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Introduction

1990's: Decade of New Discoveries

The 1980's brought clear evidence that the earth system is susceptible to global-scale changes at rates unimagined ten years ago. The 1990's represent a critical period during which fundamental advances in our understanding of feedback processes which control the rates of global change must be quantified for informed policy decisions.
From a mechanistic point of view, much of the earth's atmosphere remains unexplored: Cloud/radiative feedback, sources and sinks of carbon, tropospheric oxidation, microphysics of tropical convection, free radical catalysis, stratosphere/troposphere exchange, to select a few. Implicit in what follows is the distinction between mechanistic or process oriented studies and observations of climatology. While both are essential for scientific progress, a balance must be struck in our national strategy. Identifying the scale and blend of the research effot -- the intellectual disciplines, the human resources, the research facilities, the international agreements, etc. -- is an essential problem facing us all.

1990's: Decade for a Balanced Scientific Program in Global Change
Why are unmanned aircraft an ideal companion to satellite programs in the nation's Global Change research program? In part, the answer hinges on the following points:

1. Unmanned aircraft provide immediate data addressing key questions on climate change, polar ozone depletion, tropospheric oxidation rates, impact of high-speed civil transports, and severe storms.

2. Unmanned aircraft provide complementary data to the current large satellite platforms proposed for the decade's end. High spatial and temporal resolution information on the global scale can be obtained from the ground to altitudes of 30-35 km.
* Radiation field measurements: Flux (and radiance) divergence and directionality with cloud properties and constituent concentrations from the surface to 30 km, which are essential for global warming and related climate change studies
* Global carbon cycle: Sources/sinks of CO2 and CH4 over open ocean, ice pack, tundra, jungles, marshes, etc., which are required to identify key players in the carbon cycle
* Water vapor: High accuracy/precision measurements of H2O concentrations between 5 and 25 km are needed to estimate the sign and magnitude of the water vapor-greenhouse effect feedback
* Ozone and water vapor: High accuracy/precision observations in the upper troposphere and in the stratosphere
* Simultaneous high accuracy observations with high spatial resolution of the catalytically active species (in ozone destruction processes): OH, HO2, Cl, ClO, BrO, NO, NO2, O(3P)
* Diagnostics for atmospheric dynamics: Atmospheric tracers (N2O, CFC 11/12, CH4) required to identify air parcel trajectories
* Atmospheric structure: Winds, temperatures, lapse rates, potential vorticity, potential temperature, gravity waves
* Reactive reservoir species H2O, HONO2, HCl, ClONO2, ClOOCl, Cl2
Particle size (0.01 u to 20 u), concentration, shape, composition
* Cloud microphysical properties; cirrus, stratus, etc.

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