Abstract. The newly-installed MFR (medium frequencyradarAnnual climatologies involving both height and frequency versus time contour plots for periods from 8 h to 30 days, show that the changes with longitude are very significant and distinctive, often exceeding the local latitudinal variations. Comparisons with models and the recent UARS-HRDI global analysis of tides are discussed. The fits of the horizontal wave numbers of the longer period oscillations are provided in unique frequency versus time contour plots and shown to be consistent with the expected dominant modes. Annual climatologies of planetary waves (16 day, 2 day) and gravity waves reveal strong seasonal and longitudinal variations.

[1] The newly installed medium frequency radar (MFR) at Platteville provides unique opportunities to assess latitudinal effects in both the ionosphere and mesosphere-lower thermosphere (MLT) by comparisons with the long-established MFR at Saskatoon. The influence of the D region ''winter anomaly'' is evident in both ionospheres, and descending ''sporadic layers'' (110-90 km) are identified, especially at 40°N, for the first time for MF radar systems. Preliminary comparisons with the wind measurements are made, and the processes are identified as complex. Contour plots of mean winds, tides (12-and 24-hour), and planetary waves (PW) (2-and 16-day) demonstrate significant trends over 12°of latitude (1100 km). The 24-hour tide dominates at 40°N, the 12-hour tide dominates at 52°N, and PW structures demonstrate spatial and temporal intermittency. The two radars are now part of a new network, Canada U.S. Japan Opportunity (CUJO), stretching from 81°W to 141°E.

In this paper, analysis of wind data detected by six ground‐based radar systems located in equatorial and midlatitude belts shows that a strong mesospheric 6.5‐day wave event occurred during April–May 2003. We compared the global distribution of the observed 6.5‐day wave event with the theoretical wave structure (Rossby normal mode (s, n) = (1, −2)). Additionally, we investigated several important wave characteristics to understand the mesospheric 6.5‐day wave event, i.e., wave period, vertical structure, relationship with background wind, propagating direction, and the zonal wave number. Our results are summarized into three points: (1) the latitudinal structure of the mesospheric 6.5‐day wave during April–May 2003 is basically in agreement with the theoretical Rossby mode (s, n) = (1, −2), although the wave amplitude of zonal wind peaked at the subequatorial latitude of Northern Hemisphere but not at the theoretical place, equatorial region; (2) the main wave periods and the altitude distribution of large amplitude of this wave event varied with latitude; (3) the downward propagating wave phases indicated that this wave event originated in the lower atmosphere and propagated upward to the upper region.

Abstract. New techniques are applied to measured Doppler velocity and angle of arrival to estimate horizontal wind vectors, variances, and momentum fluxes, from MF radar data. The approach used to estimate mean winds was first introduced as "time domain interferometry" (TDI) by Vandepeer and Reid [1995]. In the present paper, the algorithm is refined and used with data from the Urbana MF radar, which employs a single vertical antenna beam, to obtain a monthly mean wind climatology which is compared with the results from conventional spaced antenna full correlation analysis. The comparison validates the scattering model used in the development of the TDI technique and highlights instrumental and processing biases that differ between the two techniques. An extension of the TDI method that can provide estimates of the Reynolds stress tensor associated with propagating gravity waves is also proposed, and some preliminary results are presented.

A summary of the first 18 months of continuous wind observations using the Urbana medium frequency (MF) radar is presented. Emphasis is placed on height-time contours of monthly mean winds and on amplitudes and phases of 24 hour and 12 hour tides. Results are compared with data from other midlatitude stations and models. Below 85 kin, monthly mean winds are shown to agree closely with the zonal mean, geostrophic wind model CIRA86. Significant dis•ancies above 85 km have been noted in comparisons between CIRA86 and the other mesosphere-!ower-thermosphere (MLT) radar stations (including MF, meteor, and low-frequency (IF)refers)and are also sustained in the observations reported here. Tidal characteristics are generally consistent with other midlatitude observations, although significant differences are noted between Urbana and its closest MLT network neighbor station (Durham, 43øN, 71øW). The mean wind observations provide a context for the gravity wave climatology derived from Na lidar observations at Urbana and promise to contribute toward improvements of middle atmosphere wind and tidal models. INTRODUCTIONThe past 20 years have been characterized by rapid improvements in the quantity and quality of observational data pertaining to mean winds and tides in the middle atmosphere.A variety of radar techniques have contributed measurements of winds in the 60 to 100 km altitude region, and a few stations have been collecting such data for a number of years. Under the auspices of the Middle Atmosphere Program (MAP), techniques used for the extraction of information from winds measured by radar techniques were improved and standardized.These studies showed that continuous measurements in both height and time are extremely useful for studying the longperiod oscillations in the middle atmosphere. The MAP studies revealed a need for a more complete global network of radars that can provide temporally continuous wind data. Manson et al. [1985aManson et al. [ , 1990Manson et al. [ , 1991 have compiled a detailed comparison of the mean winds obtained from midlatitude radar observations, and Manson et el. [1991] report detailed comparisons between observations and CLRA1986. In another study, Manson et el. [1989] summarized and compared semidiurnal and diurnal tidal climatologies derived from radar measurements at middle latitudes. The radar climatologies were also compared with the most current tidal models. In this paper we concentrate on descriptive analysis of the monthly mean winds and tidal parameters at Urbana and also compare and contrast the observations with those reported by other midlatitude stations. The mean wind and tidal climatology data presented here are intended to complement those presented by Manson et at. [1989, I991] and add one more midlatitude data point to the developing picture of midlatitude mesospheric dynamics. It is expected that the continuous data set being collected at Urbana, when combined with data collected at other midlatitude stations, will provide much useful information on the Copyfight...

