Clear-sky Spectral Kernels

Spectral Radiative Kernels This repository contains longwave **spectral radiative kernels** for **fluxes**, computed under **clear-sky** conditions using **RTTOV v13**. Fluxes are computed using the three-angle Gaussian quadrature approach following the methodology of Clough et al. (2005). --- Perturbed Variables Radiative kernels are computed with respect to perturbations of the following atmospheric and surface variables: - Surface temperature - unit [mW/(m²·cm⁻¹·K) ]- Air temperature - unit [mW/(m²·cm⁻¹ ·K) ]- Water vapor - unit [mW/(m²·cm⁻¹· ppmv) ]- Ozone (O₃) - unit [mW/(m²·cm⁻¹·ppmv) ]- Carbon dioxide (CO₂) - unit [mW/(m²·cm⁻¹ ·ppmv) ]- Nitrous oxide (N₂O) - unit [mW/(m²·cm⁻¹ ·ppmv) ]- Methane (CH₄) - unit [mW/(m²·cm⁻¹. ppmv) ] var_name - ts- temp- wv- ozo- co2- n2o- ch4 Water Vapor Kernels Two water vapor kernels are provided, both describing the same spectral range: 1. **Logarithmic water vapor kernel**, computed with respect to the natural logarithm of the water vapor concentration. 2. **Linear water vapor kernel**, computed with respect to the absolute change in water vapor concentration. Atmospheric kernels are provided on **18 pressure levels**, spanning the atmosphere from **1000 hPa to 1 hPa**. --- Input Atmospheric Profiles The kernels are derived from **ERA5** atmospheric profiles. For each month: - Profiles are selected every **6 hours**.- Five representative days are sampled.- A total of **20 atmospheric states** per month are used.- Spectral kernels are computed for each atmospheric state and then averaged to obtain a monthly mean kernel. The final products are based on **7 years (2008–2014)** of ERA5 data. --- Available Products ## Spectral Flux Kernels Example filename: `{var_name}_jac_spectral_fluxes_kernel_longwave_clear.nc` ## Broadband Kernels (spectral integral of spectral flux kernels) Example filename: `{var_name}_jac_broadband_fluxes_kernel_longwave_clear.nc` Characteristics: - Clear-sky conditions.- Computed using the **three-angle Gaussian quadrature**.- Monthly climatology based on **ERA5 (2008–2014)**. --- Spectral Grid Each kernel file has the following dimensions: - Pressure levels: **18**- Latitude: **90**- Longitude: **144**- Spectral channels: **265** The spectral kernels are computed with a **10 cm⁻¹ spectral sampling**, covering the range from **110 to 2750 cm⁻¹**. This spectral range encompasses the observations of both the **FORUM** and **IASI** instruments. The corresponding **Instrument Spectral Response Functions (SRFs)** are applied during the radiative transfer calculations performed by RTTOV. ---