Ralph Latteck

First common volume observations of layered plasma structures and polar mesospheric summer echoes by rocket and radar

We report the results from simultaneous radar and rocket measurements of a PMSE event where for the first time the rocket measured dust and plasma within the radar beam. We find very clear correspondence between the measured dust charge density profile and the radar backscatter profile as a function of height. We find that even very small amounts of charged dust is associated with an appreciable PMSE radar backscatter. Although we find it likely that the dust layer corresponds fully with the PMSE layer there is a possibility that the upper part of the PMSE layer may be influenced by ion clusters which are too small to be detected by the rocket dust probe.

Temperature and wind tides around the summer mesopause at middle and arctic latitudes

Abstract Temperatures and winds have been determined with a meteor radar at middle and arctic latitudes. Temperatures are estimated as daily averages around 90 km and winds as hourly means between about 82 km and 98 km. Tides are extracted by a superposed epoch analysis using data from periods of typically 10 or 20 days. The variability of meteor radar temperatures and winds obtained at mid-latitudes during summer in 2000 and 2001 as well as at arctic latitudes in summer 2002 is discussed. The observed low temperatures in early summer (150–170K at 54°N and 120–130K at 69°N) are correlated with the appearance of strong mesospheric radar echoes in the VHF range and of noctilucent clouds at arctic latitudes. At mid-latitudes the amplitudes of the diurnal and semidiurnal temperature tide are in the order of 5 K during summer. The tidal amplitudes at arctic latitudes are smaller with about 4 K for the diurnal tide and 2 K for the semidiurnal tide. The steep temperature decrease from spring to summer at mid-latitudes is accompanied by an enhanced semi-diurnal temperature tide (7–10 K) between middle of May and middle of June.

Gravity wave momentum fluxes from MF and meteor radar measurements in the polar MLT region

Annual cycles of horizontal winds and gravity wave (GW) momentum fluxes in the mesosphere/ lower thermosphere (MLT) are presented for the medium frequency Doppler radar at Saura (SMF radar, located at 69◦N, 16◦E) for the first time. Four year mean wind and momentum flux fields for 2008 through 2011 clearly show the coupling and interactions between GWs and the mean flow especially in the summer months. GW breaking at mesopause heights results in momentum flux divergence and affects the wind field by forcing a reversal of the wind profile in summer. Height-time cross sections for the individual years (2008 to 2011) illustrate the year-to-year variation of horizontal winds and the vertical fluxes of zonal and meridional momentum. They show similar annual patterns from year to year which are more consistent in the summer months than during winter and have maximum absolute values in 2009. Furthermore, the precise SMF radar measurements give an excellent possibility to evaluate momentum flux estimates from the colocated meteor radar at Andenes. Both radars have different capabilities, and different techniques are applied to derive momentum fluxes. They show comparable results for the 4 year mean annual cycles of horizontal winds and momentum fluxes especially in summer. This holds for both structure and magnitudes in the overlapping heights, where the SMF radar data provide a wider vertical coverage. The best agreement is found for the zonal components of both radars, whereas there are some larger discrepancies in the meridional components, especially in the vertical flux of meridional momentum.

Mesosphere summer echoes as observed by VHF radar at Kühlungsborn (54°N)

We give a summary report on the properties of Mesosphere Summer Echoes (MSE) layers as observed throughout a complete summer season. The observations were performed with the new 53.5 MHz radar system at Kuhlungsborn (54.1°N, 11.8°E) during the summer 1998. MSE are the equivalent of Polar Mesosphere Summer Echoes (PMSE) at midlatitudes. MSE events have been observed only during day-time, even though the radar was operated continuously. MSE were observed on 34 days for a total of 92 hours and only during sunlit conditions. The first and last MSE events of the season have been detected on June 2 and on August 3, 1998, respectively. Most of the MSE events have had a duration of the order of one to five hours. Two long lasting events have been observed on June 13 and 26 with a duration of 8 and 12 hours. On both dates, noctilucent cloud (NLC) layers were present and colocated lidars observed NLC overhead at night on June 13.

Rocket probe observations of electric field irregularities in the polar summer mesosphere

Electric field wave measurements gathered on a sounding rocket flown in the presence of polar mesospheric summer echoes reveal a distinct layer of irregularities between 83 - 86 km with broadband amplitudes of > 10 mV/m rms. The waves are characterized by bursty, spiky waveforms with lower frequencies (∼ 10 Hz) dominant in the upper portion of the layer near 85 km and broader band emissions, extending to higher frequencies (∼ 1000 Hz) dominant in the lower portion of the layer near 83.5 km. The lower altitudes correspond to a region of weak optical emissions associated with a noctilucent cloud. The waves appear in and around regions where charged/neutral aerosols (1 - 10 nm) and large electron density depletions were observed. The irregularities likely result from a variety of processes including space charge inhomogeneities, mixed neutral and plasma motions, and complex effects associated with charged aerosols of varying sizes.

