AZURE: Auroral Zone Upwelling Release Experiment

The upwelling or vertical circulation that develops in the high-latitude thermosphere is a critical part of the response of the high-latitude thermosphere to auroral forcing. The large vertical gradients in composition and density make it possible for even small vertical flow velocities to produce large changes in the chemistry and dynamics of the region. The vertical flow response is therefore essential to our understanding of the plasma-neutral interactions, energy deposition and redistribution. The limited available measurements, mostly from ground-based Fabry-Perot instruments have consistently shown large vertical winds with magnitudes of 20 to 30 m/s, even in conditions of low to moderate activity. Such large vertical winds typically require large horizontal gradients in the flow to support the circulation, based on the mass continuity equation, but the observed flows also frequently are in the same direction, i.e., either upward or downward, for extended periods of an hour or longer, suggesting that they are large-scale flows rather than narrow features. The combination of the long time scales and large magnitudes makes it difficult to explain the observations. We propose the first set of comprehensive measurements of the vertical winds over the full height range from the lower E region to the F region in the auroral zone during disturbed conditions. Specifically, small lithium cloud releases deployed from rocket-propelled, ejectable canisters will be used as a tracer of the neutral atmospheric motions from which both the horizontal and vertical wind components can be obtained. Specifically, two rockets with apogee near 500 km will be launched from Poker Flat, Alaska, during disturbed conditions near magnetic midnight. Each rocket will carry a total of 12 canister pairs ejected on the upleg. The ejection times and canister detonation sequence will be designed to produce horizontal separations of approximately 50 km between canister pairs and altitude coverage over the range from approximately 110 to 250 km in the general region of the downleg portion of the trajectory. Two-channel photometers on each payload will provide the red and green line altitude profiles. Ionization gauges on each payload will provide neutral density profiles. Time history of the vertical and horizontal winds will be obtained from ground-based Fabry-Perot instruments located at Poker Flat and in the region north of the launch site. The lithium releases require solar illumination for the lithium releases to be visible. Local magnetic midnight occurs near 0230 LT at Poker Flat. In the March time frame suitable twilight conditions can be obtained in the period close to magnetic midnight in the early morning hours when disturbed conditions frequently occur. The proposed experiment will provide the first measurements of the detailed height profiles of the vertical winds across both the E region and F region, as well as the small-scale horizontal variations in both the horizontal and vertical winds. The measurements can thus be used to determine how the vertical flow develops in response to the forcing, how energy, momentum, and atmospheric constituents are transported, and the extent to which the circulation varies horizontally. The research is directly relevant to the strategic goals expressed in the NASA Heliophysics 2009-2030 road map including - RFA H2: Understand changes in the Earths magnetosphere, ionosphere, and upper atmosphere to enable specification, prediction, and mitigation of their effects. In particular, furthering our understanding of the processes responsible for the vertical circulations has significant implications for the accuracy of operational models of both the neutral and ionized components of the atmosphere. The proposed launch scenario has been discussed with the Sounding Rocket Project Office at Wallops and has been deemed to be practical. More »