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12A1 the Tropical Warm Pool International Cloud Experiment (TWP-ICE)

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12A1 the Tropical Warm Pool International Cloud Experiment (TWP-ICE) 12A1 The Tropical Warm Pool International Cloud Experiment (TWP-ICE) Peter T. May1, James H. Mather2, Geraint Vaughan3, Christian Jakob1, Greg M. McFarquhar4, Keith N. Bower3, and Gerald G. Mace5 1 Bureau of Meteorology Research Centre, Melbourne, Australia 2. Pacific Northwest National Laboratory, Richland, Washington, USA 3. School of Earth, Atmospheric and Environmental Sciences, University of Manchester, UK 4. Department of Atmospheric Sciences, University of Illinois, Illinois, USA 5. Meteorology Department, University of Utah, Utah, USA physical and chemical properties of cirrus and 1. Introduction the upper troposphere region. A crucial factor for our ability to forecast future The experiment was designed to provide a climate change is a better representation of comprehensive data set for the development of tropical convection and clouds in climate cloud remote sensing retrievals and initialising models. This requires a better understanding of and verifying a range of process-scale models, the multi-scale factors that control tropical with a view to improving the parameterisation convection as well as an improved of tropical convection and clouds in numerical understanding of how the characteristics of the weather prediction and climate models. convection affect the density and nature of the Accordingly, a surface measurement network cloud particles that are found in deep (including a research ship) of unprecedented convective anvils and tropical cirrus. Deep coverage for a tropical experiment was convection also lifts boundary-layer air into the combined with a fleet of five research aircraft to Tropical Tropopause Layer (TTL), affecting the enable in-situ and remote-sensing composition of this region and through it the measurements of clouds, meteorological global stratosphere. Understanding the variables and composition from the ground into transport of gases and particles in deep the lower stratosphere. convection is also therefore of global importance. As a response to this challenge, a A major motivation for choosing the Darwin major field experiment named the Tropical area as the experiment location is that it Warm Pool International Cloud Experiment samples a wide variety of convective systems, (TWP-ICE), including the UK ACTIVE (Aerosol including those typical for a monsoon coastal and Chemical Transport In tropical conVEction) environment, similar to those experienced by consortium, was undertaken in the Darwin, large populations under the influence of the Northern Australia area in January and Asian and Indian monsoons. Monsoon cloud February 2006. The overall goals of the systems are typically oceanic and the lessons experiment were to observe the evolution of the of TWPICE will be applied across tropical cloud systems, their environmental controls oceanic areas including the InterTropical and their impacts from the initial convective Convergence Zone (ITCZ). The monsoon has cells through to the decaying and self- very high intra-seasonal variability (e.g. maintaining cirrus, including their impact on Drosdowsky, 1996), and experiences both upper tropospheric composition. TWP-ICE active periods with storms typical of a maritime builds on such experiments as the Tropical environment and “breaks” when the storm Ocean Global Atmosphere Coupled Ocean systems are characteristic of coastal and Atmosphere Response experiment (TOGA- continental areas. These break storms have COARE; Webster and Lukas, 1992) and the high lightning activity and are often isolated, Central Equatorial Pacific Ocean Experiment forming on sea breezes and other local (CEPEX; http://www-c4.ucsd.edu/cepex; circulations, although some of these ultimately Heymsfield and McFarquhar, 1996) that develop into squall lines. This is in contrast to focused on air-sea interactions along with their the widespread, but generally weaker impact on convection and convectively convective activity sampled during the active generated cirrus respectively. Cloud sampling phase of the monsoon (e.g. Mapes and Houze, strategies employed during TWP-ICE built on 1992; Keenan and Carbone, 1992; May and previous experiments such as the Cirrus Ballinger, 2007). The TWPICE period sampled Regional Study of Tropical Anvils and Cirrus both these regimes as well as a relatively Layers - Florida Area Cirrus Experiment suppressed period with storms of only (CRYSTAL-FACE; Garrett et al., 2005; moderate vertical extent. Heymsfield et al., 2005) which emphasized the Another important feature that makes Darwin the ideal site for studying tropical convection is 1 that it boasts what is probably the most cloud-resolving models and evaluation of their comprehensive long term