Ablation integrated over the summer season. Summer ablation is not the same as summer mass balance. It is generally more negative because some of the lost mass may be offset by accumulation. Mass-bala
nce measurements by the glaciological method generally measure summer mass balance and not summer ablation.
A type of glacier on which the regional seasonality results in extrema of ablation rate and accumulation rate at roughly the same time. On a glacier of summer-accumulation type, mass balance remains r
elatively stable throughout the year. This is typical of high-altitude, low-latitude glaciers with a summer precipitation maximum.
The time span from the end of the winter season to the end of the mass-balance year. The length of the summer season may vary greatly from year to year. The term is best suited to glaciers of winter-a
ccumulation type. In the stratigraphic system the summer season starts when the glacier has attained maximum mass and ends when the glacier has attained minimum mass. In the floating-date system and the fixed-date system, the mass is not necessarily at its Annual maximum or minimum when the summer season starts or ends.
The moment in the northern hemisphere when the Sun attains its highest declination of 23°26' (or 23°.44) with respect the equator plane. It happens when the Earth's axis is orientated directly toward
the Sun, on 21 or 22 June. During the northern solstice the Sun appears to be directly overhead at noon for places situated at latitude 23.44 degrees north, known as the tropic of Cancer. The summer solstice can occur at any moment during the day. Two successive summer solstices are shifted in time by about 6 h. The summer solstice in the northern hemisphere is the winter solstice in the southern hemisphere.
The surface formed at the time of minimum Annual mass at each point on the glacier, marking (in the stratigraphic system) the end of one mass-balance year and the start of the next. In general the sum
mer surface is diachronous. For example, when the higher reaches of a glacier start to gain mass, the lower parts may still be ablating. The summer surface is the surface on which the first snow of the new balance year falls. It is easily detectable when it consists of glacier ice, which now includes superimposed ice added during the previous balance year. In the firn area it is recognizable as a well-marked crust, that is, a thin, relatively strong layer with a density near that of ice, and sometimes also (or instead) as a layer of depth hoar at the base of the current year's accumulation. The crust typically originates by recrystallization of the surface snow in late summer to form glaze. It may also be marked by an accumulation of sediment or wind-blown dust. It can be difficult to detect when melting and snowfall alternate during the transition between the ablation season and the accumulation season. In some mass-balance programmes the summer surface is 'labelled' in the vicinity of stakes with a distinctive material, such as sawdust, during a visit late in the ablation season.