291 research outputs found
A First Look at NGRIP Surface Climatology (1997-2001) Using Automatic Weather Station Data
Greenland ice sheet automatic weather station (AWS) data provide high temporal resolution climate information for NGRIP (75.09980° N, 42.3326° W. 2918 m), where a tremendously long ice core climate record is becoming available. In this paper, an overview is made or the surface climatology or NGRIP to support work on ice core interpretation using GRIP meteorological observations and snow pits. Valuable perspective is given by comparison of NGRIP climate with other deep ice core sites (Summit and Camp Century), where AWS data are also available.NASANational Science Foundatio
Improving Surface Mass Balance Over Ice Sheets and Snow Depth on Sea Ice
Surface mass balance (SMB) over ice sheets and snow on sea ice (SOSI) are important components of the cryosphere. Large knowledge gaps remain in scientists' abilities to monitor SMB and SOSI, including insufficient measurements and difficulties with satellite retrievals. On ice sheets, snow accumulation is the sole mass gain to SMB, and meltwater runoff can be the dominant single loss factor in extremely warm years such as 2012. SOSI affects the growth and melt cycle of the Earth's polar sea ice cover. The summer of 2012 saw the largest satellite-recorded melt area over the Greenland ice sheet and the smallest satellite-recorded Arctic sea ice extent, making this meeting both timely and relevant
Regional Greenland Accumulation Variability from Operation IceBridge Airborne Accumulation Radar
The mass balance of the Greenland Ice Sheet (GrIS) in a warming climate is of critical interest to scientists and the general public in the context of future sea-level rise. An improved understanding of temporal and spatial variability of snow accumulation will reduce uncertainties in GrIS mass balance models and improve projections of Greenland\u27s contribution to sea-level rise, currently estimated at 0.089 ± 0.03 m by 2100. Here we analyze 25 NASA Operation IceBridge accumulation radar flights totaling \u3e 17 700 km from 2013 to 2014 to determine snow accumulation in the GrIS dry snow and percolation zones over the past 100–300 years. IceBridge accumulation rates are calculated and used to validate accumulation rates from three regional climate models. Averaged over all 25 flights, the RMS difference between the models and IceBridge accumulation is between 0.023 ± 0.019 and 0.043 ± 0.029 m w.e. a−1, although each model shows significantly larger differences from IceBridge accumulation on a regional basis. In the southeast region, for example, the Modèle Atmosphérique Régional (MARv3.5.2) overestimates by an average of 20.89 ± 6.75 % across the drainage basin. Our results indicate that these regional differences between model and IceBridge accumulation are large enough to significantly alter GrIS surface mass balance estimates. Empirical orthogonal function analysis suggests that the first two principal components account for 33 and 19 % of the variance, and correlate with the Atlantic Multidecadal Oscillation (AMO) and wintertime North Atlantic Oscillation (NAO), respectively. Regions that disagree strongest with climate models are those in which we have the fewest IceBridge data points, requiring additional in situ measurements to verify model uncertainties
Causes of Greenland temperature variability over the past 4000 years: Implications for North Hemispheric temperature change
第3回極域科学シンポジウム/第35回極域気水圏シンポジウム 11月29日(木) 国立国語研究所 2階多目的
Mapping daily snow/ice shortwave broadband albedo from Moderate Resolution Imaging Spectroradiometer (MODIS): The improved direct retrieval algorithm and validation with Greenland in situ measurement
Snow/ice albedo is a critical variable in surface energy balance calculations. The
Moderate Resolution Imaging Spectroradiometer (MODIS) data have been used routinely
to provide global land surface albedo. The MODIS algorithm includes atmospheric
correction, surface reflectance angular modeling, and narrowband to broadband albedo
conversion. In an earlier study, a "direct retrieval" methodology was proposed to calculate
instantaneous albedo over snow and ice-covered surfaces directly from top-of-atmosphere
(TOA) MODIS reflectance data. The method consists of extensive radiative transfer
simulations for a variety of atmospheric and surface snow conditions and links the TOA
reflectance with surface broadband albedo through regression analysis. Therefore the
direct retrieval algorithm implicitly incorporates in a single step all three procedures used
in the standard MODIS surface albedo algorithm. This study presents improvements to the
retrieval algorithm including validation with in situ measurements distributed over the
Greenland ice sheet. Comparison with surface observations demonstrates that the direct
retrieval algorithm can produce very accurate daily snow/ice albedo with mean bias of less
than 0.02 and residual standard error of 0.04
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