Main principle: seasonally controlled entities

[pbuttigieg]

In the examples below, we see that many glacial material entities and processes are seasonally determined.

@Garybc added an annual/seasonal cycle node to our mind map, presupposing this.

It's clear that this is going to be a central theme in the glacial lifecycle, so we should prep some discussion and thoughts in this issue.

ENVO has some preliminary semantics for seasons, the processes that generate them, and a few instances we can reuse or revise. The axioms for seasonal snow patch and seasonal melting process may be of interest.

Term	Def	Source
Summer ablation	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-balance measurements by the glaciological method generally measure summer mass balance and not summer ablation.	Cogley et al. IACS-UNESCO Glacier Mass Balance 2011
Summer accumulation	Accumulation integrated over the summer season. Part or all of summer accumulation may be lost by ablation before the end of the summer season.	Cogley et al. IACS-UNESCO Glacier Mass Balance 2011
Summer minimum extent	The permanent ice zone that remains in summer after all melting has occurred.	NSIDC accessed 2016
Summer season	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-accumulation 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.	Cogley et al. IACS-UNESCO Glacier Mass Balance 2011
Summer surface	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 summer 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.	Cogley et al. IACS-UNESCO Glacier Mass Balance 2011
Summer-accumulation type	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 relatively stable throughout the year. This is typical of high-altitude, low-latitude glaciers with a summer precipitation maximum.	Cogley et al. IACS-UNESCO Glacier Mass Balance 2011

[Garybc]

Glaciers are transformed by certain processes but the way that most definitions discuss this (Summer ablation for example) it less what actually happens in a process (like effect of sunlight as part of Summer ablation) than the mass effect of ice loss that results from the mic of processes.

The quality/quantity of these processes, like melting, are affected by season and location - both latitude and altitude.