Figure 2: The 20 hPa monthly and Southern Hemisphere averaged MERRA-2 temperature increments (red dashed), MERRA-2 sum of temperature increments and radiative tendency (red solid), M2-SCREAM temperature increments (blue dashed), and SCREAM sum of temperature increments and radiative tendency (blue solid).

The global temperature at 20 hPa (Fig. 1b) depicts the cooler than average global temperatures associated with the record cold increments during January through June 2022. The January temperatures are approximately one standard deviation below average, the February temperatures continue to cool, while the March through June temperatures are setting new records for cold global temperatures at 20 hPa. Note that the temperature increments can suggest temperatures larger than the temperature departures. For example, in June 2022 the temperature increments are nearly 3 K/month below the mean, while the temperatures for the month are only ~1.25 K below average indicating the importance of the other terms, such as dynamical forcing and radiative transfer, in determining temperature. Nevertheless, these record cold increments are associated with the record low temperatures.

More evidence that the anomalous increments correspond to expected anomalous water vapor is provided by M2-SCREAM temperature tendency fields (Fig. 2). These are shown averaged over the Southern Hemisphere (SH) rather than globally as the global averaged summed temperature tendencies are much smaller. The M2-SCREAM system’s smaller magnitude temperature increments than MERRA-2 (dashed curves) show that M2-SCREAM can respond radiatively to the water vapor anomaly without a strong reliance on the temperature observations. However, when the analysis and radiative tendencies are summed (solid curves), both systems show similar temperature tendencies indicating that the MERRA-2 increments are replacing the additional water vapor portion of the radiative tendency.