Chapter 4

Experimental Design

What follows should be considered an overview of the experimental design. A more detailed plan will be submitted at the time of the proposal, based on favorable review of this white paper.

Year of Experiment and Domain

We are aiming for about a 4 month experiment between January and April of 1998. The ideal location is the central equatorial Indian Ocean between about 55šE and 90šE and between 15šN and 15šS as depicted on the front cover. Male (3.5°N, 73°E), an island of Maldives, is the tentative choice for the experimental base, due to its proximity to the domain of interest.

Experimental Design

The conceptual picture as shown in Figure 5 will guide the design of the experiment. There are five atmospheric reservoirs in INDOEX. In each of these, specific issues will be addressed.

1. Cloud-free area in the Arabian Sea: direct solar and IR forcing in cloud-free area off the coast to observe the evolution (aging) of the Indian plume.

2. Cloud-topped marine boundary layer north of the ITCZ: indirect forcing due to increase in CCN resulting from the aerosol-rich continental air.

3. Polluted convective clouds in the ITCZ: vertical cloud processing of aerosols; release of greenhouse gases; release of particulate matter into the tropopause region; water vapor and ozone greenhouse effect and cirrus short-wave cloud forcing.

4. Less polluted convective clouds in the southern margin of the ITCZ: this region will serve as a reference for reservoir 3.

5. Less polluted cloud-topped marine boundary layer and cloud-free air south of the ITCZ: this would be the reference for reservoirs 1 and 2.

The experiment will consist of an intensive field phase lasting about 1.5 months and an "enhanced" observational period of at least four months with satellites and available ships, buoys and drifter observations. The particular domain for the field phase has not been chosen, but the ship and flight tracks will most likely be confined to the north-south direction between 55šE to 65šE.

Field phase

The following platforms will be used during the field phase:

* Radiation, microphysics, chemistry, water vapor, precipitation and other meteorological data will be collected from 2 to 3 aircraft and at least one ship.

* Collocated and real time satellite meteorological data from polar-orbiting National Oceanic and Atmospheric Administration (NOAA) and Defense Meteorological Satellite Program (DMSP) satellites and geo-stationary INSAT satellite.

* Earth radiation budget data from the French Scanner for Earth Radiation Budget (SCARAB) instrument are important for this experiment.

* In addition, if the Tropical Rainfall Measuring Mission (TRMM) has been successfully launched by then, the rainfall and radiation budget data will significantly enhance the value of INDOEX. Furthermore, the aircraft and ship based Radar data can be used as ground truth for validating TRMM estimates of precipitation and surface radiation budget.

* Surface based calibrated measurements of aerosols, radiation, chemistry and soundings at Male and Mauritius (20.17°S, 57.33°E) will be a vital part of the field phase. Male will serve as the "control" for the polluted air, while Mauritius which is southwest of Maldives, will serve as the "control" for air entering the ITCZ from the southern Indian Ocean.

Enhanced observation phase

Historical data: Earth Radiation Budget Experiment (ERBE) scanner data for 1985 to 1990 and recent SCARAB data will be analyzed to understand the spatial and temporal evolution of ITCZ cloud systems and their radiative forcing; ship sondes for the period 1980 to 1990 will be analyzed to estimate the vertical distribution of water vapor across the ITCZ; ISCCP data for the 1985 to 1990 will be used to map out the cloud structure. Analysis of surface aerosol data (taken in India) will be undertaken. Surface observations of aerosols, including their composition, from India and the Far East are very critical to the planned experiment.

Analyzed and model fields: Analyzed dynamical fields from the ECMWF, the Laboratoire de Météorologie Dynamique (LMD) and T-106 Florida State models for a period of about 2 years (for December-April period) will be used to characterize the transport properties and the variation in the monsoonal inversion. In addition, 3-dimensional fields will be derived for the Indian Ocean region using satellite data analysis.

Extended experimental phase: i) We also envisage a strong need for a few buoys to monitor surface winds, humidity, SST, rainfall and radiation fluxes, in the domain of interest. Such observations are needed for periods of at least two years, one year before and one year after the experiment and also during the experiment. Easy to maintain and automated ground measurements (e.g., column aerosol optical depth, ozone, radiation fluxes) at Male and Mauritius will be undertaken for the 2 year period; and ii) A four month long (including the 6 to 8 week field phase) calibrated observation from the two island sites will be collected, which will include water vapor and ozone sondes, vertical distribution of aerosols and winds from a profiler. In addition, since very little is known about this region, pre-INDOEX cruises will be required to ensure the success of the experiment. The following activities are underway:

* With major support from C⁴, a recent exploratory experiment was conducted in the Indian Ocean from the NOAA's R/V Malcolm Baldrige. A team from the University of Maryland consisted of R. Dickerson, P. Kelley, K. Rhoads, F. Miskolczi, and P. Pinker, in collaboration with J. Prospero (University of Miami); T. Carsey, M. Farmer (NOAA/AOML); and S. Oltmans (NOAA/CMDL). The team measured trace gases, bulk aerosol, and surface meteorological variables; ozone, humidity and temperature aloft, aerosol optical depth. The results are currently being analyzed.

* The Max Planck Institute (MPI-Mainz) is making surface ozone measurements from a merchant ship over the domain of interest (Figure 8).

* A. P. Mitra (coordinator of global change programs in India), C⁴ and MPI are co-sponsoring measurements of water vapor, ozone, aerosols and radiation fluxes on board an Indian research vessel between 1996 and 1998.

