Miki Hattori

Observing-System Research and Ensemble Data Assimilation at JAMSTEC

Recent activities on ensemble data assimilation and its application to observing-system research at the Japan Agency for Marine-Earth Science and Technology are reviewed. A revised version of an ensemble-based data assimilation system for global atmospheric data has been developed on the second-generation Earth Simulator. This system assimilates conventional atmospheric observations and satellite-based wind data into an atmospheric general circulation model using the local ensemble transform Kalman filter (LETKF), a deterministic ensemble Kalman filter algorithm that is extremely efficient with parallel computer architecture. The updated system incorporates improvements to the previous system in the forecast model, data assimilation algorithm and input data. Using the LETKF system, observations taken during field campaigns are evaluated by data assimilation experiments involving adding or removing observations. The results of these observing-system experiments successfully demonstrate the value of the observations and are highly useful for exploring the predictability of atmospheric disturbances.

Meridional march of diurnal rainfall over Jakarta, Indonesia, observed with a C-band Doppler radar: an overview of the HARIMAU2010 campaign

AbstractThis paper presents an overview of the HARIMAU2010 campaign focusing on convective activity with the diurnal rainfall meridional march (DRMM) over Jakarta, which is located on the northern coast of Jawa Island of the Indonesian maritime continent (IMC), based on 1-month intensive observations by a C-band Doppler radar and multi-point atmospheric sounding array conducted during 16 January–14 February 2010. The campaign period corresponded to a phase after large-scale Madden–Julian oscillation (MJO) active convections passed over Jakarta (MJO inactive phase). The cross-equatorial northerly surge (CENS) intruded into the Jawa Sea with a cold tongue (CT) of sea surface temperature (SST) in the beginning of the period (CENS active period: 16–26 January), and then, it started to retreat (transition period: 27 January–05 February); afterward, only a few signs of it were apparent (CENS inactive period: 06–14 February). The observational results showed that (1) rainfall over Jakarta has the nature of DRMM during the MJO inactive phase at least, (2) the DRMM is likely driven primarily by “land-breeze”-like local meridional circulation, and (3) the meridional spatiotemporal variation of rainfall over Jakarta is thus controlled by activities of both the CENS and CT over the Jawa Sea.

Diurnal cycle over a coastal area of the Maritime Continent as derived by special networked soundings over Jakarta during HARIMAU2010

AbstractThis study investigates the nature and mechanisms of the diurnal precipitation system over a coastal area of the Maritime Continent (MC) by utilizing the data from a field campaign, HARIMAU2010. During the 1-month campaign, diurnal cycles over Jakarta were well identified by special networked soundings and a C-band radar. Radar and satellites captured the convective-type heavy rains that appeared in the afternoon over the array, which were followed by stratiform-type precipitation during the night. Thermodynamic budget analyses were also performed using sounding data. The period-averaged vertical profiles of Q1 and Q2 indicate that diurnal precipitation acted as deep convection in the diabatic heating and drying. The diurnal composite of the obtained parameters revealed key processes such as (1) just before the onset of the afternoon convective rain, the lower troposphere was moistened by subarray-scale processes; (2) moistening of the troposphere continued during the convective heavy precipitation; (3) the stratiform rains during the night were partly maintained by consuming the pre-existing hydrometeor aloft; and (4) in the early morning, the clouds redeveloped over the ocean to produce precipitation as well as hydrometeor aloft. The possible physical processes promoting lower-tropospheric moistening before onset of the convective rain are also discussed.

Cold surge event observed by radiosonde observation from the research vessel “Hakuho-maru” over the Philippine Sea in December 2012

AbstractThe thermal energy transfer from the sea surface to the atmosphere associated with a cold surge event was investigated with observations from radiosondes on the research vessel “Hakuho-maru” over the Philippine Sea in December 2012. These observations were analyzed, and the results were compared with those obtained from observations over the East China Sea in the Air Mass Transformation Experiment in 1974 (AMTEX ‘74). The horizontal advection of cold and dry air associated with the cold surge dominated at heights below 850 hPa. In spite of this strong advection, the local temporal variations in the temperature and moisture were small, because the advection was balanced by the transfer of heat and moisture from the sea surface, which is qualitatively the same behavior as observed during the cold surge event in AMTEX ‘74. The eddy transport of the total heat energy from the sea surface to the atmosphere was estimated at about 410 W/m2, which is about half of the maximum value of 780 W/m2 observed during AMTEX ‘74. This result shows the existence of considerable heat transfer from the sea surface to the atmosphere over the Philippine Sea, which is the downstream region of the cold surge, after it passed through the East China Sea.