Short Title: HIAA Proposal URL: http://classic.ipy.org/development/eoi/proposal-details.php?id=140 We propose to establish a program to investigate the interactions among aerosols, clouds and precipitation in the Arctic, and the impact of variations and changes in aerosol characteristics on precipitation, snow cover, river flow, permafrost and surface temperature. Observations of increasing precipitation, rising river flow, declining snow cover, and thawing permafrost indicate substantial changes to the Arctic hydrological cycle. Variations and changes in the Arctic hydrological cycle are likely to arise from a complex interplay between natural internal modes of climate variability and anthropogenic activity. Variations in atmospheric aerosol characteristics have the potential to modulate the Arctic hydrological cycle both directly through its impact on precipitation and also indirectly through its impact on temperature. Atmospheric aerosols influence the nucleation of cloud particles, which influences directly the cloud cover and precipitation processes, and hence forces variations in the river runoff, snow cover, permafrost, glacial accumulation, and surface temperature. Biomass burning in the northern forests, pollution aerosol, biogenic aerosol, and desert dust have been proposed as significant sources of Arctic aerosol. During the IPY, we will examine seasonal and regional variations, focusing on the North American Arctic and the Eurasian Arctic land regions. We will establish a multi-disciplinary observing network of atmospheric and surface hydrological observations, integrating existing observations (surface and satellite) and supplementing them with UAV measurements and enhanced surface observations during a special field campaign. Diagnostic and modeling studies will be conducted to document and understand the role of variations of aerosols in influencing variations of the Arctic hydrological cycle, towards predicting these variations and using these predictions in regional decision making. We will attempt to clarify the interactions between warming and variations in aerosol characteristics on the changing Arctic hydrological cycle. The field measurements undertaken during the IPY will be placed in a broader context through the synthesis of recent field observations, regional model development efforts, historical data sets, and global model simulations to assess the current status and research required for substantially improved predictions of Arctic precipitation and an assessment of the role of aerosols in forcing variations in the arctic hydrological cycle. To address this goal, we will conduct the following: i) Statistical analysis of local precipitation variability in the selected basins for the past 50 years, and interpretation of this variability in the context of internal modes of climate variability, local topography, local measurements of aerosol optical depth, and proximity to local sources of air pollution. ii) Application of a mesoscale model with sophisticated cloud microphysical processes to investigate the sensitivity of precipitation amount and phase to aerosol physical and chemical characteristics, to simulate the impact of biomass burning, pollution aerosol, volcanic aerosol, and desert dust. iv) Application of winter/spring mesoscale simulations using varying aerosol characteristics to force the Catchment-based land Surface Model (CLSM) in the selected basins to assess the impact of aerosol variations on runoff, timing of snow melt, evapotranspiration, soil moisture, and permafrost. v) Assessment of the potential for seasonal and subseasonal predictability of snow melt and permafrost thaw and the disappearance of the snow roads.
HIAA
G - I