scholarly journals Microwave Emission From Snow and Glacier Ice

1976 ◽  
Vol 16 (74) ◽  
pp. 23-39 ◽  
Author(s):  
T.C. Chang ◽  
P. Gloersen ◽  
T. Schmugge ◽  
T.T. Wilheit ◽  
H.J. Zwally
Keyword(s):  
Accumulation Rate ◽  
Mie Scattering ◽  
Microwave Emission ◽  
Mean Annual Temperature ◽  
Particle Sizes ◽  
Grain Sizes ◽  
Glacier Ice ◽  
The Mean ◽  
The Individual ◽  
Two Parameters

AbstractThe microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.

scholarly journals Microwave Emission From Snow and Glacier Ice

1976 ◽  
Vol 16 (74) ◽  
pp. 23-39 ◽  
Author(s):  
T.C. Chang ◽  
P. Gloersen ◽  
T. Schmugge ◽  
T.T. Wilheit ◽  
H.J. Zwally
Keyword(s):  
Accumulation Rate ◽  
Mie Scattering ◽  
Microwave Emission ◽  
Mean Annual Temperature ◽  
Particle Sizes ◽  
Grain Sizes ◽  
Glacier Ice ◽  
The Mean ◽  
The Individual ◽  
Two Parameters

AbstractThe microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in a manner similar to that used in calculating microwave and optical properties of clouds. The extinction coefficient is computed as a function of both microwave wavelength and ice-particle radius. Volume scattering by the individual ice particles in the snow field significantly decreases the computed emission for particle radii greater than a few hundredths of the microwave wavelength. Since the mean annual temperature and the accumulation rate of dry polar firn mainly determine the grain sizes upon which the microwave emission depends, these two parameters account for the main features of the 1.55 cm emission observed from Greenland and Antarctica with the Nimbus-5 scanning radiometer. For snow particle sizes normally encountered, most of the calculated radiation emanates from a layer on the order of 10 m in thickness at a wavelength of 2.8 cm, and less at shorter wavelengths. A marked increase in emission from wet versus dry snow is predicted, a result which is consistent with observations. The model results indicate that the characteristic grain sizes in the radiating layers, dry-firn accumulation rales, areas of summer melting, and physical temperatures, can be determined from multispectral microwave observations.

scholarly journals Characteristics of the Initial Densification of Snow/Firn in Wilkes Land, East Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 209-209
Author(s):  
Qin Dahe ◽  
N. W. Young
Keyword(s):  
Accumulation Rate ◽  
Viscosity Coefficient ◽  
East Antarctica ◽  
Shallow Depth ◽  
Mean Annual Temperature ◽  
List Type ◽  
Densification Rate ◽  
The Core ◽  
Wilkes Land ◽  
The Mean

Fourteen shallow snow/firn cores were drilled with the Polar Ice Coring Office light-weight hand-coring auger in Wilkes Land, along a line approximately long. 111°E between lat. 66° and 74°S. Five of these cores, all between 20 and 30 m deep, are studied in detail in this paper: LJ, BJ, GC30, GC40 and GC46. The physical geographical conditions differ at these five stations, but the general trend is for mean annual accumulation rate and mean annual temperature to decrease farther south, with increasing elevation. At the southernmost station, GC46, the mean annual temperature is –52.5°C, and accumulation rate is 52 kg m−2 a−1.The density measurements of the snow/firn were made in a cold-room at temperatures from –14− to –18−C, by taking consecutive samples from the core and measuring the mass of each sample of known volume. The characteristics of the initial densification (to a density of 550 kg m−3) – variation in snow/firn density with depth, the densification rate of snow/firn, and the compactive viscosity coefficient of snow/firn – are studied, and the factors affecting this initial densification process are discussed.The following observations were made and conclusions reached:1.Plots of all the measurements, from each core, of density against depth showed three different patterns. The first type, typical of the coastal areas, shows a very great variability of density at shallow depth, reducing with an increase in depth. The second, typical of the high inland stations, shows a smaller scatter of densities at shallow depth, again reducing with an increase in depth. The third type is a pattern intermediate between these two. So, the range of density fluctuation with a depth range in any core is greater at the top of the core than at the bottom, and at the same depth in different cores the variation in density is greater where the mean annual temperature is higher.2.The snow/firn density increases with an increase in depth at all stations, and the densification rate is higher at stations with higher mean annual temperature.3.The mean density of snow/firn in the top 1 m decreases farther inland, and this decrease appears to be closely related to the decrease in temperature.4.The mean densification rate is compared with the mean annual temperature and the mean annual accumulation rate over the past 40 years in the most southerly cores. The mean annual temperature is found to be the more important factor affecting the densification rate in the surface snow/firn on the cold ice sheet.5.At each station, for ρ = 550 kg m−3, a linear relationship is found between log compactive-viscosity coefficient of snow/firn and mean annual temperature for a constant density. If only stations with a mean annual temperature below –25°C (i.e. no melt features are present in the stratigraphy) are considered, then these results from Wilkes Land are very similar to the results obtained by Nishimura and others (1983) from Mizuho Plateau, East Antarctica.

