Quasi 2-day Wave Research Articles

Mean winds, tides, and quasi-2 day waves above Bear Island

A new meteor radar on Bear Island (74.5°N, 19.0°E) has been conducting horizontal wind observations on a regular basis since completion of its installation on 1 November 2007. We have analyzed wind data obtained with the meteor radar between 80 and 100km over 42 months from November 2007 to April 2011, and presented seasonal variations as well as year-to-year variations in mean winds, diurnal and semidiurnal tides based on 1-month averaged wind data. We also presented seasonal variations in quasi-2 day wave (Q2DW). Obtained results are compared with those from Tromsø (69.6°N, 19.2°E) MF radar for the same interval. There is a good agreement in the mean zonal wind, meridional diurnal tide, and semidiurnal tides. In particular, the agreement is excellent for the semidiurnal tides, suggesting the same mode is dominant between 70° and 75° between 82 and 91km in the northern Scandinavia sector. Seasonal variations in the Q2DW at both sites are similar, but the intervals of intermittent activity were not correlated well at the two sites except for the meridional component in summer. In general, the results obtained at Bear Island agree with published results at other high latitude stations in the northern hemisphere. We also showed variations in the mean winds and the semidiurnal tide during the January 2009 Sudden Stratospheric Warming event.

A simulation of the quasi-two-day wave and its effect on variability of summertime mesopause temperatures

The quasi 2-day wave is studied using a multi-year simulation of the Canadian Middle Atmosphere Model. The general characteristics of the wave are presented, and interannual and inter-hemispheric differences are discussed. The simulated quasi 2-day wave amplifies shortly after solstice in the summer hemisphere. The wave exhibits a variable phase speed over the summer season, which decreases as the mesospheric jet weakens. As such, the period is initially shorter than 2 days, but can lengthen to more than 2 days. A 2-day wave index is defined using empirical orthogonal functions, and is used to describe the behaviour of the quasi 2-day wave. The 2-day index is also used to examine the effect of the 2-day wave on mesospheric temperatures through its impact on the residual circulation. It is determined that up to 10% of the interannual variability in the seasonal polar summer mesopause temperatures can be attributed to the simulated quasi 2-day wave. It could, therefore, be a significant source of variability for polar mesospheric clouds.

Dominant winter-time mesospheric wave signatures over a low latitude station, Hawaii (20.8°N): An investigation

We utilize mesospheric O2 airglow emission intensity and temperature data collected during January–February 2003 on 17 consecutive nights from Maui, Hawaii (20.8°N, 156.2°W) to study the dominant and long period wave features at mesospheric altitudes. Apart from large day-to-day variability, it is found that nocturnal data for the period under consideration was dominated by a terdiurnal tide-like wave. Together, a quasi 5-day wave is also noticed with significant amplitude.

High-altitude data assimilation system experiments for the northern summer mesosphere season of 2007

A global numerical weather prediction system is extended to the mesosphere and lower thermosphere (MLT) and used to assimilate high-altitude satellite measurements of temperature, water vapor and ozone from MLS and SABER during May–July 2007. Assimilated temperature and humidity from 100 to 0.001 hPa show minimal biases compared to satellite data and existing analysis fields. Saturation ratios derived diagnostically from these assimilated temperature and water vapor fields at PMC altitudes and latitudes compare well with seasonal variations in PMC frequency measured from the aeronomy of ice in the mesosphere (AIM) satellite. Synoptic maps of these diagnostic saturation ratios correlate geographically with three independent transient mesospheric cloud events observed at midlatitudes by SHIMMER on STPSat-1 and by ground observers during June 2007. Assimilated temperatures and winds reveal broadly realistic amplitudes of the quasi 5-day wave and migrating tides as a function of latitude and height. For example, analyzed winds capture the dominant semidiurnal MLT wind patterns at 55°N in June 2007 measured independently by a meteor radar. The 5-day wave and migrating diurnal tide also modulate water vapor mixing ratios in the polar summer MLT. Possible origins of this variability are discussed.

