Regional Aerosol-Chemistry-Climate Observatories for the Indo-Asia-Pacific Region (Project Atmospheric Brown Cloud) and the Maldives Autonomous UAV Campaign (MAC)
Link to NOAA Strategic Plan: NOAA’s Mission Goal 2: Understand Climate Variability and Change to Enhance Society’s Ability to Plan and Respond
RESEARCH OBJECTIVES AND SPECIFIC PLANS TO ACHIEVE THEM
About 60 percent of the world’s population of 6 billion live in Asia. Environmental consequences of Asia’s rapid economic development can be far reaching, especially with respect to air pollution at local and regional levels. A recent international study, the Indian Ocean Experiment (INDOEX), documented the vast extent of the so-called Asian haze, a 3 km thick brownish layer of pollutants hovering over most of the tropical Indian Ocean, South, Southeast and East Asia. The haze particles consist of sulfates, nitrates, organics, black carbon and fly ash amongst several other pollutants, which can be transported far beyond their source region, particularly during the dry season. Potential direct and indirect consequences of the haze involve regional and global climate change, impacts on ecosystem, the water cycle, agriculture and human health. Significant reduction in the solar radiation reaching the surface; a 50-100% increase in solar heating of the lower atmosphere; rainfall suppression; agricultural productivity decline; and adverse human health effects. Preliminary results also indicate that the build up of the haze, a mash of ash, acids, aerosols and other particles, is disrupting weather systems including rainfall and wind patterns and triggering droughts in Western parts of the Asian Continent. The regional and global impacts of the haze are set to intensify over the next 30 years as the population of the Asian region rises to an estimated five billion people.
Since the regional and temporal scales of the pollution layer are not well known, high quality data on the haze and precursor pollutants are urgently needed to assess the long-term trends. There is also a need to find the answers to the following basic questions: What are the sources of the soot and the other major haze components? How are the aerosol particles transported, transformed, and ultimately removed from the atmosphere? How does the solar heating in the haze affect the monsoon rainfall? How does the reduction of solar energy to the surface affect the water budget and soil moisture? Does the haze amplify or ameliorate the warming due to greenhouse gases? Before the policy issues can be rationally addressed, these questions need to be answered.
A project called Atmospheric Brown Cloud has been initiated jointly by UNEP and the Center for Clouds, Chemistry and Climate (C4) at the Scripps Institution of Oceanography (C4/SIO). Under Project ABC scientists plan to establish a network of ground-based monitoring stations throughout Asia to study the composition and seasonal pattern of the haze. UNEP has pledged to facilitate and assist with science, research and capacity building program and bring the results to attention of Governments. The U.S. observation program in ABC has been funded by NOAA since 2002. Starting in 2004, SIDA, the Swedish International Development Cooperation Agency is providing funding support to UNEP for the implementation of ABC Capacity Building and Impacts Assessment. The website http://www-abc-asia.ucsd.edu offers a complete and current description of Project ABC and related programs.
RESEARCH ACCOMPLISHMENTS
The past year was devoted mainly to data analyses and publication of the Maldives Autonomous-UAV Campaign (MAC). In addition, in the Spring 2007 the ABC Team in collaboration with ABC scientists in Asia participated in the ABC-East Asia Regional Experiment (EAREX) 2007, forming the ground observations network for the Pacific Dust Experiment (PACDEX).
During March 2006, in the Maldives Autonomous-UAV Campaign (MAC), the polluted atmosphere over the N. Indian Ocean was probed with lightweight Unmanned Aerial Vehicles (or UAVs) fully equipped with instruments. This UAV campaign has laid a solid foundation for the use of UAVs to study how mankind is polluting the atmosphere and the consequential impacts on climate, including global warming. Since the UAVs were flown in a stacked formation (above clouds at 10,000 feet, at cloud level thus penetrating clouds about 3,000 feet, and below cloud level at 1,500 feet) in 18 missions, unique measurements were feasible.
Measurements of vertical profiles of total particle concentration, particle size distributions, absorption, and black carbon concentrations indicate that surface measurements are not always reliable for understanding the aerosol properties within the entire vertical column, especially if the column is influenced by long-range transport.
