Modified

30 July 2026

Precipitation at 47 m

Half-hourly precipitation from the rain gauge at 47 m on the CH-LAE tower, 2004-2025. The file is 08_METEO_PREC_GAPFILLED_2004-2025 (parquet and CSV): 385,728 records on a continuous 30-minute middle-timestamp index (named TIMESTAMP_MIDDLE in the file) in local time (UTC+1, no daylight saving), from 2004-01-01 00:15 to 2025-12-31 23:45. Values are sums over each half hour in mm, on the gauge’s 0.1 mm tipping-bucket grid. Divide by 0.5 h for a rate.

The interactive dashboard summarises the product on one page: coverage and provenance, seasonality, distributions, extremes and trends, with a table view behind every chart. It is standalone and works offline.

Method, evidence and checks:

ImportantWhich column to use

The measured column is not homogeneous across mid-2018, when the gauge moved from one acquisition system to another. Annual totals average 830 mm before the change and 1,003 mm after it.

  • Inside one era, use PREC_TOT_T1_47_1, which is what the gauge recorded.
  • Across mid-2018, use PREC_TOT_T1_47_1_HOMOGENIZED. A total spanning the change taken from the measured column is dominated by the acquisition change rather than by the weather.

Neither column is complete: 0.58 % of records are NaN, all of them before June 2014, and a missing record is not a dry one.

Columns

Both value columns are NaN at the same records. The flags apply to either, since the homogenisation changes values and not provenance.

Table 1: Columns of 08_METEO_PREC_GAPFILLED_2004-2025.
column unit description
PREC_TOT_T1_47_1 mm (30 min)-1 Precipitation as the gauge recorded it, with the fillable gaps taken from Ehrendingen. Inhomogeneous across mid-2018.
PREC_TOT_T1_47_1_HOMOGENIZED mm (30 min)-1 The same series with the pre-2018 era rescaled onto the level of the later era. A derived estimate, not a measurement.
FLAG_PREC_TOT_T1_47_1_SOURCE - Which acquisition chain and screened record a measured value came from.
FLAG_PREC_TOT_T1_47_1_ISFILLED - Whether the record is a measurement at all.

The flags are complementary: ISFILLED == 0 exactly where SOURCE > 0, and the value is NaN exactly where ISFILLED == 2.

FLAG_PREC_TOT_T1_47_1_SOURCE

Table 2: Acquisition eras, the screened record each came from, and their record counts.
code acquisition and screening period records
0 not measured at the tower: filled or missing scattered, 2004-05-04 to 2025-09-26 3,156
1 EMPA acquisition, diive screening 2004-01-01 00:15 to 2018-05-28 23:45 250,327
2 changeover in progress, era undetermined 2018-05-29 00:15 to 2018-08-07 23:45 3,408
3 ETH logger, diive screening 2018-08-08 00:15 to 2018-12-31 23:45 7,008
4 ETH logger, MeteoScreeningTool screening 2019-01-01 00:15 to 2020-01-02 00:45 16,811
5 ETH logger, diive screening 2020-01-02 01:15 to 2025-12-31 23:45 105,018

Codes 3, 4 and 5 are one acquisition chain, split only by which screened record delivered the values; where records 4 and 5 overlap they agree value for value over two full years. Select SOURCE >= 3 for the homogeneous later series and SOURCE > 0 for every gauge measurement. Code 2 covers the ten weeks of the changeover, which two maintenance entries bracket and 19 rain days cannot resolve.

FLAG_PREC_TOT_T1_47_1_ISFILLED

Filter on == 0 for measured records. Code 1 is another gauge’s measurement, rescaled; code 2 is a gap that could not be filled.

Table 3: Fill codes and their record counts.
code meaning records share
0 measured at the tower 382,572 99.18 %
1 filled from MeteoSwiss Ehrendingen, rescaled by a monthly factor 932 0.24 %
2 still missing: no sub-daily reference exists 2,224 0.58 %

The 932 filled records add 56.4 mm and only 96 of them are wet; 759 of them fill the 16-day outage of November 2019. The 2,224 unfillable records all lie before 2014-06-04 10:15, because Ehrendingen has no sub-daily data before September 2014.

