Shortwave Radiation

Shortwave radiation is the main driver of snow and ice melt in most environments. Incoming solar radiation is absorbed and scattered as it traverses the gauntlet of atmospheric gases and aerosols (suspended particles such as water droplets, ice crystals, and dust). The processes of absorption and scattering depend on the wavelength of the electromagnetic radiation and the size of the obstacle (gas or aerosol). Similarly, backscatter (reflection) from ice crystals is also wavelength dependent,...

Snow albedo

The influence of snow and ice in the climate system stems largely from their high albedo. Shortwave radiation is backscattered from snow and ice, with the reflectivity strongly dependent on wavelength. Neglecting this complexity for now, the broadband surface albedo can be defined from the ratio of reflected to incoming shortwave radiation, a QS QS. A range of albedo values for snow and ice is given in table 2.1. Albedo is highly variable, spatially and temporally, so it is not recommended to...

Glacier and ice sheet volume

Glacier area can be well mapped from satellite imagery and aerial photographs, but global ice volume is more difficult to estimate. Mapping of ice thickness requires surface or airborne radar surveys. Electromagnetic wave frequencies of 5-50 MHz are typically used for glacier depth sounding, as these relatively low frequencies limit signal attenuation and allow penetration of radar pulses through several hundred meters of glacier ice. Resolution at these frequencies is of the same order as the...

Snow And Ice Albedo

Snow and ice are the most reflective natural surfaces on the planet, exceeded only by clouds in their influence on planetary albedo. This reduces the net solar radiation that is available to warm the Earth, lowering the mean annual temperature of the planet. The cryosphere also introduces regional and seasonal variability in the absorbed solar radiation that is available. Surface albedo effects of the cryosphere have the greatest impact on regional and local climate through cooling and through...

Snow in the Atmosphere

The physical properties of snow define and shape its influence on climate and society. Temperatures in the middle and upper troposphere are below 0 C, so ice crystals can be found everywhere in the global atmosphere. As discussed in chapter 2, mixed clouds below this temperature consist of a blend of water vapor, ice crystals, and supercooled water droplets. Once nucleated, ice crystals grow through deposition of water vapor. Saturation vapor pressure on the surface of rounded water droplets is...

Internal Deformation

To solve the momentum balance, ice sheet stresses need to be expressed as velocity fields, via a constitutive relation for ice. The rheology of polycrystalline glacier ice is well studied in laboratory and field environments, which reveal that ice deforms as a nonlinear viscous fluid. The original form of the flow law, proposed by John Glen and John Nye in the 1950s, is broadly supported by field studies of tunnel and borehole deformation, as well as observations and modeling of large-scale ice...

Characteristics of sea ice

Sea ice forms from freezing of seawater. Dissolved salts predominately NaCl, but many other ions as well depress the freezing point of seawater by approximately 0.054 C ppt-1. For mean ocean water with a salinity of 34.5 ppt, sea ice forms at -1.86 C. Polar waters are often fresher than average seawater, due in part to limited evaporation. For salinities of 25 ppt and 30 ppt, water freezes at -1.35 c and -1.62 c, respectively. Figure 5.1. A variety of Arctic sea-ice types and seasons. (a)...

Density Of Snow And

The geometric arrangement of this lattice structure is spacious, giving water the most unusual property of having a solid phase that is less dense than its liquid phase. At 0 C, water has a density of 1000 kg m-3, whereas pure ice (Jh) has a density of 917 kg m-3. Ice floats in its own melt, one of few substances to do so. Diamonds, germanium, gallium, and bismuth, all structurally similar to ice, also float in their own liquid. Imagine the sight of sunlight sparkling off of a diamond-berg in a...

Internal Energy Balance In Snow And

The internal temperature evolution in a snowpack or a thickness of ice (e.g., a slab of sea ice or the interior section of permafrost or a glacier) is governed by conservation of energy. This is described by the first law of thermodynamics, balancing the rate of change of internal energy with the fluxes and sources of energy in the snowpack. Conductive heat transfer is the main process that governs the rate of change of internal energy in the near-surface layer. In addition, shortwave radiation...

Permafrost Thermodynamics

Like lake, river, and sea ice, permafrost forms due to subzero surface temperatures that induce freezing from above. Surface tension effects retain some liquid water content to low temperatures (-10 C or less), particularly in fine sediments such as clays and silts. However, the 0 c isotherm in the ground generally represents the freezing front the depth at which the phase change begins and ice can be found in the soil or rock matrix. Seasonal ground frost is widespread in midlatitudes and high...

Longwave Radiation

Longwave radiation is also known as infrared, thermal, or terrestrial radiation. It is electromagnetic energy in the spectral band from roughly 3 to 100 mm. Earth surface temperatures produce emissions in this range, with peak terrestrial radiation occurring at a wavelength of about 10 mm. Spectrally integrated longwave radiation can be estimated from the Stefan-Boltzmann equation, Ql eoT4, where e is the thermal emissivity, o is the Stefan-Boltzmann constant, 5.67 X 10-8 W m-2 K-4, and T is...

Mass Balance processes

Glaciers have relatively simple requirements to be viable snow accumulation must exceed ablation. Snow accumulation occurs primarily as meteoric snowfall (derived from atmospheric precipitation), but snow can also accumulate at a site through wind deposition or avalanch-ing. Ablation refers to the loss of snow and ice through melting, sublimation, wind erosion, and calving, a process whereby slabs of ice at the glacier margin mechanically fracture and detach from the main ice mass. This is an...

Energy BuFFER

Melting snow and ice requires a great deal of energy. These phase changes consume sensible heat and radiative energy that would otherwise go into warming up a region. The opposite effect attends the fall freeze-up latent energy is released to the atmosphere, lakes, rivers, oceans, and soil as ice forms from water and vapor. This delays the seasonal decrease in temperatures. Overall then, latent energy exchanges within the seasonal cryosphere act as a thermal buffer, similar to the way in which...

Governing Equations for Glacier Dynamics

Similar to models of atmosphere, ocean, and sea-ice dynamics, the flow of glaciers and ice sheets is mathematically described from the equations for the conservation of mass, momentum, and energy. For a point on the glacier with ice thickness H, the vertically integrated form of the conservation of mass is Figure 6.3. Schematic of glacier flow mechanisms. The surface velocity us ub + ud (s). Basal velocity is the sum of deformation of underlying sediments and decoupled sliding at the ice-bed...

Pleistocene Glacial Cycles

The world changed again beginning at about 2.5 Ma. Figure 9.1b illustrates the onset of the Pleistocene glacial cycles at this time, a turbulent period in Earth history that continues to this day. The planet has experienced more than 40 glacial-interglacial episodes during this period, with ice sheets intermittently flooding large expanses of the Northern Hemisphere continents. As seen in Figure 9.1b, these cycles increased in magnitude over the past million years, indicating that glaciations...

Geography Of Earths Snow And

Perennial ice covers 10.8 of Earth's land surface table 1.1 and figure 1.1 , with most of this ice stored in the great polar ice sheets in Greenland and Antarctica. Smaller glaciers and icefields are numerous the global population is estimated at more than 200,000 but these ice masses cover a relatively small area of the landscape. An additional 15.4 of Earth's land surface is covered by Area and Volume of the Global Cryosphere Area and Volume of the Global Cryosphere Note Sea ice data is from...