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.