Incoming longwave radiation at 47 m

Half-hourly incoming (downwelling) longwave radiation at 47 m on the CH-LAE tower, 2005-2025, exported as measured. The file is 06_METEO_LW_IN_2005-2025 (parquet and CSV): 355,872 records on a continuous 30-minute middle-timestamp index (named TIMESTAMP_MIDDLE in the file) in local time (UTC+1, no daylight saving), from 2005-09-14 00:15 to 2025-12-31 23:45.

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:

06_METEO_LW_IN — builds the product: the merge of the two screenings, the 2012 corrections, the identification of the instrument from the logger programs and the maintenance record, and the measurement of the calibration change described below.
01_METEO_SW_IN — the other channel of the same radiometer. It establishes the instrument’s identity and dates its replacement, and it is the reference for what the January 2016 and December 2021 hardware changes did to the shortwave side.
02_METEO_TA — the air-temperature product, which notebook 06 uses as its only diagnostic driver.
Meteo_Product_Chain — where this product sits in the chain.

The record changes level on 7 June 2016

This series is not homogeneous. Until 7 June 2016 the pyrgeometer’s signal was converted with the calibration factor of the pyranometer in the same instrument, 10.03 instead of 12.83 µV/W/m². On that date the site’s logger program was corrected, and everything recorded before it reads too low.

The size of the error is not a constant. It is proportional to the difference between the value and \(\sigma T_a^4\), so it is largest under a clear sky and approximately zero under low overcast: about 9 W m^-2 in the middle of the distribution and up to some 22 W m^-2 on a clear, dry night.

No correction is applied and no homogenised column is provided; the reasons are under Known limitations. Filter on FLAG_LW_IN_T1_47_1_SOURCE before comparing the two eras, and treat any trend computed across mid-2016 as containing this change.

Columns

Table 1: Columns of 06_METEO_LW_IN_2005-2025.

column	unit	description
`LW_IN_T1_47_1`	W m^-2	Incoming longwave radiation, as measured. Contains `NaN`.
`FLAG_LW_IN_T1_47_1_SOURCE`	-	Which instrument and which calibration factor produced the value. Defined at every record.

There is no ISFILLED flag, because nothing is filled: a non-null value is a measurement and a NaN is a real gap. PA is the only other meteo product exported this way.

`FLAG_LW_IN_T1_47_1_SOURCE`

Table 2: Provenance codes and their record counts over the 350,969 measured records.

code	meaning	period	records	share
0	CNR4, its own calibration factor	from 2022-01-07	69,724	19.9 %
1	CNR1 at 12.83 µV/W/m², the pyrgeometer’s own factor	2016-06-07 to 2021-12-14	96,037	27.4 %
2	CNR1 at 10.03 µV/W/m², the pyranometer’s factor — reads low	before 2016-06-07	184,104	52.5 %
3	changeover, era undetermined	2021-12-15 to 2022-01-06	1,104	0.3 %

Code 3 marks the three weeks between the installation of the CNR4 and the arrival of its own constants in the logger program, during which the new instrument was read through the old instrument’s factor. Neither the maintenance record nor the data can assign this interval to either side.

Coverage

The measurement begins on 2005-09-14 13:15, when the pyrgeometer channel was wired to the tower logger; there is no longwave record before that date and none is reconstructed. Of the 355,872 records, 350,969 carry a value (98.6 %).

The gaps are short. There are 998 of them; 977 are one hour or shorter and only eight exceed a day. The longest, 20.6 days, runs from 1 to 21 January 2016, the site-wide outage during which the tower logger was replaced, which PA shares record for record.

Table 3: The two years in which measured coverage falls below 95 %. Every other year of 2006-2025 is at least 95 % measured.

year	measured	why
2012	92.3 %	logger clock error, power-supply failure and storm damage
2016	94.3 %	the January outage during which the logger was replaced

The 2012 faults are the largest interruption inside the measured period. A logger clock error shifted one block of August 2012 by 15.5 hours; a tower power-supply failure in late July and August, and storm damage in late October and November, left records that were removed. Unlike the other tower variables, LW_IN shows no internal sign of either fault: it has no independent reference that could reveal a level error, and the removal therefore rests on the documented, logger-wide fault rather than on evidence from this series. Notebook 06 states this and removes the periods anyway, as the conservative choice.

What the values are

The exported numbers are downwelling longwave irradiance, median 315.85 W m^-2 and range 135.45 to 441.78 W m^-2. A pyrgeometer’s voltage measures the net exchange between the sky and the instrument’s own body, which at this site is roughly -50 W m^-2; the downwelling flux is that net signal plus the instrument’s own emission. That term is already included in every value in this file. A reader who assumed the raw converted voltage would misread the file by some 370 W m^-2.

Known limitations

The record is not homogeneous across 7 June 2016. The pyrgeometer’s calibration factor was corrected on that date, and values before it read low by roughly 17 % of the difference between the value and \(\sigma T_a^4\). This is more than half the record. It is not corrected, for a specific reason: undoing it requires splitting each stored value back into the instrument’s own emission and its net signal, which needs the radiometer’s body temperature, a channel this product does not read and one whose treatment in the processing chain that produced the earlier values cannot be verified from the files available. Rescaling with air temperature as a proxy would import an unverified model of that chain into the exported numbers. The SOURCE flag marks the affected era instead.
The record also changes across December 2021, and the cause is not established. The radiometer was replaced (CNR1 to CNR4) on 14 December 2021, and the screening software changed from mst to diive at the turn of the year. The two fall on the same date and cannot be separated, and there is no reference against which either could be tested. What the data show is a change of about 11 % in the clear-sky part of the signal, roughly half the size of the June 2016 change, which accounts for most of the 6.5 W m^-2 that separates the two periods once the temperature difference between them is removed. It is equally consistent with a change in the instrument, with the change of screening, and with the warming and moistening of the lower atmosphere that has been moving the same statistic since about 2017. Nothing is corrected. Analyses crossing that date should allow for a change of this order, and the SOURCE flag separates the two instruments.
The January 2016 acquisition change did not move this series. It is recorded here because the same changeover moved TA_T1_47_1 by 1.3 °C, and because it is easy to confuse with the June date five months later. The logger program installed at the changeover applies the same conversion as the programs before it, and the four months between the two 2016 dates behave like an ordinary year.
The series contains gaps and is not gap-filled. Code that assumes a complete series will break or silently propagate NaN. SW_IN, TA and PPFD_IN are complete; this product is not.
There is no independent reference for this variable at the site. MeteoSwiss Lägern carries no longwave channel, NABEL has no pyrgeometer, and the below-canopy sensor installed in 2024 measures a different quantity. Every statement above therefore rests on physics, the relation between longwave radiation and air temperature, rather than on a second instrument, and the evidence is correspondingly weaker than for SW_IN or TA. Where it does not reach far enough to identify a cause, notebook 06 says so.
Absolute accuracy is limited by the calibration that was applied. Both eras of the CNR1 convert the pyrgeometer with a single factory constant and no correction for the instrument’s own dome. The two radiometer channels of the successor instrument differ by 28 % in sensitivity, which is the scale of the error the June 2016 entry removed; what remains after it is the ordinary field uncertainty of an unventilated pyrgeometer, which is larger than for the shortwave channel of the same instrument.