Rocket probing of PMSE and NLC — Results from the recent MIDAS/MaCWAVE campaign

Abstract From 29 June to 6 July 2002, the European/American MIDAS/MaCWAVE campaign took place at the Andoya Rocket Range (69°N, 16°E) in Norway. Three MMAS payloads were launched in two different salvoes to study the thermal and dynamical environment of Polar Mesosphere Summer Echoes (PMSE) and noctilucent clouds (NLC). All the payloads were equipped with instruments to measure the number density of positive ions, electrons, charged aerosol particles, and neutrals. An electric field experiment was also included aboard one of the MIDAS payloads. An overview of the preliminary results from the campaign will be presented with emphasis on the first salvo where both NLC and PMSE were present. In particular, the small-scale structures measured during passage through these layers will be compared to previous measurements performed in NLC and PMSE conditions.

Dependence of polar mesosphere summer echoes on solar and geomagnetic activity

Abstract Observations of polar mesosphere summer echoes (PMSE) were carried out at Andenes (69.3°N, 16.0°E) with the ALOMAR SOUSY radar during 1994–1997 and with the ALWIN radar during 1999. These data have been used to investigate the dependence of PMSE on solar and geomagnetic activity. Mainly during night-time and the morning hours a significant correlation was found between the signal-to-noise ratio (SNR) of the radar echoes and the geomagnetic K indices of Tromso (69.66°N, 18.94°E). This correlation is markedly smaller during afternoon. Supported by investigations with riometer observations at Andenes and Ivalo (68.55°N, 27.28°E) the diurnal variation of the correlation between SNR and geomagnetic activity can be explained by the diurnal variation of ionization due to precipitation of high energetic particles. Changes of the solar wave radiation characterized by the Lyman α radiation or the solar 10.7 cm radio flux (F10.7 index), however, do not create significant PMSE variations.

Extended observations of polar mesosphere winter echoes over Andøya (69°N) using MAARSY

Continuous observations of Polar Mesosphere Winter Echoes (PMWE) have been conducted at the Norwegian island Andoya (69.30°N, 16.04°E) since autumn 2004 using the ALWIN VHF radar (until 2008) and the Middle Atmosphere Alomar Radar System (MAARSY) (since 2011). Using the more sensitive MAARSY compared to the ALWIN radar results in more detections characterized by smaller volume reflectivity values down to 4·10−18m−1 and a greater altitudinal coverage, 50–88 km compared to previous observations between 65 and 75 km. The results obtained by MAARSY show that the PMWE season starts clearly at the beginning of September with a mean seasonal occurrence rate of about 16%, but a strong seasonal variability with maxima up to 70% in the seasonal variation of the individual years. The end of the winter season is hard to determine since mesospheric echoes have also been observed below altitudes of 80km during nonwinter months, particularly around the end of May, i.e., the beginning of the polar mesospheric summer echo season, indicating that the physical mechanism for creating the lower mesospheric echoes is present during the early summer months as well.

Winter/summer transition in the Antarctic mesopause region

A new set of temperature data with unprecedented resolution and accuracy has been obtained from Fe lidar measurements at Davis, Antarctica (69∘S). Here we concentrate on the months of the winter/summer transition (November to February) where we have collected a total of 1305 hours of observations in the three seasons 2010/2011, 2011/2012, and 2012/2013. The temporal development of temperatures around the mesopause in 2012/2013 is rather similar to the northern hemisphere (NH), whereas the other seasons are significantly different, exhibiting, e.g., an unusual higher and colder mesopause around solstice (‘elevated summer mesopause’, ESM). During this exceptional period mean daily mesopause heights and temperatures are approximately 92.0±0.5 km and 125 K, respectively. The seasonal variation of temperatures in the mesopause region is closely related to the circulation in the stratosphere which exhibits an early (late) vortex breakdown in 2012/2013 (2010/2011). The situation is more complicated in 2011/2012. The early (late) transition in the mesopause region is accompanied by an early (late) appearance of polar mesosphere summer echoes (PMSE). Zonal winds as measured by an MF radar also show systematic differences with westward winds reaching up to very high altitudes (nearly 100 km) for the late transition in 2010/2011 and to more common heights (∼90km) for the early transition in 2012/2013. A mesopause being higher and colder compared to the NH (as occasionally observed at Davis) cannot be achieved by standard models. More sophisticated characterization of gravity wave forcing might be required.

Multi-beam radar observations of polar mesosphere summer echoes during the MIDAS/DROPPS/MiniDUSTY campaign at Andenes, Norway in July 1999

Abstract The dynamical and physical parameters of polar mesosphere summer echoes (PMSE) and noctilucent clouds (NLC) have been studied using co-ordinated rocket, radar, and lidar experiments (ALWIN MST radar, ALOMAR MF radar, and ALOMAR RMR lidar) at Andenes, Norway during the MIDAS/DROPPS/Mini-DUSTY campaign. A strong, long lasting PMSE event connected with a weak NLC was present during the first salvo on July 5/6, 1999. The ALWIN MST radar (53.5 MHz) performed spaced antenna measurements and Doppler beam steering observations using nine beam directions (vertical beam and oblique beams at 7° and 14° off-zenith). For the first time radar observations were possible along rocket trajectories allowing common-volume observations on intersections at altitudes between 75 and 90 km. The observed PMSE characteristics (echo power, aspect sensitivity, spatial coherence, wind field) are discussed with particular emphasis to the times of rocket soundings.