Springtime effects in the mesosphere and ionosphere observed at northern midlatitudes

Nighttime volume emission rates and rotational temperatures, obtained from simultaneous observations of molecular oxygen and hydroxyl airglow at Almaty (43.25°N, 76.92°E) and Sierra-Nevada (37.2°N, 356.7°E), along with ionospheric density derived from foF2 in the vertical sounding ionograms over Almaty are analysed to study the variability and coupling of parameters observed in the upper mesosphere and ionosphere during the period of February – April, 2000. Ionospheric critical frequency measurements and airglow observations by the Mesopause Rotational Temperature Imager (MORTI) at Almaty and the Spectral Airglow Temperature Imager (SATI) at Sierra-Nevada Observatories show an increase in long-period planetary wave (PW) activity from the end of February until the middle of March, 2000. Very good agreement was found in the temporal variations of emission rates and rotational temperatures from March 1–15, 2000 measured at the Almaty and Sierra-Nevada sites. Similar perturbations could also be seen in the ionospheric critical frequency (ΔfoF2) obtained as a difference between current foF2 values and an ionospheric background level. The perturbations observed have been interpreted employing the Met office stratospheric model results. Latitudinal structure of a quasi 5-day wave was identified, for which the first-symmetric-mode amplitude and symmetric behaviour of phase are in good agreement with theoretical prediction. The analysis of the Met office stratospheric data indicate the presence of westward-propagating PW with periods of ∼5 and 10 days during the period of interest. The temporal correlation between planetary scale oscillations observed in the datasets examined (ionospheric, optical and meteorological) suggest dynamical coupling with the stratosphere. A negative disturbance in ΔfoF2 of ∼25% observed 1 day before a sharp increase in the MORTI mesospheric rotational temperature registered on March 10 at Almaty, is also discussed in the context of the possible stratosphere/mesosphere/ionosphere coupling.

Planetary wave trends in the lower thermosphere—Evidence for 22-year solar modulation of the quasi 5-day wave

Geomagnetic data from five northern hemisphere observatories at latitudes ranging from 22°N to 67°N have been used to investigate long-term trends in planetary wave activity in the lower thermosphere. The data extends back over eight 11-year solar cycles. At quasi 10- and 16-day periods, there is no long-term change in planetary wave activity through the 20th century; decadal-scale variability reaching 25% peak-to-peak is observed. At the quasi 5-day period there is a steady decrease in activity totalling 15% through the 20th century. Additionally, there is a Hale ‘22-year’ solar cycle modulation of ∼20% peak-to-peak in the 5-day planetary wave activity at 22°N which decreases in amplitude with increasing latitude. It is not clear what causative mechanism is responsible for this modulation which shows signs of breaking down at the very end of the century.

Mean winds, tides, and quasi‐2 day wave in the polar lower thermosphere observed in European Incoherent Scatter (EISCAT) 8 day run data in November 2003

Simultaneous European Incoherent Scatter (EISCAT) radar observations using two EISCAT radars, the Tromsø (69.6°N, 19.2°E) UHF radar and the EISCAT Svalbard radar (Longyearbyen, 78.2°N, 16.0°E), were conducted for 8 consecutive days, from 11 to 19 November 2003, to study the lower thermospheric wind dynamics in the polar region. Altitude profiles of the amplitudes of the diurnal and semidiurnal components at Tromsø and Longyearbyen are similar. The semidiurnal amplitudes in the meridional and zonal components exhibit maxima at 105–107 km, with values of ∼70–90 m s−1. The semidiurnal phases vary with roughly a 30 km vertical wavelength between 98 and 110 km. The quasi‐2 day wave (Q2DW) was not detected in the lower thermosphere at either Tromsø or Longyearbyen during the period, while it was found between 70 and 82 km in the mesosphere with the colocated Tromsø MF radar. This observational result suggests that in general, the Q2DW attenuates in the mesosphere and cannot penetrate into the lower thermosphere in winter. Ion drag acceleration of the wind is generally negligible below 107 km at Tromsø and below 118 km at Longyearbyen, but significant ion drag acceleration is found above these heights. A comparison of mean wind and tidal amplitudes and phases with National Center for Atmospheric Research Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics General Circulation Model predictions for the period shows some agreement.

