hobos

	Snow/ice interface



Home	Optics	Mass	Snow	Aerial	Logs

Small Hobo-XT data loggers (Hobo XT manufactured by Onset Computer Corp.), were installed at 30 stakes near the SHEBA camp and at Baltimore to measure the variation in temperature at the snow/ice interface. Each HOBO logger had a thermistor placed at the interface, with the data logger in a Nalgene jar taped to the snow/ice depth stake. The instruments were installed in late-October, over a period of several days. They recorded data continuously until about 25 April, at which time their memory storage was full. On the 28 and 29 April, the loggers were dumped and relaunched, leaving a data gap of about 4 days. They then ran until freeze-up. Tht table indicates the location of each Hobo by stake and site name, and the snow depth (n=3) on 28-29 April.

Thermistors were capable of measuring temperatures between -37° and +46°C with an accuracy stated by the manufacturer to range between 0.5 and 1%. This translates to uncertainties of up to ±0.5°C for recorded temperatures. To be conservative, we think the uncertainty should be considered ±1°C. Temperatures lower than -37°C are recorded as -37°C, so periods of extreme cold are represented as "flat" spots in the temperature record.

The data loggers recorded the time each datum was collected in Alaska Standard Time. A worst-case timing error due to data logger drift of about 45 minutes was calculated for the longest period of operation (6 months) based on the manufacturer's specifications. Logger times were reset to computer time during the site visit, at which time uncertainties due to drift were returned to zero. Examination indicated that all loggers were synchronous to ±1.5 hours, and as this is less than the timing accuracy, all data are associated with a single set of time-date values. Care should be exercised in interpreting time delays between sites that are less than 4 hours. Individual thermistors may have been alternately buried by snow and excavated by the wind, giving rise to large relative variations in temperature between thermistors. Once the thermistors were exposed (temperatire > 0°C), temperatures may be unreliable (see data from late May through July, 1998.

Hobo data logger in plastic bottle mounted on an ablation stake. The thermistor probe was placed at the snow-ice interface.

Selected time series of snow/ice interface temperature. Note the large differences during winter.

Summary of snow/ice interface sensor locations.

Hobo	Ablation stake	Site	Depth 1	Depth 2	Depth 3
2	81	Ridge	50	48	49
3	79	Ridge	20	21	20
4	41	Ridge	44	46	43
5	31	Ridge	88	83	89
6	75	Ridge	57	52	54
7	77	Ridge	14	14	14
8	55	Ridge	58	55	49
9	47	Ridge	25	25	32
10	58	Ridge	6	6	6
11	26	Ridge	74	74	73
12	70	Ridge	36	38	36
13	73	Ridge	48	49	31
14	21	Ridge	41	41	43
15	57	Ridge	61	63	63
16	133	Baltimore	44	45	45
17	29	Ridge	11	11	11
18	148	Baltimore	33	33	34
19	9	Ridge	35	34	37
20	32	Ridge	71	58	70
21	142	Seattle	48	48	50
22	37	Baltimore	65	67	69
23	63	Baltimore	52	55	56
24	11	Baltimore	80	81	83
25	51	Baltimore	20	19	18
26	39	Seattle	39	39	39
27	44	Seattle	8	9	8
29	7	Seattle	43	43	43
30	34	Seattle	35	35	37