scholarly journals Characteristics of the Initial Densification of Snow/Firn in Wilkes Land, East Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 209 ◽  
Author(s):  
Qin Dahe ◽  
N. W. Young
Keyword(s):  
Accumulation Rate ◽  
Viscosity Coefficient ◽  
East Antarctica ◽  
Shallow Depth ◽  
Mean Annual Temperature ◽  
List Type ◽  
Densification Rate ◽  
The Core ◽  
Wilkes Land ◽  
The Mean

Fourteen shallow snow/firn cores were drilled with the Polar Ice Coring Office light-weight hand-coring auger in Wilkes Land, along a line approximately long. 111°E between lat. 66° and 74°S. Five of these cores, all between 20 and 30 m deep, are studied in detail in this paper: LJ, BJ, GC30, GC40 and GC46. The physical geographical conditions differ at these five stations, but the general trend is for mean annual accumulation rate and mean annual temperature to decrease farther south, with increasing elevation. At the southernmost station, GC46, the mean annual temperature is –52.5°C, and accumulation rate is 52 kg m−2 a−1. The density measurements of the snow/firn were made in a cold-room at temperatures from –14− to –18−C, by taking consecutive samples from the core and measuring the mass of each sample of known volume. The characteristics of the initial densification (to a density of 550 kg m−3) – variation in snow/firn density with depth, the densification rate of snow/firn, and the compactive viscosity coefficient of snow/firn – are studied, and the factors affecting this initial densification process are discussed. The following observations were made and conclusions reached: 1. Plots of all the measurements, from each core, of density against depth showed three different patterns. The first type, typical of the coastal areas, shows a very great variability of density at shallow depth, reducing with an increase in depth. The second, typical of the high inland stations, shows a smaller scatter of densities at shallow depth, again reducing with an increase in depth. The third type is a pattern intermediate between these two. So, the range of density fluctuation with a depth range in any core is greater at the top of the core than at the bottom, and at the same depth in different cores the variation in density is greater where the mean annual temperature is higher. 2. The snow/firn density increases with an increase in depth at all stations, and the densification rate is higher at stations with higher mean annual temperature. 3. The mean density of snow/firn in the top 1 m decreases farther inland, and this decrease appears to be closely related to the decrease in temperature. 4. The mean densification rate is compared with the mean annual temperature and the mean annual accumulation rate over the past 40 years in the most southerly cores. The mean annual temperature is found to be the more important factor affecting the densification rate in the surface snow/firn on the cold ice sheet. 5. At each station, for ρ = 550 kg m−3, a linear relationship is found between log compactive-viscosity coefficient of snow/firn and mean annual temperature for a constant density. If only stations with a mean annual temperature below –25°C (i.e. no melt features are present in the stratigraphy) are considered, then these results from Wilkes Land are very similar to the results obtained by Nishimura and others (1983) from Mizuho Plateau, East Antarctica.

