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The coupling between the neutral and ionized atmosphere is important to improve our understanding of the dynamics of the upper atmosphere and thus improving the prediction of space weather. The Arctic atmosphere is a natural laboratory for understanding these processes. The High-frequency Active Auroral Research Program (HAARP) facility located in Gakona Alaska hosts many scientific instruments that can be used for active experiments. An all-solid state Iron Resonance Temperature Lidar system is under development to be deployed at HAARP to enrich the capability of the HAARP facility. We present recent developments of this lidar system. Progress has been made on the development of the transmitter, and the etalon-based laser frequency monitoring system. We are modifying a commercial Nd:YAG laser to operate at 1116 nm. We have achieved broadband lasing at 1116 nm with 1mJ at 100 Hz in long-pulse mode. The 1116 nm laser will be Q-switched and injection seeded to yield narrowband high power emission. The light will then be tripled to 372 nm and serve as the lidar transmitter. Using a frequency-lock Rb laser, we demonstrate accurate monitoring of the laser’s frequency differences when locked to different Doppler free features with errors <1 MHz. This will support the measurement of temperature with this lidar. 

Abstract Using 17 years of Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) data, significant responses of gravity wave (GW) variances, zonal winds and parameterized GW drag to the Madden‐Julian Oscillation (MJO) are identified globally during boreal winter, and their relations are examined. The relative anomalies of GW variances range from −4% (phase 7) to 8% (phase 4) in tropics, and −20% (phase 1) to 20% (phase 5) in the northern polar region (NPR). The anomalies of zonal winds are from −3–3 m/s and −4–8 m/s in tropics and NPR, respectively. The vertical and latitudinal structures of MJO signals in GW, wind and GW drag show coherent patterns. Further analysis implies that in the NPR, the eastward wind leads to westward momentum flux carried by the GWs. This flux leads to westward drag, which drives that of zonal winds and imprint the MJO signal in GWs to the wind. 

A narrowband sodium resonance wind-temperature lidar (SRWTL) has been deployed at Poker Flat Research Range, Chatanika, Alaska (PFRR, 65° N, 147° W). Based on the Weber narrowband SRWTL, the PFRR SRWTL transmitter was upgraded with a state-of-the-art solid-state tunable diode laser as the seed laser. The PFRR SRWTL currently makes simultaneous measurements in the zenith and 20° off-zenith towards the north with two transmitted beams and two telescopes. Initial results for both nighttime and daytime measurements are presented. We review the performance of the PFRR SRWTL in terms of seven previous and currently operating SRWTLs. The transmitted power from the pulsed dye amplifier (PDA) is comparable with other SRWTL systems (900 mW). However, while the efficiency of the seeding and frequency shifting is comparable to other SRWTLs the efficiency of the pumping is lower. The uncertainties of temperature and wind measurements induced by photon noise at the peak of the layer with a 5 min, 1 km resolution are estimated to be ~1 K and 2 m/s for nighttime conditions, and 10 K and 6 m/s for daytime conditions. The relative efficiency of the zenith receiver is comparable to other SRWTLs (90–97%), while the efficiency of the north off-zenith receiver needs further optimization. An upgrade of the PFRR SRWTL to a full three-beam system with zenith, northward and eastward measurements is in progress. 

Abstract The 17‐year SABER‐observed gravity wave (GW) temperature variances reveal significant responses of GWs to the Madden‐Julian Oscillation (MJO) over the middle atmosphere (30–100 km) in tropics and extratropics (45°S to 45°N) for boreal winter. The responses vary significantly with latitude but barely with altitude. From 20°S to 45°N, strong positive anomalies are found for MJO Phases 3–5, while negative anomalies for Phases 7–8. From 45–20°S, these patterns are reversed. The peak‐to‐peak differences (positive‐to‐negative anomalies) are ~6–16% relative to the seasonal mean. Comparison with MJO modulations on tropical convection and polar vortex suggests that GW responses in tropics may result from the modulation of GW source, while responses in northern extratropics may result from the modulation of polar vortex, which in turn modulates GW activities. These results highlight the importance of GWs to imprint the tropical MJO signals vertically to the middle atmosphere and horizontally to extratropical regions. 

Abstract On the night of 18–19 October 2018, sodium resonance lidar measurements show the presence of overturning in the mesospheric sodium layer. Two independent tracers, sodium mixing ratio and potential temperature, derived from resonance and Rayleigh lidar measurements, reveal that vertical spreading of the sodium mixing ratio contours and a layer of convective instability coincide with this overturning. Analysis of lidar measurements also reveals the presence of gravity waves that propagate upward, are saturated, and dissipate at the height of the convective instability. The vertical spreading is analyzed in terms of turbulent diffusive transport using a model based on material continuity of sodium. Estimates of the turbulent eddy diffusion coefficient, K, and energy dissipation rate,εare derived from the transport model. The energy dissipated by the gravity waves is also calculated and found to be sufficient to generate the turbulence. We consider three other examples of overturning, instability and spreading on the nights of: 17–18 February 2009, 25–26 January 2015, and 8–9 October 2018. For all four events we find that the values of K (∼1,000 m²/s) are larger and the values ofε(∼10–100 mW/kg) are of similar magnitude to those values typically reported by ionization gauge measurements. These examples also reveal that higher levels of turbulent mixing are consistently found in regions of lower stability. 

Abstract Though the Kelvin‐Helmholtz instability (KHI) has been extensively observed in the mesosphere, where breaking gravity waves produce the conditions required for instability, little has been done to describe quantitatively this phenomenon in detail in the mesopause and lower thermosphere, which are associated with the long‐lived shears at the base of this statically stable region. Using trimethylaluminum (TMA) released from two sounding rockets launched on 26 January 2018, from Poker Flat Research Range in Alaska, the KHI was observed in great detail above 100 km. Two sets of rocket measurements, made 30 min apart, show strong winds (predominantly meridional and up to 150 ms⁻¹) and large total shears (90 ms⁻¹ km⁻¹). The geomagnetic activity was low in the hours before the launches, confirming that the enhanced shears that triggered the KHI are not a result of the E‐region auroral jets. The four‐dimensional (three‐dimensional plus time) estimation of KHI billow features resulted in a wavelength, eddy diameter, and vertical length scale of 9.8, 5.2, and 3.8 km, respectively, centered at 102‐km altitude. The vertical and horizontal root‐mean‐square velocities measured 29.2 and 42.5 ms⁻¹, respectively. Although the wind structure persisted, the KHI structure changed significantly with time over the interval separating the two launches, being present only in the first launch. The rapid dispersal of the TMA cloud in the instability region was evidence of enhanced turbulent mixing. The analysis of the Reynolds and Froude numbers (Re = 7.2 × 10³andFr = 0.29, respectively) illustrates the presence of turbulence and weak stratification of the flow.