Datasets Used in the Data Assimilation Practice

This project contains example datasets that demonstrate data assimilation concepts through ERA5 reanalysis and NCEP comparison data. The datasets (NetCDF) are designed for students to explore reanalysis products and understand data assimilation principles through practical exercises.

General Dataset Overview

The project primarily uses ERA5 reanalysis data across all tasks (1-4), with NCEP/NCAR Reanalysis data added in Task 4 for comparison purposes. These pre-downloaded datasets save time during the practical session, allowing students to focus on data assimilation concepts rather than data retrieval processes.

Task 1: ERA5 500hPa Geopotential Height Data

• Dataset: ERA5 pressure level data (reanalysis-era5-pressure-levels)
• Variable: Geopotential (z) at 500hPa pressure level
• Temporal coverage: Single time point (January 15, 2023, 12:00 UTC)
• Spatial coverage: North Atlantic/UK region [approximately 80°N-30°S, 60°W-20°E]

This dataset demonstrates ERA5's ability to create "maps without gaps" by combining model and observational data through data assimilation.

Task 4: Time Series Data for Observing System Impact Analysis

Task 4 incorporates two datasets to demonstrate how observing system changes affect reanalysis products. The inclusion of both ERA5 and NCEP data allows for comparison between different reanalysis systems, highlighting how each responds to the same observational changes. This demonstrates that modern reanalysis systems like ERA5 use more advanced assimilation techniques to minimize artificial discontinuities compared to older systems.

ERA5 Total Column Water Vapor Data:

• Dataset: ERA5 monthly averaged single-level data
• Variable: Total Column Water Vapor (TCWV)
• Temporal coverage: 1995-2005 monthly data (spanning the ATOVS satellite introduction in 1998)
• Spatial coverage: Southern Ocean (10°S-50°S)
• Significance: Shows subtle changes in mean values and variability patterns after ATOVS satellite introduction

NCEP/NCAR Reanalysis Data:

• Dataset: The monthly and other derived data currently available on-line
• Variable: Precipitable water (pr_wtr) - equivalent to TCWV
• Temporal coverage: 1995-2005 (matching ERA5 period)
• Spatial coverage: Same Southern Ocean region (10°S-50°S)
• Source: Freely available dataset from NOAA Earth System Research Laboratory

The University of New Hampshire (UNH)/Global Runoff Data Centre (GRDC) composite runoff data combines simulated water balance model runoff estimates derived from climate forcing with monitored river discharge. It can be viewed as a data assimilation applied in a water balance model context (conceptually similar to the commonly used 4DDA techniques used in meteorological modeling). Such a data assimilation scheme preserves the spatial specificity of the water balance calculations while constrained by the more accurate discharge measurement. There are 11 data files in this data set and 1 changemap file which shows the differences between the ISLSCP II land/water mask and the original data set.

With the upgraded Land Surface Models (LSMs) and updated forcing data sets, the GLDAS version 2.1 (GLDAS-2.1) production stream serves as a replacement for GLDAS-001. The entire GLDAS-001 collection from January 1979 through March 2020 was decommissioned on June 30, 2020 and removed from the GES DISC system. For more information, please see the IMPORTANT NOTICE document.This data set contains a series of land surface parameters simulated from the Common Land Model (CLM) V2.0 model in the Global Land Data Assimilation System (GLDAS). The data are in 1.0 degree resolution and range from January 1979 to present. The temporal resolution is 3-hourly. This simulation was forced by a combination of NOAA/GDAS atmospheric analysis fields, spatially and temporally disaggregated NOAA Climate Prediction Center Merged Analysis of Precipitation (CMAP) fields, and observation based downward shortwave and longwave radiation fields derived using the method of the Air Force Weather Agency's AGRicultural METeorological modeling system (AGRMET). The simulation was initialized on 1 January 1979 using soil moisture and other state fields from a GLDAS/CLM model climatology for that day of the year. WGRIB or another GRIB reader is required to read the files. The data set applies a user-defined parameter table to indicate the contents and parameter number. The GRIBTAB file shows a list of parameters for this data set, along with their Product Definition Section (PDS) IDs and units.

ERA-40 Global Upper Air Radiosonde Observation Feedback Record Reports include 6 hourly upper air radiosonde observation (RAOB) feedback record reports from RAOBs used in the ECMWF 45-year reanalysis (ERA-40) covering the period from September 1957 to August 2002. RAOBs, from multiple data sources, were assimilated into an ECMWF model and produced ERA-40. Select variables found in the reports include temperature, pressure, height, relative humidity, specific humidity, zonal wind, and meridional wind speed components. Data may be available at mandatory or significant levels from 1000 millibars to 1 millibars. The metadata generated during the ERA-40 quality control data assimilation process were appended to the input observations. The final combination of input observations and feedback metadata are called feedback record reports.