scholarly journals Developing a bubble number-density paleoclimatic indicator for glacier ice

2006 ◽  
Vol 52 (178) ◽  
pp. 358-364 ◽  
Author(s):  
M.K. Spencer ◽  
R.B. Alley ◽  
J.J. Fitzpatrick
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Published Data ◽  
Mean Annual Temperature ◽  
Number Density ◽  
Grain Number ◽  
Glacier Ice ◽  
A New Technique ◽  
Bubble Number ◽  
Bubble Number Density

AbstractPast accumulation rate can be estimated from the measured number-density of bubbles in an ice core and the reconstructed paleotemperature, using a new technique. Density increase and grain growth in polar firn are both controlled by temperature and accumulation rate, and the integrated effects are recorded in the number-density of bubbles as the firn changes to ice. An empirical model of these processes, optimized to fit published data on recently formed bubbles, reconstructs accumulation rates using recent temperatures with an uncertainty of 41% (P < 0.05). For modern sites considered here, no statistically significant trend exists between mean annual temperature and the ratio of bubble number-density to grain number-density at the time of pore close-off; optimum modeled accumulation-rate estimates require an eventual ~2.02 ± 0.08 (P < 0.05) bubbles per close-off grain. Bubble number-density in the GRIP (Greenland) ice core is qualitatively consistent with independent estimates for a combined temperature decrease and accumulation-rate increase there during the last 5 kyr.

scholarly journals Glaciological Reconnaissance of an Ice Core Drilling Site, Penny Ice Cap, Baffin Island

1984 ◽  
Vol 30 (104) ◽  
pp. 3-15 ◽  
Author(s):  
G. Holdsworth
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Surface Air Temperature ◽  
Tritium Concentration ◽  
Mean Annual Temperature ◽  
Climatic Data ◽  
Baffin Island ◽  
The Core ◽  
Ice Cap ◽  
The Mean

AbstractA site situated close to the main divide of the Penny Ice Cap, Baffin Island was occupied in 1979 for the purpose of determining the suitability of this ice cap for providing proxy climatic data and other environmental time series for a span of 104a. A 20 m core was extracted and analysed for stable oxygen isotopes, tritium concentration, pH, electrolytic conductivity, major ion concentrations, and particulate concentration. An adjacent dedicated shallow core was analysed for pollen content to determine if a significant seasonal variation in the pollen rain existed. From these measurements, and from the observations made on the stratigraphic character of the core, the mean net accumulation rate over the approximately 30 year period covered by the core is found to be about 0.43 m water equivalent per year. This is in agreement with a single value determined 26 years earlier at a nearby site (Ward and Baird, 1954). The mean annual temperature in the bore hole was found to be close to −14.4° C, possibly some 2–5 deg warmer than the expected mean annual surface air temperature at the site. This difference is due to the expulsion of latent heat upon freezing of melt water at depth in the snow-pack which gives rise to the many ice layers observed in the core. The percentage thickness of ice layers per year may be correlated with summer temperatures.Total ice depths were measured using a 620 MHz radar echo-sounder. In the vicinity of the divide, over an area of 1 km2, the ice depths vary from about 460 to 515 m. These values compare favourably with values determined from an airborne radar depth-sounding flight carried out over the ice cap by a joint U.S.–Danish mission operating out of Søndre Strømfjord, Greenland. The data suggest that the ice-cap divide would be a worthwhile location to deep core drill with an expected useful coverage of at least the Holocene period.

scholarly journals Glaciological studies on the King George Island ice cap, South Shetland Islands, Antarctica

1998 ◽  
Vol 27 ◽  
pp. 105-109 ◽  
Author(s):  
Wen Jiahong ◽  
Kang Jiancheng ◽  
Han Jiankang ◽  
Xie Zichu ◽  
Liu Leibao ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Stable State ◽  
Equilibrium Line ◽  
South Shetland Islands ◽  
Mean Annual Temperature ◽  
King George Island ◽  
Equilibrium Line Altitude ◽  
Shetland Islands ◽  
Ice Cap ◽  
The Mean

