistent unstable conditions with an increase of the westerly flow in the lower troposphere, suggesting the existence of a synoptic-scale upward motion. Composite analyses revealed that each rainfall system formed in a region of zonal flow convergence near the surface and divergence near 300 hPa. The vertical temperature structure tilted westward with height below this pressure level and eastward aloft, similar to that of a convectively coupled Kelvin wave. These results suggest that a SCC involves a group of synoptic-scale shallow waves propagating eastward. An additional analysis over the western Pacific also showed the predominance of eastward propagation in a SCC, demonstrating the advantage of satellite microwave sensors over infrared ones in monitoring the multiscale structure of tropical convection.

Latitudinal distribution of aerosols and clouds in the western Pacific observed with a lidar on board the Research Vessel Mirai

We observed vertical distributions of aerosols and clouds with a lidar on board R/V Mirai and analyzed latitudinal features using the data of four cruises in the western Pacific. According to the measured backscattering coefficient, aerosol density was generally high at latitudes above 25° N where the westerly from the Asian continent prevailed. The wavelength dependence of the retrieved aerosol backscattering showed that the characteristics of aerosols in the continental air mass were clearly different from those at lower latitudes. Aerosol concentration in the boundary layer varied significantly in the lower latitudes and was correlated with surface wind speed. The wavelength dependence of aerosol backscattering indicated that aerosol particles were larger when surface wind speed was high.