The quasi 2‐day wave observed in the polar mesosphere: Comparison of the characteristics observed at Tromsø and Poker Flat

A comparison of the quasi 2‐day wave (Q2DW) observed at Tromsø (69.6°N, 19.2°E) and Poker Flat (65.2°, 147.6°W) is presented at four heights of 70, 76, 82, and 88 km using wind data taken for ∼4 years, from 1 November 1998 to 7 November 2002. The characteristics of the Q2DW such as seasonal variation, occurrence of period of maximum amplitude, ratio of meridional to zonal amplitudes, shape of altitude profile of phase, and modulation of amplitude at a 4–10 days rate found at Poker Flat are very similar to those found at Tromsø reported by Nozawa et al. [2003]. The activity of the Q2DW is higher in winter than in summer for meridional and zonal components at the two sites. Long‐term variation (i.e., seasonal variation) of the Q2DW is found to be similar between the two sites, while short‐term variations (i.e., over several days) do not synchronize well with each other. The ratio of amplitudes of the Q2DW between the two sites varies mainly between 0.5 and 2, and there is no significant preference toward either site. Phase differences of Q2DWs between the two sites are examined, and it is found that in‐phase‐like events are more frequently seen than out‐of‐phase‐like events at 76, 82, and 88 km in winter and at 88 km in summer. This can be interpreted to mean that the zonal wave number of the Q2DW appears to be 2 or 4 more often than 3 in the polar upper mesosphere. These results suggest that observed Q2DWs have features consistent with the Rossby gravity wave mode, but the amplitude and phase of the Q2DW are affected significantly by local sources. A possibility that the observed Q2DW is an eastward moving wave is also discussed.

High-Frequency Planetary Waves in the Polar Middle Atmosphere as Seen in a Data Assimilation System

This study examines the winter southern hemisphere vortex of 1998 using four times daily output from a data assimilation system to focus on the polar 2-day, wave number 2 component of the 4-day wave. The data assimilation system products are from a test version of the finite volume data assimilation system (fvDAS) being developed at Goddard Space Flight Center (GSFC) and include an ozone assimilation system. Results show that the polar 2-day wave dominates during July 1998 at 70 degrees. The period of the quasi 2-day wave is somewhat shorter than 2 days (about 1.7 days) during July 1998 with an average perturbation temperature amplitude for the month of over 2.5 K. The 2-day wave propagates more slowly than the zonal mean zonal wind, consistent with Rossby wave theory, and has EP flux divergence regions associated with regions of negative horizontal potential vorticity gradients, as expected from linear instability theory. Results for the assimilation-produced ozone mixing ratio show that the 2-day wave represents a major source of ozone variation in this region. The ozone wave in the assimilation system is in good agreement with the wave seen in the POAM (Polar Ozone and Aerosol Measurement) ozone observations for the same time period. Some differences with linear instability theory are noted as well as spectral peaks in the ozone field, not seen in the temperature field, that may be a consequence of advection.

