GEWEX-iLEAPS Conference (2009-08-24..28, Melbourne, Australia) [Memo by Kooiti Masuda, written 2009-08-28, minor edit 2009-09-02] [This is not a report of the session, but just my summaries of individual presentations.]
[The presenters' names are mentioned, but not the co-authors'.]
Based on quasi-isentropic back trajectory with NCEP-DoE Reanalysis 2, much of the source of summer floods in the Mississippi river basin such as of 1993 and 2008 was found to be in the Caribbean Sea. Droughts and floods there are not simple mirror image. Both of those case accompany below-average recycling of water in the atmosphere over the continent and drought condition over the southwest US.
Quantitative diagnosis of the hypothesis that Madden-Julian Oscillation (MJO) modulates tropical cyclones (TCs) is made. MJO is represented by Wheeler-Hendon MJO index based on outgoing longwave radiation and lower tropospheric winds. TC is quantified by Emanuel's GPI with NCEP-NCAR Reanalysis data. Modulation of GPI by MJO is clearly seen, but somewhat less clear than modulation of the number of TCs by MJO. Among the factors entering the construction of GPI, relative humidity in the mid-troposphere is the most important.
To understand how the humidity in the tropical tropopause transition layer (TTL) is determined, idealized simulations with a cloud-resolving model (WRF) are made. The initial condition is based no experimental observations of TWP-ICE (Tropical Warm Pool International Cloud Experiment, Jan.-Feb. 2006 around Darwin), and the TTL is assumed to be sub-saturated in one case and super-saturated in another. Microphysics plays an important role in determining humidity in the lower part of TTL. Ice particles grow at the expense of water vapour. In the moist case, water is supplied as ice from below.
TRMM Multi-satellite precipitation analysis (TMPA) is a near-global precipitation data set covering 1998 to recent. Temporal and spatial resolution is 3-hourly and 0.25 degrees lat./long. Microwave data are inter-calibrated, and augmented with infrared data which have been calibrated with microwave data. The fields are rescaled with the monthly gauge-satellite composite.
Climate-oriented extreme indices are computed with TMPA.
The statistics based on TMPA differs from those provided by ETCCDI [joint CCI/CLIVAR/JCOMM Expert Team on Climate Change Detection and Indices] which are based on station data at some locations (e.g. Bhutan) where the topography is complex and GPCP does not have gauge observations.
The spatial distribution of R95pTOT is generally similar to that of PRCPTOT, but there are some different features. R95pTOT is larger in northwest Australia, Mexico and the la Plata basin, and smaller in Amazon basin and the South Pacific Convergence Zone, than proportional to total precipitation.
Cloud regimes are defined in Jakob and Tselioudis (2003, GRL) based on ISCCP (International Satellite Cloud Climatology Project) D1 data which contains counts sorted by cloud top pressure and cloud optical thickness in 280 km grid boxes.
TRMM latent heating is composited by ISCCP regimes. The profile of CC and MIX regimes resemble classical convection profiles, while that of CD regime has a stronger peak at a higher position. In the tropical Pacific, most cases are CD and MIX.
To assess how the convection changes in a warming world, the relationship between the frequencies of convective cases and the sea surface temperature (SST) anomalies are analyzed. "Cool period" 1985-1989 and "warm period" 2002-2006 are compared. The distribution of convective regimes do not change so much, but the CD regime is much expanded in warm period. Also, time series are analyzed by separating in seasonal, interannual and long-term time scales. In the seasonal and interannual time scales, all convective types are more frequent when SST is high. In the long-term, the relationship is more complicated, and the CD type (stronger convection) is more frequent when SST is high.
The Tonle Sap Lake becomes a vast shallow water body in post-monsoon season. Precipitation occurs in the morning. Its cause is examined by experiments with a numerical model (ARPS).
In the simulation, convective band (northwest to southeast) appears at the west side of the lake before the land breeze from the east coast has not reached the lake. The feature is reproduced even if the mountain topography is removed, If the specified lake surface temperature is lower than actual, the feature is not reproduced though daytime lake breeze appears. Accordingly, the main cause is neither low-level convergence of land breezes nor descent of radiatively cooled air from the mountain slope. It should be some thermal contrast between the lake and the surrounding land.
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