South China Sea Monsoon Experiment
(SCSMEX)
BMRC Dongsha Operations
Related Sites: NASA/NASDA
Tropical Rainfall Measuring Mission (TRMM)
TRMM Ground Validation Activities
SCSMEX Page (William K. Lau)
Bureau of
Meteorology, Australia
email contact : Dr. Tom Keenan
INTRODUCTION:
1.0 SCSMEX Scientific Goals
Primary Goal:
To provide a better understanding of the key physical
processes for the onset, maintenance and variability of the monsoon over Southeast Asia
and southern China leading to improved predictions.
To attain the primary goal, SCSMEX has the following specific
scientific objectives:
- To describe and document the space-time evolution
of the large scale atmospheric circulation, thermodynamic fields, as well as basic ocean
flow patterns and thermohaline structures associated with the South China Sea (SCS)
monsoon.
- To identify the influence of heating contrasts
between the South China Sea and surrounding regions and the role of the early monsoon
(April - May) convection and multi-scale processes in the SCS in the abrupt transition and
subsequent evolution of the East Asian monsoon.
- To elucidate physical processes in the oceanic
response to monsoon forcing and air-sea interaction in the South China Sea and
relationships with the adjacent oceans.
- To assess and improve the ability of regional and
global models in simulations and prediction of the monsoon onset in Southeast Asia and
southern China.
There are three components to SCSMEX:
- A pilot-phase component devoted to advanced
deployment of observation platforms for enhanced monitoring, testing of observation
strategy based on diagnostic and modeling studies.
- A field-phase component involving the set up of a
multitude of meteorological and oceanic observing platforms and satellite coverage during
intensive observation periods (IOP).
- A modelling component using a wide range of
models from regional to global scales to provide better understanding of physical
mechanisms underlying the observations and to augment the field-phase observations through
4-D data assimilation.
SCSMEX is a multi-national endeavour that is closely linked to and
coordinated with activities of national weather services and research institutions of East
Asian countries and adjacent regions as well as ongoing and planned US and international
field experiments and research programs such as the Global Energy and Water Experiment
(GEWEX) and Climate Variability (CLIVAR).
The rationale behind this plan is the upgrade to the northern part
of the existing regional scale SCSMEX observational network to provide fundamental
information relevant to mesoscale processes occurring within the region. This includes
study of the evolution of precipitating systems and their dynamics including the role of
air sea interactions in the maintenance. SCSMEX offers the opportunity to undertake these
mesoscale studies in a true oceanic monsoon environment. The observations are also of
importance to the National Aeronautics and Space Administration (NASA) Tropical Rainfall
Measuring Mission (TRMM). The observations will provide oceanic ground validation (GV) and
contribute to associated cloud modelling efforts at Goddard Space Flight Center (GSFC).
Emphasis is to be placed on further understanding issues related to cloud processes
important in retrieval problems, the role of mesoscale processes including microphysical
parameterisation and diagnosing the effects of latent heat release on the environment.
Hence the goal of the associated mesoscale program is to measure and
understand precipitation processes associated with the onset and mature phase of the South
China Sea (SCS) monsoon. The specific SCSMEX mesoscale program scientific objectives are:
1. To define the initiation, structure,
evolution and dynamics of mesoscale convective systems occurring during the onset and
mature phase of the South China Sea monsoon,
2. To obtain quantitative rainfall estimates,
vertical air motion and inferences on microphysical structure over a tropical oceanic site
within the SCSMEX primary network.
These objectives will contribute to a wide range of scientific
objectives which are of interest to SCSMEX, Global Energy and Water Cycle Experiment Asian
Monsoon Experiment (GAME) and TRMM scientists as well the following SCSMEX specific
objectives:
3. The dynamics of monsoon surges and rain
generating systems and their relationship to monsoon depressions in the SCS.
4. The characteristics of surface heat and
momentum fluxes and the role of air-sea interaction over the SCS in organizing convection
and the monsoon onset.
5. The role of SCS convection in the variability
of the East Asian jetstream and atmospheric teleconnection patterns.
6. Methods for closing the water budget of
precipitation minus evaporation as a key step toward determining the global hydrological
cycle.
