Thermodynamical interpretations of generation and decay of stable layers over the Indochina Peninsula in the dry season
Masato I. Nodzu (1), Shin-Ya Ogino (1), Yoshihiro Tachibana (3), Manabu D. Yamanaka (1)
(1) Kobe University
(3) Tokai University
1. Introduction
We have investigated seasonal variations of the atmospheric stability
in the lower troposphere and their mechanisms in order to understand
the role of the strong stable layer seen in the lower troposphere in the
dry season. We have shown that strong stable layers frequently
appear at a height of about 2 km in the early dry season and that
their mean height increases up to about 5 km and become weak in the
late dry season as a climatological characteristic. We have also
shown that intermittent appearances of generation and decay of
stable layers with a time scale from ten to fifty days dominate in
a seasonal advance of each year (Nodzu et al., 2004, submitted to
J. Climate). In this paper, we investigate the generation and decay
mechanisms of stable layers with the intraseasonal time scale in
terms of thermodynamics.
2. Data
NCEP/DOE AMIP-II reanalysis data (http://wesley.wwb.noaa.gov/reanalysis2/)
are utilized in the thermal and moisture budget analysis. The budget
is calculated over the triangle region in the western inland of the
Indochina Peninsula which includes six grid points (20 N, 100 E),
(17.5 N, 100 E), (15 N, 100 E), (17.5 N, 102.5 E), (15 N, 102.5 E),
(15 N, 105 E) ). The analysis duration is from October 1999 to May 2000.
3. Results
First, we describe an example of generation and decay of stable
layers. During the period from 11 to 25 April 2000, just before the
onset of rainy season, a stable layer was generated around a height
of 500 hPa and decayed. When it was generated, increase of the
potential temperature above 500 hPa dominated and the potential
temperature change below 500 hPa was not significant. On the other
hand, when it was decayed, relatively large increase of the
potential temperature was recognized below 500 hPa. It is found
that the heating above 500 hPa during the stable layer generation
was caused by the horizontal warm advection and that the heating
below 500 hPa during the decay was caused by the horizontal warm
advection and the Q_1 (apparent heat source). It is inferred from a
comparison of temporal and spatial variations of Q_1 and Q_2 that
the heating by Q_1 below 500 hPa during the decay was mainly caused
by the release of latent heat. In this example, therefore, the
stable layer is considered to have been generated by the upper
horizontal warm advection and decayed by the lower horizontal warm
advection and the latent heat release.
4. Summary
The thermodynamical interpretation of generation and decay
mechanisms were performed on intraseasonal variations of stable
layers over the Indochina Peninsula in the dry season from
1999 to 2000 by the thermal and moisture budget analysis.
We did not find a common particular mechanism explaining all the
generation and decay processes. However, we also found a weak
tendency that a specific mechanism becomes important in the
early dry season. These findings will be confirmed by expanding
the analysis duration into twenty-five dry seasons from 1979 to 2004.
Submittal Information
Name :
Date :
Masato I. Nodzu
09-Aug-04-15:44:08
Organization :
Theme :
Kobe University
Theme 3
Address :
Presentation :
Graduate School of Science and Technology, 1-1 Rokkodai-chou, Nada, Kobe 657 8501, Japan