AUSTRALIA - JAPAN SYMPOSIUM
AUSTRALIA - JAPAN SYMPOSIUM ON EARTH SYSTEMS SCIENCE
AND ON NANOMATERIALS
Canberra, 21 November 2006
Tropical rain characteristics in models and satellite observations
Dr Yukari Takayabu, Associate Professor, Center for Climate System Research, University of
Tokyo, Japan
Dr Takayabu is interested in the tropical cloud and precipitation systems and their coupling with the large-scale
atmospheric disturbances and their link to the atmosphere-ocean interactions and to the global climate. Her
researches have been based on the satellite data, field experiment data, and recently on the climate modelling
data. Early studies utilised Japanese GMS data to derive the convectively coupled equatorial waves. Her
first visit of Australia was to Townsville in 1992 to observe the field campaign of the Tropical Ocean Global
Atmosphere-Coupled Ocean Atmosphere Response Experiment (TOGA-COARE). Recent studies are about
the tropical intraseasonal oscillation (MJO) and tropical precipitation characteristics utilizing TRMM satellite
data. This year, she also joined the field experiment utilizing R/V Mirai over the Indian Ocean to detect the
triggering of MJO convection. In the near future, she expects to utilize the CloudSAT data to analyze the
three-dimensional cloud data to understand how cloud-and-precipitation systems influence the atmosphere
dynamically and through radiation.
First, a study to characterise the tropical precipitation systems observed from space is introduced. Among them, the Rain-yields Per Flash (RPF) over the entire tropics were calculated from 3 years of data collected by a Lightning Imaging Sensor (LIS) and a Precipitation Radar (PR) housed onboard the Tropical Rainfall Measuring Mission (TRMM) satellite. The results confirm that RPF is a reliable indicator of precipitation regimes, with a marked land (average 3.94 x 108 kg fl-1)-ocean (1.96 x 109 kg fl-1) contrast. A large seasonal variation of RPF values over monsoonal regions is observed, and there is a transition zone with intermediate values over coastal oceans. A good correlation between RPF and the Tall Convective Rain Contribution was found especially over land. This result indicates that large amounts of tall convective rain are fundamentally associated with intense updrafts that are able to sustain vigorous lightning activity. The correlation is weaker over ocean, except for the transition zone over coastal oceans. RPF properties in the Madden-Julian Oscillation (MJO, or the tropical intraseasonal oscillation), and in the tropical cyclones are also discussed.
Secondly, diurnally marching precipitation properties over land and over coastal oceans in an atmospheric general circulation model used in the Japanese climate model MIROC, are evaluated with the TRMM data. An implementation of the relative humidity threshold scheme to the prognostic Arakawa-Schubert convective parameterization improves the performance of the diurnal march of the precipitation. It is suggested that the coastal transition zone observed with the above RPF values consists of these diurnally marching precipitation systems.
At last, some results of cloud and precipitation simulations with a Japanese global cloud resolving model, named as the Nonhydrostatic ICosahedral Atmospheric Model (NICAM), run with the Earth Simulator will be introduced.
