Several empirical equations to possess firn densification was received,offered firn porosity as a function of excess stress. In the step onest formula, thereduction ratio regarding porosity when you look at the firn is assumed become proportional on the expanding ratioof excess tension as well as the mth energy away from the porosity. This new porosity exponent yards will be next to -dos, to has a just-fit with fourteen depth-occurrence users fromGreenland and you can Antarctica. In the 2nd picture, the fresh avoidance proportion from porosity wasassumed to increase proportionally to your increment off overload tension and you may thenth power of the porosity. The most sufficient viewpoints of your exponent consist of -step 1 to just one. It has been advised you to definitely firn thickness, determined mainly of the overburdenpressure and you can firn temperature, contribute to a lower life expectancy education.
The fresh sales means of firn in order to ice is among the extremely simple subjects inside the polar frost-layer studies. A lot of theories concerning your deceased densification from firn has actually become proposed ( Source Robin Robin, 1958 Resource Schytt Schytt, 1958 Source Bader Bader, 1960, 1962 Resource Benson Benson, 1962 Anderson and you can Reference Benson Benson, 1963 Resource Kojima Kojima, 1964 Reference Gow Gow, 1975). Although not, a thorough design together with grains-repaying, sublimation/condensation, volume/ body diffusion, frost distortion and you may recrystallization processes was not securely created. The new densification process are also read empirically ( Site Robin Robin, 1958 Source Schytt Schytt, 1958 Resource Herron and you can Langway Herron and Langway, 1980 Resource Ling Ling, 1985 Reference Langway, Shoji, Mitani and you may Clausen Langway while some, 1993). Source Schytt Schytt (1958) discovered an enthusiastic empirical family anywhere between firn density together with weight out of overlying accumulated snow. Reference Herron and Langway Herron and you will Langway (1980) examined the legitimacy away from Schytt,s equation playing with 17 depth-occurrence pages regarding Greenland and you can Antarctica. Source Langway, Shoji, Mitani and you may Clausen Langway while some (1993) shown an easy family members between overload stress and you will firn occurrence
It papers focuses on obtaining a straightforward formula fora relationships ranging from overburden stress and you will firndensity from the skin into the depth away from pore romantic-from as a https://datingranking.net/sugar-daddies-usa/ny/albany/ result of the studies by Source Schytt Schytt (1958) and Langwayand other people (1993).
2 Analytical Processes
In place of with the accumulated snow densification law ( Reference Bader Bader, 1960,1962), an assumption was created you to snowfall behaves for example aperfectly plastic material. That’s, porosity, s(= (?i – ?)/ ?i) is determined merely of the overburden pressure, P, at each and every breadth peak. ?is the firn thickness and you can ?i is the ripple-100 % free frost occurrence during the -20°C (0.919.Mgm-3). When the tension P develops so you can P +dP, s minimizes to s-ds. Thereduction ratio out of porosity, -ds/s is assumed toincrease proportionally on the expanding proportion of tension, dP/P while the mth out of strength out-of s below:
Other formula try received from the assuming that the protection proportion of porosity, -ds/s increases proportionallytothe increment out-of tension, dP, together with nth fuel out-of s as follows:
Has just, Site Langway, Shoji, Mitani and you can Clausen Langway although some (1993) exhibited good linearrelation anywhere between (?i-?) dos plus(P) throughout the facial skin so you’re able to.the new depth out of pare intimate-regarding for a few internet from inside the Greenland andAntarctica. If we write the expression(?i-?)2of Langway while some (1993) to help you ((?i-?)/?i) dos , new family is actually conveyed as follows:
On the other hand, Resource Schytt Schytt (1958) recommended the second relatives ranging from firn density (?) and you can depth from the facial skin (h) far the new Maudheim Frost key,Antarctica:
step three Abilities
Depth-thickness pointers try extracted from fourteen sites from inside the Greenland and you may Antarctica given that found within the Dining table 1. The latest 10m depth firn temperatures of borehole cover anything from-54.3° so you’re able to -sixteen.4°C and annual buildup rates rangefrom 0.034 so you’re able to 0.39 yards season 1 in h2o equivalent. Thedata scatters in bulk-occurrence opinions are usually ±0.005 Mgm -step 3 of these from Conference, S25, H15, S25, G15, G6,Byrd epidermis go camping and you may Dome C. As well, thedata scatters for siteJ, webpages dos, site A good, G2, Mizuho, LittleAmerica V and you may Old Byrd Route is actually contained in this ±0.003 Mgm -3 , once the densities was indeed determined a great deal more truthfully by the a good volumetric method. The fresh reliabilityof ten yards breadth temperatures can be ±0.1°C otherwise ideal.
An attempt was made to discover the most satisfactory valuesfor yards and you can n into the Equations (1) and you will (4) utilizing the above depth-occurrence users. Depth-occurrence philosophy of thesurface on depth from which the latest occurrence try 0.80 Milligrams m step three are used for the new correlation-coefficient analysis.
Figure la suggests the results of the linearity attempt forEquation (1) having fun with additional beliefs regarding m. It is clear you to definitely correlation coefficients make large opinions to m = -2 (roentgen = 0.98). Profile 2b reveals the outcome to own Picture (4) using other values out-of n. It absolutely was unearthed that the relationship coefficients make the highest worth of n = -step one in order to + step 1 (r = 0.97 on letter = 1; r = 0.98 al letter = 0;r = 0.95 on n = 1). Therefore, we become this new followingequations, that are similar that have Equations (7) and you can (8):
Fig.1 . The fresh loved ones anywhere between opinions regarding energies and you can correlation coefficients with regards to standard deviations. Figure 1a reveals the outcomes to have meters for the Picture (1) and you can Figure 1b to have letter in Equation (4).
Fig.2 . Relations between ln(P) and you can s 2 for fourteen internet during the Greenland and you may Antarctica. P is an overload stress and you can s is the porosity from firn, where s =(?i-?)/?i.?i is the ripple-100 % free frost occurrence and you can ? is the firn density.
Figure 2 shows the relation between ln(P) and s2 for the 14 ice cores from Greenland and Antarctica. It is seenthat ln(P) and s 2 have excellent linear correlation. Correlation coefficients, linear slopes (C1),Y intercepts(C2) and degrees of freedom are summarized in Table 2. The lowest correlation coefficient at G6 is due to datavariations in the surface-firn densities.
Figure step 3 suggests this new family anywhere between P as well as in(s) forthe fourteen freeze cores. Seemingly the overburdenpressurecurves provides a bow around an occurrence off 0.50–0.sixty Mg meters -step three . The new linear-relationship study is summarizedin Dining table step 3. The newest mean relationship coefficient forEquation (10), because the shown within the Contour 3(r = 0.98), is actually thesame since suggest relationship coefficients gotten getting Formula (9) given that found inside Shape dos (r = 0.98).