A TRMM related observational enhancement to SCSMEX includes a radar
network for the following reasons:
(a) To undertake rainfall estimation studies
using start-of-the-art polarimetric radar and conventional radar techniques over an area
of 85,000 km2. This will provide improved TRMM algorithms in the oceanic regime of the
East Asia monsoon.
(b) To study convective-stratiform separation
techniques using vertical motion fields diagnosed by dual-Doppler techniques.
(c) To better understand the microphysical
structure of precipitating monsoonal systems.
(d) To provide a basis for diagnostic modeling
studies of the structure/evolution of the monsoonal systems occurring within the SCS.
2.0 SCSMEX Field Phase
The SCSMEX field phase occurred during the period 15 April to 31
August, 1998. Two Special Observing Periods (SOPs) occurred. The first SOP (SOP-1)
occurred from 5-25 May; the second SOP (SOP-2), from 5-25 June 1998.
The period whole period May-June is designated as the SCSMEX
Intensive Observing Period (IOP). An Intensive Flux Array (IFA) has been established in
the northern part of SCSMEX network.
2.1 The SCSMEX IFA Network
The SCSMEX radar network is depicted in more detail in Fig. 1. It
consists of the official SCSMEX National Oceanographic and Atmospheric Administration
(NOAA)/Tropical Oceans Global Atmosphere (TOGA) radar located on the People Republic Of
China (PRC) Shiyan #3. near 20° 22' N 116° 51' E 40-45 km south-east of Dongsha Is.
Soundings and bulk flux measurements were undertaken on the Shiyan #1 and #3
The North Central University (NCU) of Taiwan Integrated Sounding
System (ISS) was deployed at Dongsha Is located at 20° 42' N 116° 43' E along with
surface radiation measurements provided by NASA. The Bureau
of Meteorology Research Centre (BMRC) polarimetric radar C-POL also operatd on the
island of Dongsha. This offered the opportunity to employ two radars for dual-Doppler
monitoring coupled with frequent soundings, flux, radiation and rainfall measurements
within the IFA.
The IFA was augmented by an Autonomous Temperature Line Acquisition
System (ATLAS) buoy located within the southern dual Doppler lobe. This buoy measured
rainfall, surface meteorological information including fluxes and sub-surface
oceanographic temperature and salinity. It was located about 50 km from both radars in the
dual-Doppler configuration.
Aerosonde aircraft were an
additional monitoring platform undertaking routine monitoring of the low-level environment
of IFA during SOP1 and 2. Typically aerosonde monitoring will consist of:
3.0 The SCSMEX Radar Network
C-POL is a polarimetric/Doppler C-band radar and the
NOAA/TOGA radar is a C-band Doppler radar. Characteristics of these two radars are given
in Table 1. The two radar configuration was employed for
dual-Doppler and rainfall mapping studies throughout the two SCSMEX SOP's. TRMM validation
modelling studies will depend on these analyses and every attempt was made to maximise the
number of cases available for joint observation by the radars. The Shiyan #3 was on
station for SOP#1 and SOP#2. C-POL undertook observations throughout the entire IOP.
SOP#1 had rainfall measurement and TRMM GV as its
primary focus. SOP#2 was directed primarily at mesoscale studies of the evolution of
precipitations systems using dual-Doppler techniques and ancillary observations. However
during both SOP's observations relevant to these two objectives were collected.
Lack of gauge validation and meaningful disdrometer
measurements within radar range was a limitation during TOGA COARE radar studies of
oceanic convection. The SCSMEX dual-Doppler radar configuration had gauge/disdrometer
validation sites (Atlas Mooring, PRC#3 and Dongsha Is) available within 50 km of both
radars throughout the SOP#1 and SOP#2.
4.0 Some Ancillary Observations
4.1 Automatic Weather Stations
Two BMRC Automatic Weather Stations (AWS ) were
deployed on Dongsha to provide continuous information on the evolution of the surface
boundary layer flow over the island. These stations provided one min averages of
temperature, humidity, pressure, wind speed and direction and the time of each 0.2 mm
rainfall accumulation. Each unit sampled the sensors at 1 sec intervals to derive the one
min averages. The units employed an aspirated screen for the measurement of temperature
and humidity developed within BMRC. The pressure sensor employs a downward pointing static
head in the form of a 15 cm diameter circular disk. Data were recorded on site.
