Outline and Objectives of LAPS
Kenji Nakamura
Hydrospheric Atmospheric Research Center, Nagoya University
1. Introduction
Recently, the role of the atmospheric boundary layer on the onset of precipitation
attracts attention. Model studies suggest that the precipitation system will be triggeredby large thermal eddies in the atmospheric boundary layer. The mechanism to trigger
precipitation systems may be different in dry season and wet season. To clarify themechanism we proposed a project the “Lower Atmosphere and Precipitation Study(LAPS) as one of the CREST/JST projects and fortunately our proposal was accepted.
This implementation document is prepared for the LAPS.
The LAPS consists of (1) field experiments, (2) model simulation and (3) large scale dataanalysis. The first one (field experiment) focuses on the planetary boundary layer
observations from ground to above the boundary layer, in other words, full ABL. To meetthe objectives, several instruments will be deployed: a lower atmosphere windprofiler
radar, Doppler sodars, a flux tower, etc. The main observation site is expected in theHUBEX area in China, where we have a dry season in winter and wet season insummer. One of other field experimental site is Miyakojima Island area which is in thesouth-west island chain in Japan. We plan to have the aerosonde operation along with aflux tower monitoring and enhanced radiosonde observations. The last site is theCommunications Research Laboratory’s (CRL’s) Okinawa observatory where CRL
established an ideal atmosphere observation base which has a 400 MHz windprofiler
radar, an L-band windprofiler radar, a polarization Doppler radar with bi-static
reception system and others.
2. ObjectivesThe objective of LAPS is to improve our understanding on the role of the atmosphericboundary layer on the onset of precipitation system in dry and wet season.
The land-atmosphere interaction occurs through the atmospheric boundary layer.
Exchanges of momentum, sensible heat energy, latent heat energy, water, trace gases,etc. occur between land and atmosphere. Near surface measurements, for example,
using obseravation towers, are commonly performed. However, free atmosphere is 1 – 2

km above the surface, and current atmospheric boundary layer observation is notenough for the study on the exchange of energy and water between land surface andfree atmosphere. One of the vigorous and important manifestation of theland-atmosphere interaction is the precipitation. Atmospheric stability, verticaltransport as well as lateral transport of water vapor are important for the onset andmaintaining of the precipitation system. Atmospheric boundary layer strongly controls
the vertical transport of energy and water vapor and the stability. The atmosphericboundary layer could also be affected by the precipitation via radiation, water flux tothe surface, etc. The objectives of LAPS is to understand the role of the atmosphericboundary layer for the onset of precipitation system and the counter effect to land
surface. After understanding of these mechanism, the role of the atmospheric boundary
layer for the migration and recession of the wet region over land will be understood.
Recent observational studies revealed that the precipitation system in the east Asia isdifferent from those in U.S. The precipitation system in east Asia is characterized bydeep wet atmosphere. When deep wet atmosphere exists, the rain systems are relatively
low compared with those of U.S. The wet region migration seems to be associated withthe deep wet atmosphere migration over land. Satellite data analysis in sub-tropicalregion shows that deep rain systems likely occur between wet and dry regions. Thisfinding is in accordance with the ground-based observational results. However, thesatellite data does not always show the same phenomena in the mid-latitude region.
Generally speaking, the atmosphere in the tropical region is quiet. In other words, thedisturbances are weak, and the wind are also weak. In this situation, local phenomena
appear more clearly. On the other hand, mid-latitude region, baroclinic disturbances isvigorous and the wind is generally strong. There, synoptic scale disturbances and local
scale disturbances interaction becomes more important. The atmospheric boundary
layer effect may be in the category of local scale phenomena. The difference of theboundary layer effect of the atmospheric boundary layer between tropical region andmid-latitude region should also be studied.
The research contents could be expressed in phases as:(1) To study wet and try region interaction over land in terms of land-atmosphereinteraction, and(2) Precipitation system with Asian tastes.
Working hypotheses are important to focus the research points and specify the issues.

According to satellite data analysis and others we may have working hypotheses asfollows.
(1) There exist patchy wet areas in the wet/dry transition regions.
(2) Cloud and precipitation system transports water vapor in ABL to middle layer andmoistens there.
(3) Turbulent structure ABL determines the onset of precipitation system.
(4) ABL strongly affects the diurnal variation of precipitation even in mid-latitude
regions.
(5) Diurnal variation of precipitation system enhances high precipitation systems andtransport moisture into upper layers.
(6) Humid middle layer is essential for full development of precipitation system.
(7) Dry middle layer suppresses shallow convection but enhances deep convections.
(8) High precipitation system likely exists in the boundary layer of dry and wet regions.
(9) When the land is sufficiently wet, the precipitation system becomes more likely
ocean type.
(10) A high and strong precipitation layer is maintained by a feedback system. When thefeedback system is broken, another regime appears.
(11) Migration of wet region needs sufficient moist air and wet soil.
(12) Precipitation system in China takes an essential role in the rain over Japan.
3. Team structure
We have three groups in LAPS: (1) ABL study group, (2) Precipitation study group and(3) ABL modelling group,and (4)Large scale analysis group. ABL study group. The
members are actually overlapping. For the field experiment, the ABL and Precipitationgroup would tightly collaborate. The modeling group would utilize the observation data
and also suggest suitable observation strategy, vice versa
4. Schedule
The project will hopefully continue for full five years. Big efforts will be put to the field
experiments, and the first one or two years would be spent for the preparation for thefield experiment. Data analysis of satellites, re-analysis data, etc. and the model studies
will be conducted parallelly.