Summary:

## Anomaly Forcing in CLM

The 'Anomaly Forcing' atmospheric forcing mode in the Community Land Model (CLM) provides a way to drive the model with projections of future climate conditions without requiring large, high-frequency datasets. This is achieved by:

1. Obtaining a climate simulation that spans both the historical and future time periods.
2. Creating anomalies by removing a climatological seasonal cycle (based on the end of the historical period) from each year of the future time period.
3. Applying these anomalies to a repeating high-frequency forcing dataset of finite duration (e.g., 10 years).

The adjustments are made as follows:

- For state variables (temperature, pressure, humidity, wind), the adjusted value is the sum of the reference value and the additive anomaly.
- For flux variables (precipitation, shortwave radiation, longwave radiation), the adjusted value is the product of the reference value and the multiplicative anomaly.

This approach allows CLM to be driven by projections of future climate conditions without the need for large, high-frequency datasets.