Modis Observations of Deep Convective Cloud Tops

Past studies of the NOAA AVHRR/2 and GOES I-M imagery (e.g., Setvák et al., 1996) have shown that frozen tops of deep convective storms occasionally exhibit significant increase of cloud top reflectivity when observed in the 3.7 or 3.9 μm spectral bands. Similar storm top features have been documented in the NOAA-KLM AVHRR/3 1.6 μm spectral band (Setvák et al., 2003). Consequently, cross-comparison of storm top features observed simultaneously in the NOAA-KLM AVHRR/3 1.6 μm imagery and in the GOES I-M 3.9 μm imagery has shown similar patterns in these spectral bands (Setvák et al., 2003). The present work focuses on storm top observations utilizing the MODIS instrument. The older Terra satellite operates in a late morning orbit (descending node 10:30 a.m.), when deep convection over land is typically at a minimum. Thus, this study utilizes namely data from the Aqua satellite, which has an early afternoon overpass (ascending node 1:30 p.m.), when conditions are more favorable for deep convective development. The main goal of this work is to examine the spectral characteristics of enhanced reflectivity features observed on or above thunderstorm anvils using the multiple visible and infrared bands of MODIS. An additional goal is to improve understanding of moisture entrainment into the stratosphere. For this, we examine the differences in brightness temperature between window and water vapor absorption bands to estimate water vapor above and surrounding deep convective cloud elements which penetrate into the stratosphere (e.g. Schmetz et al., 1997). For both of the previously mentioned topics, the present work targets storms that exhibit plumes above anvil tops (Setvák and Doswell, 1991; Levizzani and Setvák, 1996). The latest observations of plumes from MODIS suggest a new possible interpretation of the “cold-U/V” features, observed occasionally at storm tops (e.g., McCann, 1983).