A global view of stratospheric gravity wave hotspots located with Atmospheric Infrared Sounder observations

Abstract

[1] The main aim of this study is to find and classify hotspots of stratospheric gravity waves on a global scale. The analysis is based on a 9 year record (2003 to 2011) of radiance measurements by the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite. We detect gravity waves based on 4.3 mm brightness temperature variances. Our method focuses on peak events, i.e., strong gravity wave events for which the local variance considerably exceeds background levels. We estimate the occurrence frequencies of these peak events for different seasons and time of day and use the results to find local maxima or "hotspots." In addition, we use AIRS radiances at 8.1 mm to simultaneously detect convective events, including deep convection in the tropics and mesoscale convective systems at middle latitudes. We classify the gravity wave sources based on seasonal occurrence frequencies for convection, but also by means of time series analyses and topographic data. Our study reproduces well-known hotspots of gravity waves, e.g., the Andes and the Antarctic Peninsula. However, the high horizontal resolution of the AIRS observations also allows us to locate numerous mesoscale hotspots, which are partly unknown or poorly studied so far. Most of these mesoscale hotspots are found near orographic features like mountain ranges, coasts, lakes, deserts, or isolated islands. This study will help to select promising regions and seasons for future case studies of gravity waves.Citation: Hoffmann, L., X. Xue, and M. J. Alexander (2013), A global view of stratospheric gravity wave hotspots located with Atmospheric Infrared Sounder observations,

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

“…The analysis of spatial patterns showed that the wave activity is mostly related to orographic, jet, and storm sources. The observed patterns of wave activity agree well with those reported in other climatological studies of global gravity wave activity using AIRS observations (Gong et al, 2012;Hoffmann et al, 2013Hoffmann et al, , 2014. The observed gravity wave activity is closely correlated with zonal winds at the 30 hPa level, which we attribute to the AIRS observational filter.…”

“…We found standard errors of 29-39 % for November to February for the Northern Hemisphere and 18-21 % for May to October for the Southern Hemisphere. The spatial patterns of gravity wave activity in the lower stratosphere found here agree well with those identified by Gong et al (2012) and Hoffmann et al (2013Hoffmann et al ( , 2014Hoffmann et al ( , 2016a for the mid-and upper stratosphere.…”

“…In the Northern Hemisphere, this includes (from west to east) the Arctic Archipelago, Labrador, Greenland, Iceland, the United Kingdom, the Alps, the Scandinavian Mountains, the Ural Mountains, the Altai Mountains, the Central Siberian Plateau, and the East Siberian Plateau. Gravity wave activity over the Rocky Mountains is largely absent, which is due to relatively low stratospheric background winds over this mountain range (Hoffmann et al, 2013(Hoffmann et al, , 2014. In the Southern Hemisphere, we found increased gravity wave activity in a latitude band around 70-50 • S during the winter months, which is attributed mostly to jet and storm sources (Sato et al, 2012;Hendricks et al, 2014;Hindley et al, 2015).…”

“…Robertson Land. Previous climatological studies using AIRS data showed that these regions are in fact hot spots of stratospheric gravity wave activity (Gong et al, 2012;Hoffmann et al, 2013Hoffmann et al, , 2016a. AIRS measurements in the spectral window region at 8.1 µm can be used to detect storm systems Hoffmann and Alexander, 2010).…”

“…For this study, we identified a set of 21 AIRS channels in the 15 µm CO 2 waveband to study gravity wave activity in the polar lower stratosphere. Our channel selection differs from the earlier work of Hoffmann et al (2013Hoffmann et al ( , 2014, which used AIRS channels in the 4.3 µm CO 2 waveband to obtain gravity wave information for the mid-and upper stratosphere. The channels selected for this study are listed in Table 1 together with centroid frequencies and noise estimates (referred to as noise equivalent delta temperature; NeDT) at a 250 K scene temperature.…”