Abstract. Following earlier comparisons using the Canadian Middle Atmosphere Model (CMAM, without interactive chemistry), the dynamical characteristics of the model are assessed with interactive chemistry activated. Timesequences of temperatures and winds at Tromsø (70 • N) show that the model has more frequent and earlier stratospheric winter warmings than typically observed. Wavelets at mesospheric heights (76, 85 km) and from equator to polar regions show that CMAM tides are generally larger, but planetary waves (PW) smaller, than medium frequency (MF) radar-derived values.Tides modelled for eight geographic locations during the four seasons are not strikingly different from the earlier CMAM experiment; although monthly data now allow these detailed seasonal variations (local combinations of migrating and non-migrating components) within the mesosphere (circa 50-80 km) to be demonstrated for the first time. The dominant semi-diurnal tide of middle latitudes is, as in the earlier papers, quite well realized in CMAM. Regarding the diurnal tide, it is shown here and in an earlier study by one of the authors, that the main characteristics of the diurnal tide at low latitudes (where the S (1,1) mode dominates) are well captured by the model. However, in this experiment there are some other unobserved features for the diurnal tide, which are quite similar to those noted in the earlier CMAM experiment: low latitude amplitudes are larger than observed Finally, the seasonal variations of planetary wave (PW) activity available from CMAM and the MFR show quite good agreement, apart from the amplitude differences (smaller in CMAM above 70 km). A major difference for the 16-d PW is that CMAM shows large amplitudes before the winter solstice; and for the 2-d PW, while both CMAM and MFR show summer and winter activity, the observed summer mesopause and winter mesospheric wave activities are stronger and more extended in height.Models such as CMAM, operated without dataassimilation, are now able to provide increasingly realistic climatologies of middle atmosphere tides and PW activity. Differences do exist however, and so discussion of the various factors affecting tidal and PW characteristics in atmospheres, modelled and observed, is provided. Other diagnostics of model-characteristics and of future desirable model experiments are suggested.

Using 5 years of all-sky OH airglow imager data over Yucca Ridge Field Station, CO (40.7°N, 104.9°W), from September 2003 to September 2008, we extract and deduce quasi-monochromatic gravity wave (GW) characteristics in the mesopause region. The intrinsic periods are clustered between approximately 4 and 10 min, and many of them are unstable and evanescent. GW occurrence frequency exhibits a clear semiannual variation with equinoctial minima, which is likely related to the seasonal variation of background wind. The anomalous propagation direction in January 2006, with strong southward before major warming starting in 21 January and weak southward propagation afterward, was most likely affected by stratospheric sudden warming. The momentum fluxes show strongly anticorrelated with the tides, with~180°out of phase in the zonal component. While in the meridional component, the easterly maximum occurred approximately 2-6 h after maximum easterly tidal wind. However, the anticorrelations are both weakest during the summer. The dissipating and breaking of small-scale and high-frequency GW's components could have a potential impact on the general circulation in the mesopause region.

Mesospheric winds from three longitudinal sectors at 65°N and 54°N latitude are combined to diagnose the zonal wave numbers (m) of spectral wave signatures during the Southern Hemisphere sudden stratospheric warming (SSW) 2019. Diagnosed are quasi-10-and 6-day planetary waves (Q10DW and Q6DW, m = 1), solar semidiurnal tides with m = 1, 2, 3 (SW1, SW2, and SW3), lunar semidiurnal tide, and the upper and lower sidebands (USB and LSB, m = 1 and 3) of Q10DW-SW2 nonlinear interactions. We further present 7-year composite analyses to distinguish SSW effects from climatological features. Before (after) the SSW onset, LSB (USB) enhances, accompanied by the enhancing (fading) Q10DW, and a weakening of climatological SW2 maximum. These behaviors are explained in terms of Manley-Rowe relation, that is, the energy goes first from SW2 to Q10DW and LSB, and then from SW2 and Q10DW to USB. Our results illustrate that the interactions can explain most wind variabilities associated with the SSW. Plain Language Summary Sudden stratospheric warming events occur typically over the winter Arctic and are well known for being accompanied by various tides and Rossby waves. A rare SSW occurred in the Southern Hemisphere in September 2019. Here, we combine mesospheric observations from the Northern Hemisphere to study the wave activities before and during the warming event. A dual-station approach is implemented on high-frequency-resolved spectral peaks to diagnose the horizontal scales of the dominant waves. Diagnosed are multiple tidal components, multiple Rossby normal modes, and two secondary waves arising from nonlinear interactions between a tide component and a Rossby wave. Most of these waves do not occur in a climatological sense and occur around the warming onset. Furthermore, the evolution of these waves can be explained using theoretical energy arguments.