Measurements of albedo, atmospheric absorption, and atmospheric heating rates in the visible and broadband regions using vertically stacked multiple UAVs. The most significant finding of this study, is that when absorbing aerosols are measured and accounted for in models, and when heating rates are measured directly with stacked aircraft, the model clear sky heating rates agree with observed heating rates and there is no need to invoke significant anomalous or excess absorption in clear skies.
Since the 3 UAVs were flown within a horizontal separation of tens of meters and a temporal separation less than 10 seconds, the solar heating rates could be measured directly. Long-range transport led to a 3-km thick layer of atmospheric brown clouds (ABCs) and the ABCs enhanced lower atmospheric solar heating by about 50%.
The indirect effect could be measured for the first time. The enhancement in cloud albedo is directly measured on a cloud-by-cloud basis and linked to increasing aerosol concentrations using multiple autonomous unmanned aerial vehicles to simultaneously observe the cloud microphysics, the vertical aerosol distribution, and the associated solar radiative fluxes.
At the time of this report, a study is near publication stage on 3-D cloud radiation interactions comparing broadband radiation flux data obtained with stacked UAV observations with 3D-radiative transfer Monte Carlo models for the MAC cloud field of 24 March 2006.
During ABC-EAREX2007, surface observations from a number of sites in China, Japan and Korea were carried out for the study of radiation budget and aerosol properties over East Asia, which were the indispensable part of the 2007 Pacific Dust Experiment (PACDEX) involving the new Gulfstream V research aircraft from NCAR. The goal of PACDEX, a pioneering airborne study using Lagrangian sampling, was to observe the evolution of Eurasian-Pacific-North American dust-soot-cloud system.
Fig. 1
Vertical distribution of UAV observations. The MAC period is divided into two periods: Period-1 for March 4 to 16 when aerosol was mainly below 1 km; and Period-2 for March 19 to 29, when aerosol was elevated. a) Aerosol absorption coefficient (Mm-1) for period-1 (black) and period-2 (red). b) Diurnally averaged solar heating rate (H) for period-1. The instantaneous fluxes were normalized to diurnal average solar fluxes using MACR simulations to obtain diurnal mean H. Vertical bar shows the layer depth; horizontal bar shows the variations between flight legs, with each flight lasting about 25 minutes; solid circles are observed values and diamonds are simulated values by MACR. c) Same as b but for period 2. d) Difference in the vertically (0.5 km 3 km) averaged H between period 2 and period 1. The green line is the MACR profile for ΔH. The spatially average over Indian Ocean and S Asia of the specified CCM3 ABC heating is also shown. The uncertainty in H is 0.3 K/day for period-1 and 0.2 K/day for period-2. All uncertainty estimates are 2- σ values
Fig. 2
During MAC, it was demonstrated that aerosol-cloud-albedo interactions could be directly observed provided a minimum of 3 AUAVs are deployed simultaneously below, inside and above the clouds. a) Relationship between flight rms-averaged CCN concentrations (at 0.1% Sc; NCCN_0.1) and maximum in-cloud droplet concentrations (nD,max) for all cloud flights. Diamonds indicate simulated NCCN_0.1 in period II based on aerosol size distributions and assumed chemistry. The dashed line represents the 1:1 correlation. b) Distance along flight track showing the simultaneous measurements of cloud microphysical and radiometric properties from three AUAVs at different altitudes. The in-cloud measurements (nD, Reff, and droplet distribution) are shown in the bottom panel. The observed broadband albedo (0.3 to 2.8 mm) is shown by the red line in the top two panels. Model response in a) are calculated based on characteristic length, w*, and cloud albedo, ac = 0.826—black and green dashed lines from 1200 masl cloud top and 600 and 400 m cloud width, respectively; blue dashed line from 1300 masl cloud top and 400 m cloud width. The shaded blue region illustrates Dac ± 0.1. Thin horizontal dashed lines show the minimum albedo during the leg. Altitudes for the AUAVs are shown in each panel
