Published January 18, 2025 | Version v1
Data paper Open

Enhancing the Representation of Atmospheric Water Isotopes with Higher-Resolution Global Modeling (IsoGSM4)

Authors/Creators

  • 1. NASA Goddard Institute for Space Studies
  • 2. ROR icon The University of Tokyo

Description

Pre-submission dataset created; openly accessible, but use requires permission from the authors.

IsoGSM3: Isotope-incorporated Global Spectral Model version 3 (hereafter IsoGSM-LR, standard resolution)
IsoGSM4: Isotope-incorporated Global Spectral Model version 4 (hereafter IsoGSM-HR, high resolution)

Citations
1. IsoGSM: Yoshimura, K., Kanamitsu, M., Noone, D., & Oki, T. (2008). Historical isotope simulation using reanalysis atmospheric data. Journal of Geophysical Research, 113(D19), D19108. https://doi.org/10.1029/2008JD010074

2. IsoGSM3: Bong, H., Cauquoin, A., Okazaki, A., Chang, E.-C., Werner, M., Wei, Z., Yeo, N., and Yoshimura, K. (2024). Process-based intercomparison of water isotope-enabled models and reanalysis nudging effects. Journal of Geophysical Research: Atmospheres, 129, e2023JD038719. https://doi.org/10.1029/2023JD038719

3. IsoGSM4: Bong, H. and Yoshimura, K. (2025). Enhancing the Representation of Atmospheric Water Isotopes with Higher-Resolution Global Modeling (IsoGSM4), Scientific Data. in preparation.

Point of contact
Kei Yoshimura — kei@iis.u-tokyo.ac.jp
Hayoung Bong — hayoung.bong@nasa.gov

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IsoGSM-HR (T248, ~50km spatial resolution) [1970~2024, 55 years]

  1. NetCDF_IsotopeVariables
    (https://isotope.iis.u-tokyo.ac.jp/~hayoung/DATAPUB/2025_IsoGSM.ERA5/NetCDF_IsotopeVariables/IsoGSM-HR.T248) 
  2. NetCDF_AllVariables_Monthly
    (https://isotope.iis.u-tokyo.ac.jp/~hayoung/DATAPUB/2025_IsoGSM.ERA5/NetCDF_AllVariables_Monthly/IsoGSM-HR.T248 [tar.gz])
  3. CSV (Surface variables, 6-hourly [2000~2024] & monthly [1970~2024], complementary to the NetCDF data)
    (https://isotope.iis.u-tokyo.ac.jp/~hayoung/DATAPUB/2025_IsoGSM.ERA5/CSV/IsoGSM-HR.T248 [tar.gz])

IsoGSM-LR (T62, ~200km spatial resolution) [1940~2024, 85 years]

  1. NetCDF_IsotopeVariables
    (https://isotope.iis.u-tokyo.ac.jp/~hayoung/DATAPUB/2025_IsoGSM.ERA5/NetCDF_IsotopeVariables/IsoGSM-LR.T62)
  2. NetCDF_AllVariables_Monthly
    (https://isotope.iis.u-tokyo.ac.jp/~hayoung/DATAPUB/2025_IsoGSM.ERA5/NetCDF_AllVariables_Monthly/IsoGSM-LR.T62 [tar.gz]) 
  3. CSV (6-hourly & Monthly, complementary to the NetCDF data)
    (https://isotope.iis.u-tokyo.ac.jp/~hayoung/DATAPUB/2025_IsoGSM.ERA5/CSV/IsoGSM-LR.T62 [ZIP archive containing multiple tar.gz files])

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Format

1. NetCDF_IsotopeVariables

Variables:

1. Precipitation isotopes (mm/day): pratesfc (H₂¹⁶O), prate1sfc (H₂¹⁸O), prate2sfc (HD¹⁶O)
2. 2m (near-surface) specific humidity isotopes (kg/kg): spfh2m (H₂¹⁶O), spfh12m (H₂¹⁸O), spfh22m (HD¹⁶O)

  • Calculation of delta for water isotopes in precipitation:
    • δ¹⁸Oₚ = ((prate1sfc/pratesfc) - 1.)*1000.
    • δDₚ   = ((prate2sfc/pratesfc) - 1.)*1000.
  • Calculation of delta for water isotopes in near-surface vapor:
    • δ¹⁸Oₛ = ((spfh12m/spfh2m) - 1.)*1000.
    • δDₛ   = ((spfh22m/spfh2m) - 1.)*1000.