The King George Island ice cap, South Shetland Islands, Antarctica, was studied between 1985 and 1992. At the steady-state equilibrium-line altitude of the ice cap, the mean annual temperature is -3.6°C, the mean summer (December-February) temperature is 0°C and annual precipitation is 800 mm w.e. Precipitation increases rapidly with elevation, and annual accumulation rate at the Main Dome summit reaches 2480 mm a−1. Between 1985 and 1991 the equilibrium-line elevation averaged 140-150 m a.s.l. The ice cap has been in an overall stable state for the past 20 years, going from a weak negative to a small positive mass imbalance as increased precipitation outweighs the effects of rising temperatures. Temperatures at the bottom of the active layer over most of the accumulation area are close to 0°C, with colder temperatures down to -1.9°C in the ablation zone. Soluble impurities in the ice cap are mainly from marine sources, while undissolved mineral material amounts to only 15-54% of the total microparticle content.

scholarly journals Glacio-meteorological and isotopic studies along the EGIG line, central Greenland

1995 ◽  
Vol 41 (139) ◽  
pp. 515-527 ◽  
Author(s):  
H. Fischer ◽  
D. Wagenbach ◽  
M. Laternser ◽  
W. Haeberli
Keyword(s):  
Geographical Distribution ◽  
Accumulation Rate ◽  
Western Slope ◽  
Mean Annual Temperature ◽  
Depth Range ◽  
The West ◽  
Altitude Gradient ◽  
Isotopic Studies ◽  
The Mean ◽  
East West

AbstractThe geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were determined along an east-west transect through central Greenland. This study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature measurements m 17 steam-drilled boreholes along the eastern part of the transect. The firn temperatures at 15 m depth range from -31.6°C at Dome GRIP (3230 m a.s.l.) to -11.4°C at Caecilia Nunatak (eastern ice margin at 1600 m a.sl.) and -18°C at T05 (near the western ice margin at 1900 m a.s.l.). The temperature/altitude gradient changes from -0.7°C (100 m)−1in the ice divide region to -1.1 °C (100 m)−1in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG line is -0.7° C lat−1The average annual accumulation decreases significantly from the west (~47 cm a−1water equivalent at T05) towards the ice divide (20–25 cm a−1water equivalent from T99 to T43). Accumulation rates are constantly low east of the ice divide (−23–17 cm a−1water equivalent), thus dividing central Greenland into two climatologically different regions. The average δ18O and δD values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. ∂18O/∂Tm= 0.69%ₒ °C–1Different regression lines for the western and eastern part, however, should be applied. Unlike the mean annual temperature, the isotopic minimum along the EGIG line lies east of the ice divide. This geographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering Greenland from the west. The deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the EGIG line, suggesting equal contributions from vapour-source areas of the water precipitated over central Greenland.

scholarly journals Glacio-meteorological and isotopic studies along the EGIG line, central Greenland

1995 ◽  
Vol 41 (139) ◽  
pp. 515-527 ◽  
Author(s):  
H. Fischer ◽  
D. Wagenbach ◽  
M. Laternser ◽  
W. Haeberli
Keyword(s):  
Geographical Distribution ◽  
Accumulation Rate ◽  
Western Slope ◽  
Mean Annual Temperature ◽  
Depth Range ◽  
The West ◽  
Altitude Gradient ◽  
Isotopic Studies ◽  
The Mean ◽  
East West