* R. Davis of Scripps Institution of Oceanography (SIO), a principal investigator in the World Ocean Circulation Experiment (WOCE), has agreed to provide us with access to drifter data that will be collected beginning in the Fall of 1995 over the Bay of Bengal and the Indian Ocean. These data are critical for understanding the regional patterns of SST and evolution of the warm pool, which in turn are required to understand the evolution and migration of the ITCZ. If found necessary, such data will also be collected during the experimental phase.

Role of Models

Models will play a substantial role in the design of the experiment and in the post-field phase analysis. Atmospheric GCMs and three dimensional transport models will be employed to guide the experimental design and plan. Participation by four modeling groups at Florida State University (FSU), LMD, MPI and the National Center for Atmospheric Research (NCAR) will facilitate access to these models, all of which perform monsoon simulation as well as simulate the transport of trace species including sulfates. One example of this simulation is Figure 10, which shows parcel trajectories of an inert trace gas with sources from various cities in India. In addition, C⁴ (NCAR, MPI and SIO) has developed an equatorial chemistry model. This model, which is currently being validated with CEPEX data, will be used to simulate the chemistry of reactive species in the Indian Ocean. Another example of a pre-field phase model study is one by LMD, which is currently undertaking the analysis of the NE monsoon and its transition to SW monsoon in an ensemble of simulation, including one 10-year Atmospheric Models Intercomparision Project (AMIP) simulation, and an ensemble of 16 independent 4-year simulations of the 1986-1989 period (Figure 11).

1st startdate: SUNDAY 3 JANUARY 1993 0 GMT last startdate: SATURDAY 30 JANUARY 1993 0 GMT

Figure 10. Trajectory Calculation. The trajectory starting points are located in the middle of the boundary layer to stimulate pollution transports from 4 major source regions in India: Madras (blue), Bombay (pink), Calcutta (black) and Delhi (green). The trajectories, calculated 18 hours apart from January 1 to April 30, are grouped according to starting hour (GMT) per month. The trajectories are marked by their starting date and time (e.g., 93032012 is 20 March 1993 at 12 GMT). (Courtesy of the Royal Netherlands Meteorological Institute)

Figure 11. January-February average wind velocities at 950mb for 1987 (left) and 1988 (right), from an ensemble average of 16 independent four-year simulations of the 1986-1989 period with the LMD AGCM forced by observed SST's. (Courtesy of R. Sadourny and A. Harzallah)

Ongoing and Planned Aerosol Related Experiments

A number of national and international programs have been initiated to address the aerosol-climate, chemistry and climate change issue (Table 2). The design of the INDOEX program will take great care to avoid duplication. Furthermore, INDOEX measurements should complement the objectives of these programs and fill critical gaps.

Other Experiments in the Indian Ocean

The WOCE program will be conducting a field experiment in the Indian Ocean during 1995 with a thrust on ocean circulation (WOCE Planning Document). The data collected by WOCE and the Joint Global Ocean Flux Study (JGOFS) will be very valuable for planning INDOEX. In addition, the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME) has been planned to be in operation during the proposed INDOEX. This large program will focus on the Asian monsoons and the surface hydrological process (GAME Planning Document, 1993).

Proposal, Funding and International Participation

INDOEX is an international experiment. Funding for some of the pre-INDOEX studies are made available from existing resources within C⁴ and the other participating institutions. For the rest, including the field phase, we will seek participation and funding support from the funding agencies in France, Germany, India, the Netherlands and the U.S.

C⁴ will assemble a small group of U.S. experimentalists, modelers and theoreticians with interests and expertise in the proposed effort to articulate a full-fledged proposal to be submitted to the U.S. funding agencies. In particular, we will seek participation from aerosol experts in the U.S. The NOAA Aeronomy Laboratory (S. Liu and A. Tuck) has expressed interest in participating in INDOEX. The U.S. proposal will be coordinated with planned activities by the participating nations.

Interested principal investigators from international institutions participated in a workshop held at NCAR on February 16, 1995 and another one at MPI-Chemistry in Mainz, Germany on June 26-27, 1995. Their proposed INDOEX-related activities are listed in Table 3 on the inside back cover. Under the direction of P. J. Crutzen we will approach the German, Dutch, and European Union funding agencies for some of the airborne chemistry measurements and for data analysis by German/Dutch scientists. D. Kley will work with Professor H. Graßl to secure support for a German ship. R. Sadourny will seek French funding for balloons, satellite data analysis and GCM model studies. J. Lelieveld will submit a Dutch proposal for participation of an aircraft and for chemistry modeling. A. P. Mitra will seek Indian government support for the participation of research vessels from India's Institution of Oceanography, aerosol measurements, access to INSAT satellite data, and analysis of available surface observations.

Table 2. List of Current Aerosol Related Projects Projects Duration Field-Phase Location ACE-1 15 Nov - 14 Dec 1995 SW Pacific ACE-2 June - July 1997 N. Atlantic AEROCE 1 Oct 1994 - 30 Sept 1998 N. Atlantic IGAC/IGAP Next two-three years (see ACE), Arctic, Siberia, Amazon, existing data NARE Summer 1993 Winters 1993-94 Winter-Spring 1995-97 N. Atlantic ACE-1: Southern Hemisphere Marine Aerosol Characterization Experiment ACE-2: Northern Hemisphere Marine Aerosol Characterization Experiment. Both ACE-1 and -2 are joint efforts of the International Global Atmospheric Chemistry Project's (IGAC) Multiphase Atmospheric Chemistry (MAC) Activity and Marine Aerosol and Gas Exchange (MAGE) Activity. AEROCE: Atmosphere/Ocean Chemistry Experiment IGAP: International Global Aerosol Program (now merged with IGAC) NARE: North Atlantic Regional Experiment. Initial focus of NARE is to determine the impact of emissions of pollutants which lead to the production of tropospheric ozone.