What does the `pressure_level` field do when downloading from the single levels dataset?

Hello, 

I have a script that partitions a data requests into smaller chunks. I'm downloading data from this data source (hourly single levels Era5 data; https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-single-levels?tab=overview). Somehow, I was able to specify `pressure_level=n` (where n is a pressure level listing; ERA5: data documentation#Levellistings) in my request. No error was thrown during my downloads with the Copernicus client. However, I'm not sure how to interpret the variables that are downloaded at pressure levels outside of 1000. Can anyone explain what data I have downloaded? 


For reference, here is the description of the data I've requested (in Python's ConfigParser format. Partitioning logic is handled elsewhere, requests are partitioned by (date x variable x pressure_level)): 

dataset=reanalysis-era5-single-levels
product_type=reanalysis
format=netcdf
variable=
100m_u_component_of_wind
100m_v_component_of_wind
10m_u_component_of_neutral_wind
10m_u_component_of_wind
10m_v_component_of_neutral_wind
10m_v_component_of_wind
10m_wind_gust_since_previous_post_processing
instantaneous_10m_wind_gust
2m_dewpoint_temperature
2m_temperature
geopotential
high_cloud_cover
ice_temperature_layer_1
ice_temperature_layer_2
ice_temperature_layer_3
ice_temperature_layer_4
instantaneous_10m_wind_gust
low_cloud_cover
maximum_2m_temperature_since_previous_post_processing
mean_sea_level_pressure
mean_wave_direction
mean_wave_period
medium_cloud_cover
minimum_2m_temperature_since_previous_post_processing
significant_height_of_combined_wind_waves_and_swell
skin_temperature
snow_density
surface_pressure
total_cloud_cover
total_precipitation
pressure_level=1/2/3/5/7/10/20/30/50/70/100/125/150/175/200/225/250/300/350/400/450/500/550/600/650/700/750/775/800/825/850/875/900/925/950/975/1000
date=2021-08-20/to/2018-01-01/by/-3

# Once an hour for 24 hours, see https://confluence.ecmwf.int/pages/viewpage.action?pageId=118817378
time=0000/to/2300/by/0100
area=45/-103/33/-92

Hi,

the pressure level data are available from this source:

https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-pressure-levels?tab=form

where dataset=reanalysis-era5-pressure-levels.

If dataset=reanalysis-era5-single-levels is used in the API script, the extracted data file will contain ERA5 single level data only.

It is advised to request one month at the time to have an efficient request and use the web interface of the relevant dataset and the 'Show API request' button to get the code to construct correct CDS API scripts. Additional keywords in the request for single level data (such as 'pressure_level') would be ignored.

Please be aware that parameters on pressure levels are different from the single level data.


Best regards

Michela