Global Satellite Observations of Negative Brightness Temperature Differences between 11 and 6.7 µm

Abstract

Abstract Global analyses of satellite spectral observations indicate the existence of negative brightness temperature differences between 11 and 6.7 µm (BT11 −BT6.7) when cold scenes are viewed. Differences are typically greater than −5 K for the Tropics and midlatitudes but can be smaller than −15 K over high-altitude polar regions during winter. In July, more than 60% of the observations over the Antarctic Plateau had BT11 − BT6.7 < −5 K. In January, over Greenland, the frequency of occurrence is approximately 20%. Three factors are investigated that may contribute to these observed negative brightness temperature differences: 1) calibration errors, 2) nonuniform scenes within the field of view, and 3) physical properties of the observed phenomena. Calibration errors and nonuniform scenes may generate values of BT11 − BT6.7 that are less than zero; however, these differences are on the order of −2 K and, therefore, cannot fully explain the observations. A doubling and adding radiative transfer model is ...