Value Types and Time Intervals:

Specific humidity isotopes: Instantaneous values recorded at 00, 06, 12, and 18 UTC.
Precipitation isotopes: 6-hour average values corresponding to the following time intervals: 00 UTC (0h < t ≤ 6h), 06 UTC (6h < t ≤ 12h), 12 UTC (12h < t ≤ 18h), and 18 UTC (18h < t ≤ 24h).

Postprocessed Precipitation Isotopes: (Original precipitation isotopes before post-processing contain numerical noise; filtering is required to remove numerical floating-point errors present in small precipitation amounts)

  • Precipitation isotopes (pratesfc, prate1sfc, prate2sfc) are filtered based on the precipitation rate threshold: 0.1 mm/day = 0.00000115740 kg/m²/s (Filtered_0.1mm_per_day), 0.2 mm/day = 0.00000231481 kg/m²/s (Filtered_0.2mm_per_day)
  • A second filtering step is applied based on the δ¹⁸O values that would be calculated from the data, ensuring that only precipitation isotope values (pratesfc, prate1sfc, prate2sfc) that would result in δ¹⁸O values between -100‰ and 10‰ are retained.
  • Filtered grids in NetCDF files are set to FillValue (1.e+20f).

Time Averaging for Daily and Monthly Output

Precipitation isotopes: Computed from either filtered or non-filtered (original) 6-hourly data.
Specific humidity isotopes: Computed from 6-hourly water vapor isotope data.

 

2. NetCDF_AllVariables_Monthly

Variable Information (this monthly output is derived from averaging 6-hourly raw model output. Delta values are calculated from the monthly means of water isotopes (H₂¹⁶O, H₂¹⁸O, HD¹⁶O), rather than from averaged 6-hourly delta values.)

# Variable Long Name Unit
1 d18Op Delta of precipitation per mil
2 dDp Delta of precipitation   per mil
3 dexcessp Delta of precipitation   per mil
4 d18Oe Delta of evaporation per mil
5 dDe Delta of evaporation per mil
6 dexcesse Delta of evaporation per mil
7 d18Os Delta of specific humidity (surface) per mil
8 dDs Delta of specific humidity (surface) per mil
9 dexcesss Delta of specific humidity (surface) per mil
10 d18O Delta of specific humidity (pressure level) per mil
11 dD Delta of specific humidity (pressure level) per mil
12 dexcess Delta of specific humidity (pressure level) per mil
13 d18Ow Delta of vertically integrated water vapor per mil
14 dDw Delta of vertically integrated water vapor per mil
15 dexcessw Delta of vertically integrated water vapor per mil
16 pr Precipitation (surface) mm/day
17 ev Evaporation (surface) mm/day
18 huss Specific humidity (surface) kg/kg
19 hus Specific humidity (pressure level) kg/kg
20 prw Atmospheric column precipitable water kg/m^2
21 tas Temperature (surface) deg C
22 ta Temperature (pressure level) deg C
23 ps Pressure (surface) hPa
24 ua u-wind (pressure level) m/s
25 va v-wind (pressure level) m/s
26 iuq Vertically integrated moisture u-flux kg/m/s
27 ivq Vertically integrated moisture v-flux kg/m/s
28 pref Precipitation efficiency, (pr/prw) * 100 %

(Note: These are Water Isotope Model Intercomparison Project (WisoMIP; Bong et al., 2025, submitted)-type variables for extending model comparisons; see https://portal.nccs.nasa.gov/datashare/giss-publish/pub/paleoclimate/wisomip)

3. CSV (Surface variables, as a complementary format to the NetCDF data)

Grid point-based modeled values, starting from January 1st at 00 UTC, provided in CSV format with the following columns: tmp2m, pr, pr1, pr2, sh, sh1, sh2. Monthly values are calculated by averaging all 6-hourly time steps within each month.

Variables:

tmp2m: 2m temperature (°C)
pr (H₂¹⁶O), pr1 (H₂¹⁸O), pr2 (HD¹⁶O): Precipitation isotopes (mm/day) (raw data, non-filtered data)
sh (H₂¹⁶O), sh1 (H₂¹⁸O), sh2 (HD¹⁶O): Near-surface specific humidity isotopes (kg/kg)
The way to calculate the isotope values (delta): 
  • δ¹⁸Oₚ = ((pr1/pr) - 1.)*1000., δDₚ   = ((pr2/pr) - 1.)*1000.
  • δ¹⁸Oₛ = ((sh1/sh) - 1.)*1000., δDₛ   = ((sh2/sh) - 1.)*1000.