AbstractThe geographical distribution of firn temperature, annual accumulation rate as well as deuterium and oxygen-18 content in the firn were determined along an east-west transect through central Greenland. This study is based on isotopic and chemical analyses of shallow firn cores at 18 sites along the EGIG line and high-precision firn-temperature measurements m 17 steam-drilled boreholes along the eastern part of the transect. The firn temperatures at 15 m depth range from -31.6°C at Dome GRIP (3230 m a.s.l.) to -11.4°C at Caecilia Nunatak (eastern ice margin at 1600 m a.sl.) and -18°C at T05 (near the western ice margin at 1900 m a.s.l.). The temperature/altitude gradient changes from -0.7°C (100 m)−1 in the ice divide region to -1.1 °C (100 m)−1 in the eastern part of the dry-snow zone. The temperature/latitude gradient in the central part of the EGIG line is -0.7° C lat−1 The average annual accumulation decreases significantly from the west (~47 cm a−1 water equivalent at T05) towards the ice divide (20–25 cm a−1 water equivalent from T99 to T43). Accumulation rates are constantly low east of the ice divide (−23–17 cm a−1 water equivalent), thus dividing central Greenland into two climatologically different regions. The average δ18O and δD values along the whole EGIG line reflect the well-known temperature-dependence for Greenland very well (e.g. ∂18O/∂Tm = 0.69%ₒ °C–1 Different regression lines for the western and eastern part, however, should be applied. Unlike the mean annual temperature, the isotopic minimum along the EGIG line lies east of the ice divide. This geographical distribution supports the choice of different water-vapour trajectories in central Greenland for the west and for the east. Significant parts of the water precipitated over the western slope are attributed to cyclonic systems entering Greenland from the west. The deuterium excess shows no significant geographical trend but a uniform seasonal variation at all sites along the EGIG line, suggesting equal contributions from vapour-source areas of the water precipitated over central Greenland.

scholarly journals Glaciological Reconnaissance of an Ice Core Drilling Site, Penny Ice Cap, Baffin Island

1984 ◽  
Vol 30 (104) ◽  
pp. 3-15 ◽  
Author(s):  
G. Holdsworth
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Surface Air Temperature ◽  
Tritium Concentration ◽  
Mean Annual Temperature ◽  
Climatic Data ◽  
Baffin Island ◽  
The Core ◽  
Ice Cap ◽  
The Mean

AbstractA site situated close to the main divide of the Penny Ice Cap, Baffin Island was occupied in 1979 for the purpose of determining the suitability of this ice cap for providing proxy climatic data and other environmental time series for a span of 104 a. A 20 m core was extracted and analysed for stable oxygen isotopes, tritium concentration, pH, electrolytic conductivity, major ion concentrations, and particulate concentration. An adjacent dedicated shallow core was analysed for pollen content to determine if a significant seasonal variation in the pollen rain existed. From these measurements, and from the observations made on the stratigraphic character of the core, the mean net accumulation rate over the approximately 30 year period covered by the core is found to be about 0.43 m water equivalent per year. This is in agreement with a single value determined 26 years earlier at a nearby site (Ward and Baird, 1954). The mean annual temperature in the bore hole was found to be close to −14.4° C, possibly some 2–5 deg warmer than the expected mean annual surface air temperature at the site. This difference is due to the expulsion of latent heat upon freezing of melt water at depth in the snow-pack which gives rise to the many ice layers observed in the core. The percentage thickness of ice layers per year may be correlated with summer temperatures.Total ice depths were measured using a 620 MHz radar echo-sounder. In the vicinity of the divide, over an area of 1 km2, the ice depths vary from about 460 to 515 m. These values compare favourably with values determined from an airborne radar depth-sounding flight carried out over the ice cap by a joint U.S.–Danish mission operating out of Søndre Strømfjord, Greenland. The data suggest that the ice-cap divide would be a worthwhile location to deep core drill with an expected useful coverage of at least the Holocene period.

Photo-electric Hβ and uvby photometry

1966 ◽  
Vol 24 ◽  
pp. 170-180
Author(s):  
D. L. Crawford
Keyword(s):  
Narrow Band ◽  
Line Strength ◽  
Interference Filter ◽  
B Stars ◽  
Relative Line ◽  
The Mean ◽  
F Stars ◽  
Two Parameters ◽  
Filter Photometry ◽  
The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

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