meteorological predictions. These measurements followed on observational network anywhere in the tropics. from those made by ACTIVE in the pre- This includes research polarimetric radar, Christmas campaign, as described in the Doppler weather radar, wind profilers, a companion paper (Vaughan et al 2006), and to radiosonde station, the Australian Bureau of document the evolution of the atmosphere from Meteorology (hereafter, referred to as the one with substantial impact from biomass Bureau) operational mesonet and the Darwin burning at the end of the dry season to pristine Atmospheric Radiation Measurement (ARM) conditions in late January. Climate Research Facility (ACRF) site operated by the US Department of Energy. These systems all provide long term data sets so that 2. Ground Network Observations the TWPICE data can be put into a climatological context. One of the cornerstones of TWP-ICE was an extensive ground-based observational network The combination of excellent facilities and the that included long-term components as well as range of tropical weather experienced has instruments deployed specifically for the made for a long history of field programs in the campaign. The network spanned a region with Darwin area. Important examples of these a radius of approximately 150 km, centred on were the combined AMEX/EMEX/STEP Darwin. The long-term component included (Australian Monsoon Experiment / Equatorial Bureau instrumentation associated with both Monsooon Experiment / Stratopshere- meteorological research and operational Troposphere Exchange Program) programs in forecasting applications (Keenan and Manton, the late 1980s focussing on the structure of the 1996), as well as a DOE Atmospheric Cloud Australian monsoon and the potential impact and Radiation Facility (ACRF) site (Ackerman on troposphere/stratosphere transport (e.g. and Stokes, 2003). Additional instrumentation Keenan et al., 1989; Mapes and Houze, 1992; deployed for the campaign included a network Russell et al., 1993), the Maritime Continent of radiosonde sites, surface energy flux Thunderstorm Experiment (MCTEX) focussing systems, radar wind and cloud profilers, on the evolution of intense island based multichannel microwave instruments, two thunderstorms (Keenan et al, 2000), the Darwin AERIs, ocean observations and a lightning Waves Experiment focussing on convectively detection network. Figure 1 illustrates the TWP- generated gravity waves (Hamilton et al., 2004) ICE/ACTIVE campaign region including the and the Emerald experiment focussing on location of some of these observation cirrus measurements around deep intense elements. This instrument network served storms (Whiteway et al, 2004) . multiple purposes: it provided detailed information about the meteorological The science goals of the experiment are listed environment which was critical for mission flight in Table 1. A general theme was to document planning and will be important for measurement in as much detail as possible the evolution of interpretation; it provided detailed information the cloud systems, the environmental controls about the vertical distribution of cloud on this evolution and their impact on the properties, a major focus of the campaign; and environment. Another important component it provided boundary conditions for the was to provide data for the validation of ground experiment domain to aid in post-experiment and space borne remotely sensed cloud model simulations of the campaign. properties as these tie the experiment into long-term observational data sets in the tropics The Bureau operates an extensive suite of (e.g Ackerman and Stokes, 2003). The main instrumentation in the Darwin region. Bureau focus of activities was within a ring of observation assets in this region are listed in radiosonde stations established around Darwin Table 2. These include two weather radar for the experiment although survey aircraft systems, a radiosonde launch site, wind missions were conducted to measure the large profilers and a network of Automated Weather scale aerosol and chemical composition of the Stations (AWS). These instruments provide a region and to sample highly aged cirrus (clouds long-term baseline for meteorological separated from their parent convection more conditions in the Darwin region and a detailed than 24 hours) when the centre of deep description of the region during the campaign. convection was located well to the south. Of particular interest for the experiment are the two weather radars. One is fully polarimetric A key goal of the research being conducted (Keenan et al., 1998) and the other is an with TWPICE data is to understand the link operational Doppler system. They have a between the strength and organisation of the baseline of approximately 25 km and have a parent convection, the properties of the aerosol dual-Doppler lobe over the open ocean.
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