The AWS network operated continuously throughout
May-June 1998 and data collection was the same irrespective of IOP occurrence.
4.2 Raingauges
Four BMRC rain gauges were located on Dongsha to
provide direct estimation of rainfall over a limited area. The gauges are identical to
those employed in the BMRC AWS.
Two BMRC Joss-Waldvogel disdrometers were collocated
with the C-POL radar equipment.
Validation gauges were also located on the Shiyan #3 along with a
disdrometer.
4.3 Aerosonde
The Aerosonde is
a small, autonomous aircraft designed for operation over a range up to 10,000 km with an
in-flight duration of 4-5 days. It is being developed by ES&S Pty Ltd in a
collaborative effort with the Insitu Group in Oregon, the BMRC, CSIRO and Vaisala. An
experimental version with an operating range of 1000 km, a ceiling of 7 km and 24 h
duration was available for SCSMEX.
Navigation and winds are obtained from GPS ( position
accuracy of 100 m and wind ~1 ms-1 ) in three dimensions, and a radar altimeter
is being developed for low-altitude operations. Temperature, moisture, and pressure are
obtained by radiosonde-quality instrumentation, which is duplicated for quality checking.
Up to five aerosondes were deployed during SCSMEX.
Operational functions included monitoring the diurnal evolution of the PBL structure,
primarily over the ocean and monitoring the mesoscale structure/thermodynamic evolution of
convergent zones.
Table 1:
Characteristics of NOAA/TOGA and BMRC C-POLRadars
|
NOAA/TOGA |
BMRC C-POL |
| Peak Output Power (kW) |
250 |
250 |
| Operating Frequency (MHZ) |
5610 |
5605 |
| Pulse widths (microsec) |
0.5 and 2.0 |
1.0 and 2.0 |
| Antenna Gain (dB) |
40.3 |
45 |
| Radome loss (dB) |
0.72 dB (one way) |
Not Applicable |
| Beamwidth (degrees) |
1.55 |
1.0 |
| Max. range (km) |
600 |
600 |
| Min. range (km) |
1 |
1 |
| PRF (Hz) |
250 to 2000 |
200-1200 |
| Polarisation |
Linear Horizontal |
Linear Horizontal and
Vertical |
| Variables |
ZH,VR, V |
 ZH,VR,V,ZDR,DP, HV |
| Data system |
SIGMET IRIS |
Lassen |
Shi
Yan # 3. OPERATIONS:
This section contains links to scientific logs and data
from the Shi Yan #3. During each cruise, the TOGA radar was operated continuously by radar
scientists and engineers. Soundings were launched every six hours and surface
meteorological observations were monitored continuously. Optical rain gage, bucket gage,
and disdrometer data were also collected. A digital camera was used to document cloud
conditions and ship operations in detail.
DONGSHA OPERATIONS:
Science/operations
log, IOP#1 (5-25 May 1998)
Science/operations
log, IOP (between IOP#1 - #2)(26 May - 6 June)
Science/operations
log, IOP#2 (5-22 June)
General Scenes:
Operations Results: Radar and Cloud Scenes
IOP#1 (5-25 May 1998)
- 5 May - clouds/radar
- 6 May - clouds/radar
- 14 May - clouds/radar
- 15 May - clouds/radar
- 16 May - clouds/radar
- 9805160228.jpg
- 9805160128.jpg
- 9805160038.jpg
- 9805160330.jpg
- 9805160440.jpg
- 9805160528.jpg
- 9805160628.jpg
- 9805160728.jpg
- 9805160828.jpg
- 980516wspoutzh.jpg
- 9805160229.jpg
- waterspout9805160228.jpg
- waterspout9805160227.jpg
- waterspout9805160230.jpg
- waterspout9805160233.jpg
- waterspout9805160235.jpg
- 17 May - clouds/radar/gustfront
- 18 May - clouds/radar
- 19 May - clouds/radar
- 20 May - clouds/radar
- 21 May - clouds/radar
- 23 May - clouds/radar
- 24 May - clouds/radar
- 25 May - clouds/radar
|
Between IOP1 and IOP2 (26 May - 6 June)
|
IOP#2 (5-22 June)
|
Hourly Radar Reflectivity Plots
Movie Loops consisting of 20-24 frames, sizing from
70kb to 200kb
May
June
| 
