Publication Abstracts
Stramler 2006
, 2006: The Influence of Synoptic Atmospheric Motions on the Arctic Energy Budget. Ph.D. thesis. Columbia University.
While rendered plausible by observational evidence, the amplified Arctic response to a doubling of atmospheric carbon dioxide concentrations that is seen in global climate model (GCM) simulations is not yet defensible. As such, it is necessary to ascertain whether the Arctic sensitivity is an integral characteristic of the Arctic climate, or if it arises from errors in model formulation.
Thus, how the character of Arctic surface and atmosphere change as they respond to synoptic influxes of moisture and temperature is examined here, with the intent to document those hourly to diurnal energy exchange mechanisms that are essential for climate models to store energy in the appropriate climate constituents. This in hopes of enabling them to better represent locally occurring, short-term processes and ultimately assist in their representation of the longer time scale Arctic climate feedbacks.
Local processes at both an ice-covered Arctic Ocean site, SHEBA (Surface Heat Budget of the Arctic Ocean), and a tundra-covered coastal continental Arctic site, Point Barrow, are examined, in hopes of general applicability to Arctic regions having these surface types. The Point Barrow site affords an examination of interannual variability as the ARM (Atmospheric Radiation Measurement Program) NSA (North Slope of Alaska) Point Barrow installation has been operational since 1998.
How the variability of atmospheric temperature, water vapor, and clouds modifies the quantity of radiation received by the Arctic surfaces at these two sites has also been briefly examined, using the GISS (Goddard Institute for Space Studies) SCM (Single Column Model) radiation code. During the winter season, there are two distinct quasi-equilibrium states preferred by the SHEBA surface, sub-surface, and atmosphere: a clear state, with remarkably consistent properties throughout the vertical column, and a warmer and moister cloudy state, also having remarkably consistent properties. The cloudy state may be triggered during either the high or low phase of a baroclinic wave, whereas the clear state occurs only under anti-cyclonic conditions.
The same mechanisms driving the SHEBA winter surface, sub-surface, and atmosphere response to the influx of atmospheric temperature and moisture are utilized during the bulk of the spring season at SHEBA, when the constituent media increase temperature as consequence of synoptic influxes, but not pertinent for the summer season, when all processes over perennial sea ice are limited by the melting temperature and heat capacity of the surface.
Temperature and humidity characteristics of the SHEBA winter atmosphere appear to be a cold extreme for the NSA winter atmosphere, but one that is visited with less than 50% frequency over the 5-year period examined here. The surface flux and temperature characteristics at SHEBA are unique to SHEBA however, as the NSA surface temperatures tend to be higher, and the surface fluxes less distinct between cloudy and clear sky values. This difference between the radiation climatology of the two sites is explained by the directions and proximity from which synoptic scale weather systems approach the two Arctic sites.
The GISS SCM radiation code is found to require scaling of absorbing gases H2O and O3 by 0.5 in order to reproduce observed clear sky fluxes over the Arctic. Even given this adjustment, the SCM is able to reproduce from 60-80% of the observed clear sky winter LWD distributions at SHEBA and NSA, with approximately 5 W/m2 error. At both sites and on seasonal and interannual time scales, it is the variability of temperature that essentially determines clear sky LWD variations, whereas the variability of water vapor plays a much lesser role. The bimodal nature of the LWD distribution occurs because of the relative absence of clouds having optical depths between 0.75-4 units, and the opaque clouds which constitute the NetLW — 0 W/m2 mode must have optical depth near 4 units and be near the peak of the temperature inversion in order for the SCM to obtain the observed LWD.
In order for GCMs to accurately depict Arctic climate, representations of the following Arctic processes must be adequate on time scales of an hour (at which time scale the GCM radiation must be updated): the atmospheric inversion structure for the clear and cloudy sky NetLW modes, the vertical distribution of optical depth for the cloudy sky mode, gravitational settling of ice crystals, sub-surface temperature variations under all sky conditions, and the sub-surface energy storage during opaquely cloudy episodes. If capable of capturing these mechanisms of energy transfer, which are the mechanisms here demonstrated to be in use as the Arctic climate system is currently configured, and if capable of generating statistically plausible frequencies of baroclinic wave passage, GCMs should be able to reliably constrain the bounds of the Arctic temperature amplification.
Export citation: [ BibTeX ] [ RIS ]
BibTeX Citation
@phdthesis{st01510r,
author={Stramler, K. L.},
title={The Influence of Synoptic Atmospheric Motions on the Arctic Energy Budget},
year={2006},
school={Columbia University},
address={New York, N.Y.},
}
[ Close ]
RIS Citation
TY - THES ID - st01510r AU - Stramler, K. L. PY - 2006 BT - The Influence of Synoptic Atmospheric Motions on the Arctic Energy Budget PB - Columbia University CY - New York, N.Y. ER -
[ Close ]
