[1] The Southern Argentina Agile Meteor Radar (SAAMER) was installed at Rio Grande on Tierra del Fuego (53.8°S, 67.8°W) in May 2008 and has been operational for ∼24 months. This paper describes the motivations for the radar design and its placement at the southern tip of South America, its operating modes and capabilities, and observations of the mean winds, planetary waves, and tides during its first ∼20 months of operation. SAAMER was specifically designed to provide very high resolution of large-scale motions and hopefully enable direct measurements of the vertical momentum flux by gravity waves, which have only been possible previously with dual-or multiple-beam radars and lidars or in situ measurements. SAAMER was placed on Tierra del Fuego because it was a region devoid of similar measurements, the latitude was anticipated to provide high sensitivity to an expected large semidiurnal tide, and the region is now recognized to be a "hot spot" of small-scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere, perhaps the most dynamically active location on Earth. SAAMER was also intended to permit simultaneous enhanced meteor studies, including "head echo" and "nonspecular" measurements, which were previously possible only with high-power largeaperture radars. Initial measurements have defined the mean circulation and structure, exhibited planetary waves at various periods, and revealed large semidiurnal tide amplitudes and variability, with maximum amplitudes at higher altitudes often exceeding 60 m s −1 and amplitude modulations at periods from a few to ∼30 days.

An Advanced Mesosphere Temperature Mapper and other instruments at the Arctic LidarObservatory for Middle Atmosphere Research in Norway (69.3°N) and at Logan and Bear Lake Observatory in Utah (42°N) are used to demonstrate a new method for quantifying gravity wave (GW) pseudo-momentum fluxes accompanying spatially and temporally localized GW packets. The method improves on previous airglow techniques by employing direct characterization of the GW temperature perturbations averaged over the OH airglow layer and correlative wind and temperature measurements to define the intrinsic GW properties with high confidence. These methods are applied to two events, each of which involves superpositions of GWs having various scales and character. In each case, small-scale GWs were found to achieve transient, but very large, momentum fluxes with magnitudes varying from~60 to 940 m 2 s À2 , which are~1-2 decades larger than mean values. Quantification of the spatial and temporal variations of GW amplitudes and pseudo-momentum fluxes may also enable assessments of the total pseudo-momentum accompanying individual GW packets and of the potential for secondary GW generation that arises from GW localization. We expect that the use of this method will yield key insights into the statistical forcing of the mesosphere and lower thermosphere by GWs, the importance of infrequent large-amplitude events, and their effects on GW spectral evolution with altitude.

A new generation meteor radar was installed at the Brazilian Antarctic Comandante Ferraz Base (62.1°S) in March 2010. This paper describes the motivations for the radar location, its measurement capabilities, and comparisons of measured mean winds, tides, and gravity wave momentum fluxes from April to June of 2010 and 2011 with those by a similar radar on Tierra del Fuego (53.8°S). Motivations for the radars include the “hotspot” of small‐scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere (MLT) centered over the Drake Passage, the maximum of the semidiurnal tide at these latitudes, and the lack of other MLT wind measurements in this latitude band. Mean winds are seen to be strongly modulated at planetary wave and longer periods and to exhibit strong coherence over the two radars at shorter time scales as well as systematic seasonal variations. The semidiurnal tide contributes most to the large‐scale winds over both radars, with maximum tidal amplitudes during May and maxima at the highest altitudes varying from ∼20 to >70 ms−1. In contrast, the diurnal tide and various planetary waves achieve maximum winds of ∼10 to 20 ms−1. Monthly mean gravity wave momentum fluxes appear to reflect the occurrence of significant sources at lower altitudes, with relatively small zonal fluxes over both radars, but with significant, and opposite, meridional momentum fluxes below ∼85 km. These suggest gravity waves propagating away from the Drake Passage at both sites, and may indicate an important source region accounting in part for this “hotspot.”

[1] Mean winds, semidiurnal and diurnal tides, and trends and long-period oscillations spanning a solar cycle (from early 1999 through June 2010) measured by medium frequency (MF) radars at conjugate Antarctic and Arctic latitudes (Syowa, Antarctica, 69°S, 39.6°E, and Andenes, Norway, 69.3°N, 16°E) are described and compared. Zonal mean winds are stronger and more uniform from year to year over the Antarctic, with a stronger eastward winter jet spanning the range of altitudes presented (70 to 96 km). The summer westward jet is also stronger and maximizes at higher altitudes over the Antarctic than over the Arctic. The eastward winter jet over the Arctic, while generally weaker, exhibits a localized maximum in late winter at ∼2 to 3 year intervals. Meridional mean winds likewise achieve somewhat stronger maxima at higher altitudes over the Antarctic than over the Arctic. Semidiurnal tide amplitudes are typically somewhat larger over the Antarctic and similar in the two components, with maxima at ∼85 km or above and narrow responses that tend to cluster from ∼February to May and ∼September to November over the Antarctic and from ∼December to February and ∼June to September over the Arctic. Zonal diurnal tide amplitudes are quite similar between the sites, with maxima extending from ∼70 to 90 km and slightly stronger over the Antarctic. Meridional diurnal amplitudes display more significant growth with altitude, achieve stronger maxima at the highest altitudes presented, and typically exhibit a single and narrow maximum during December to February over the Antarctic and double maxima from ∼May to September over the Arctic. Also discussed are trends and long-period oscillations over a solar cycle observed in these mean and tidal wind fields.

[1] The TIMED Doppler Interferometer (TIDI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite has been measuring horizontal winds in the mesosphere and lower thermosphere (MLT) since 2002. Because of the high inclination of the TIMED orbit, TIDI measures the horizontal winds from pole to pole every orbit. This paper presents the first assessment of the spatial structure and temporal evolution of the nonmigrating semidiurnal tides over the Arctic determined from the TIDI wind measurements and a comparison of the structure of the nonmigrating semidiurnal tide between the Arctic and Antarctic. The nonmigrating semidiurnal tides were determined as a 60 day average based on the yaw cycles of the spacecraft. The nonmigrating semidiurnal tidal wind field over the Arctic comprises mainly the westward-propagating zonal wave numbers 1 (W1) and 3 (W3) and standing zonal wave number 0 (S0) modes. The W1 mode is the most prominent, maximizing above 90 km poleward of 60°N during the yaw interval ranging from mid-March to mid-May. While this mode exhibits a slight amplitude increase toward the North Pole during this interval, its phase is nearly constant with latitude. The S0 mode is enhanced over two yaw intervals ranging from mid-January to mid-May, but its amplitude decreases toward the North Pole. Compared to the W1 semidiurnal tide over the Antarctic, that over the Arctic is smaller in amplitude, of less extended duration, achieves maximum amplitudes at higher altitudes by ∼10 km, and exhibits a weaker amplitude increase toward the pole. These differences likely result from differences in excitation mechanisms and efficiency and/or in propagation conditions in the two responses for the nonmigrating semidiurnal tides between the Arctic and Antarctic.