The 2018 acquisition change

One instrument measured throughout, a Lambrecht 15188H at 47 m. In mid-2018 it was moved from EMPA’s acquisition system to the ETH CR1000 logger, and the recorded amounts rise by about a fifth. The break is in the measurement chain, not in the instrument.

The later era is the one to trust. Against every MeteoSwiss precipitation station within 21 km the early era reads low, at ratios of 0.74 to 0.91, while the later era agrees with the network at 0.91 to 1.05. Against the ensemble’s elevation gradient the early era sits 25 % below what a gauge on this ridge should catch and the later era 10 % below, where roughly 10 % is ordinary wind under-catch for an exposed ridge top.

PREC_TOT_T1_47_1_HOMOGENIZED lifts the early era onto the later one with a factor per calendar month, fitted against those stations. The factors run from 1.07 to 1.44, equivalent to 1.21 applied uniformly, and they bring the mean annual total of the complete early years from 830 mm to 991 mm against 1,003 mm for the later era. The later era is copied through unchanged. Neither era is absolutely calibrated: the correction makes the record self-consistent across 2018 without removing the under-catch both eras carry.

No second break in 2016

January 2016 moved three other tower variables when the datalogger was replaced, and a program change that June left more than half the longwave record reading low. Precipitation is unaffected, because the gauge was not on that logger; it stayed on EMPA’s acquisition until 2018. No surviving tower program records the gauge at all, and the 20.6-day outage that pressure and longwave both suffer while the logger is replaced is absent here, with all 988 half-hours measured. The catch ratio against the regional stations confirms it at both dates, and finds nothing at any later boundary either, including the change of screening tool in January 2020.

Known limitations

  • Neither column is absolutely calibrated, and both read low. Against the regional stations’ elevation gradient the later era sits about 10 % below what a gauge on this ridge should catch, which is ordinary wind under-catch for an exposed ridge top. The homogenisation lifts the early era onto the later one and deliberately stops there, so that 10 % remains in both columns. A total from this product is what the gauge caught, not what fell.
  • Winter totals are biased low, and the bias changes at 2018. The gauge misses snow as it falls and releases part of it days later on melt, so winter sub-daily timing is unreliable in both eras. On days below 2 °C the catch ratio averages 0.62 before 2018 and 0.56 after, but individual winters vary by more than that. The maintenance record has the heating disconnected on 8 August 2018, the day the gauge was rewired, still inactive in January 2024, and a new transformer fitted in July 2024; none of the three dates shows up in the data, so nothing is corrected. A winter total spanning 2018 mixes the acquisition change with a change in snow catch, which is why the largest monthly factors are the winter ones.
  • The homogenisation leaves light rain untouched. Homogenised values are rounded back onto the 0.1 mm grid, and a small amount times a factor of 1.07 to 1.44 often rounds back to itself. So 9,146 of the 20,801 wet half-hours in the early era are identical in both columns, carrying 11 % of its rainfall: every 0.1 mm record, 55 % of the 0.2 mm records, 28 % of the 0.3 mm ones, and nothing above 1 mm. A count of wet half-hours or a light-rain intensity statistic is therefore not homogenised by that column, and the factor delivered overall is 1.19 rather than the 1.21 fitted, which is part of why the homogenised early era lands 1.2 % below the later level rather than exactly on it.
  • Filled records are good for sums, not for timing. A filled value is the Ehrendingen gauge’s measurement, 3.8 km away and 260 m lower, rescaled. On synthetic gaps the summed rainfall is right to within 2.2 % at every gap length, but the median error on one gap’s total is 14 % for a two-week gap and about 35 % for a one-hour gap, so short gaps are the unreliable ones. At half-hourly resolution the correlation is 0.7, about a quarter of the half-hours a fill marks wet were dry at the tower, and about 30 % of wet half-hours are missed.
  • GAPFILLED in the filename does not mean complete. Unlike SW_IN, TA and PPFD_IN, this product still contains NaN, and code that assumes otherwise will break on it or propagate NaN silently.
  • 2008 is the only badly incomplete year, at 93.2 % coverage. A 24.6-day outage in May and June falls inside the unfillable period; Ehrendingen recorded 58.5 mm over that window. Every other year carries a value for at least 98.3 % of its records.
  • Zeros are data. 91.2 % of records carrying a value are exactly 0, the correct value for no rain rather than a sentinel. The largest half hour in the record is 27.7 mm, on 2023-07-12.
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