Value Types and Time Intervals:

Temperature (tmp2m) and specific humidity (sh, sh1, sh2): Instantaneous values recorded at 00, 06, 12, and 18 UTC.
Precipitation (pr, pr1, pr2): Average values for 6-hour periods: 00 UTC (0h < t ≤ 6h), 06 UTC (6h < t ≤ 12h), 12 UTC (12h < t ≤ 18h), and 18 UTC (18h < t ≤ 24h).

Usage:

1. Year: Navigate into the directory for the desired year (1940 to 2024)
2. Latitude: Select the latitude directory that is closest to your observation point. The latitude directories are sorted from equatorial to polar regions based on their values.
3. Longitude: Once inside a latitude directory, you will find CSV files named according to longitude. Longitudes are organized from 0° to 360°, covering the full longitudinal range: [0° to 180°E (Eastern Hemisphere) → Represented as 0~180, 180°W to 0° (Western Hemisphere) → Represented as 180~360]

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Alternative link to the datasets, including atmospheric variables:

Directory structure
|
|-- NetCDF_IsotopeVariables
|    |-- IsoGSM-HR.T248 (1970 ~ 2024)
|    |    |-- Surface
|    |    |    |-- Specific_humidity
|    |    |    |    |-- 6-hourly
|    |    |    |    |-- Daily
|    |    |    |    |-- Monthly
|    |    |    |
|    |    |    |-- Precipitation
|    |    |         |-- Original_precipitation
|    |    |         |    |-- 6-hourly  
|    |    |         |    |-- Daily
|    |    |         |    |-- Monthly
|    |    |         |
|    |    |         |-- Filtered_0.1mm_per_day
|    |    |         |    |-- 6-hourly
|    |    |         |    |-- Daily
|    |    |         |    |-- Monthly
|    |    |         |
|    |    |         |-- Filtered_0.2mm_per_day
|    |    |              |-- 6-hourly
|    |    |              |-- Daily
|    |    |              |-- Monthly
|    |    |
|    |    |-- Atmosphere
|    |         |-- Precipitable_water
|    |         |    |-- 6-hourly
|    |         |    |-- Daily
|    |         |    |-- Monthly
|    |         |
|    |         |-- Moisture_flux
|    |              |-- 6-hourly
|    |              |-- Daily
|    |              |-- Monthly
|    |
|    |-- IsoGSM-LR.T62 (1940 ~ 2024)
|         |-- Surface
|         |    |--Specific_humidity
|         |    |    |-- 6-hourly
|         |    |    |-- Daily
|         |    |    |-- Monthly
|         |    |
|         |    |-- Precipitation
|         |         |-- Original_precipitation
|         |         |    |-- 6-hourly  
|         |         |    |-- Daily
|         |         |    |-- Monthly
|         |         |
|         |         |-- Filtered_0.1mm_per_day
|         |         |    |-- 6-hourly
|         |         |    |-- Daily
|         |         |    |-- Monthly
|         |         |
|         |         |-- Filtered_0.2mm_per_day
|         |              |-- 6-hourly
|         |              |-- Daily
|         |              |-- Monthly
|         |
|         |-- Atmosphere
|              |-- Precipitable_water
|              |    |-- 6-hourly
|              |    |-- Daily
|              |    |-- Monthly
|              |
|              |-- Moisture_flux
|                   |-- 6-hourly
|                   |-- Daily
|                   |-- Monthly
|
|-- NetCDF_AllVariables_Monthly (WisoMIP-type variables)
|    |-- IsoGSM-HR.T248 (1970 ~ 2024)
|    |-- IsoGSM-LR.T62 (1940 ~ 2024)
|
|-- CSV (Surface temperature, and isotopes of precipitation and near-surface water vapor)
     |-- IsoGSM-HR.T248
     |    |-- 6-hourly
     |    |    |-- 2000
     |    |    |-- ...
     |    |    |-- 2024
     |    |
     |    |-- Monthly
     |         |-- 1970
     |         |-- ...
     |         |-- 2024
     | 
     |-- IsoGSM-LR.T62
          |-- 6-hourly
          |    |-- 1940
          |    |-- ...
          |    |-- 2024
          |
          |-- Monthly
               |-- 1940
               |-- ...
               |-- 2024

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