The quasi 2‐day wave observed in the polar mesosphere

Using MF radar data obtained at Tromsø (69.6°N, 19.2°E) for ∼37 months between 1 November 1998 and 8 December 2001, we have examined characteristics of the quasi 2‐day wave (Q2DW) in the polar mesosphere in the height range from 70 to 91 km. The activity of the Q2DW is higher in winter months (November–February) than in summer months (May–August) over this height region. The maximum values of the amplitude are ∼25 m s−1 in winter and ∼15 m s−1 in summer. Between 70 and 82 km, the amplitude appears to maximize near winter solstice over the 3 years. The average ratio of meridional to zonal amplitudes is ∼1.1–1.2 over the height region. Thus, there is no significant preference towards either components. The variations of the periods of maximum amplitude are also examined, and periods with 45.2 and 54.9 hours occur more frequently than those with 48.0 and 51.2 hours. However, no clear seasonal trend of the variation of the period is found. In addition, the amplitude is modulated at 4–10 day rate. With simultaneous observational data from the MF radar and the EISCAT UHF radar colocated in Tromsø, we have examined whether or not the Q2DW was able to penetrate to the lower thermosphere for the period of 1–9 July 1999. It is found that the amplitude of the Q2DW with period of 51.2 hours maximized at 95 km height with values of ∼25 m s−1 in both meridional and zonal components. The Q2DW was attenuated above 95 km, but it appears to survive up to 108 km height in the meridional component. Between 85 and 95 km for the meridional component during this 8‐day interval, the Q2DW and semidiurnal tide were the strongest among the periodic components.

The Seasonal Variation of the Propagating Diurnal Tide in the Mesosphere and Lower Thermosphere. Part I: The Role of Gravity Waves and Planetary Waves

Abstract The seasonal variation of the propagating diurnal tide in the mesosphere and lower thermosphere is examined using results from a 2-yr simulation of the extended version of the Canadian Middle Atmosphere Model (CMAM). The CMAM is shown to be able to reproduce not only the observed semiannual amplitude variation of the tide in the lower thermosphere but also more subtle features such as amplitude maxima that are stronger in March/April than in September/October, a 4- to 6-h shift in phase between winter and summer in the Northern Hemisphere, and a weaker seasonal variation of phase in the Southern Hemisphere. Part I of this two-part series of papers investigates the importance of two of the mechanisms that have been proposed to explain the observed variation of tidal amplitude, namely, 1) interactions with small-scale gravity waves and 2) interactions with planetary-scale waves like the quasi–2-day wave. Analysis of the tidal momentum and thermodynamic budgets shows that the direct effects of param...

Mesosphere/lower thermosphere wind measurements over Europe in summer 1998

In July and August 1998, co-ordinated measurements of winds in the mesosphere/lower thermosphere region were carried out using meteor radars at Obninsk (Russia), Kharkov (Ukraine), Shrivenham (UK), and the low-frequency windprofiler at Collm (Germany). The strongest feature observed during this campaign was a quasi 2-day wave that appeared in the second half of July. This wave had nearly constant phase when a period of 48 h was assumed. Phase comparison between the sites revealed a zonal wave number of 4. The quasi 2-day wave event was connected with a decrease in the zonal prevailing wind, indicating wave-mean flow interaction. In addition, non-linear interaction between the quasi 2-day wave and the semidiurnal tide occurred. In August the quasi 2-day wave amplitude decreased, but other oscillations were still present. A long-period modulation of the semidiurnal tide over Europe was also observed, indicating interaction between the semidiurnal tide and a planetary wave.

Longitudinal variations in planetary wave activity in the equatorial mesosphere

Zonal and meridional winds in the equatorial mesosphere and lower thermosphere (65–98 km) measured at two sites separated by 94° in longitude are used to study the zonal structure of planetary-scale waves. The data were obtained with MF radars located at Pontianak (0°N, 109°E)and Christmas Island (2°N, 157°W). The data at Christmas Island were collected from January 1990 to December 1997 and the observations at Pontianak were made from November 1995 to July 1997. Power spectral techniques are used to study the amplitude and frequency variations of long-period oscillations as a function of height and time. A mean climatology of these variations taken from years 1990–1997 is presented. Strong peaks in zonal and meridional winds are found at tidal periods and for the quasi 2-day wave. Zonal spectra exhibit considerable power at periods of 3–10 days, with transient oscillations with periods near 3.5 day and 6.5 days being especially prominent. The 6.5-day wave is particularly strong during April and September. Examination of the phase differences obtained from cross-spectra between the two stations show that the 6.5-day wave is westward propagating with zonal wavenumber 1, while the 3.5 day wave is eastward propagating with wavenumber 1. The 6.5-day wave is identified as a manifestation of an unstable mode, while the 3.5-day wave is identified as an ultrafast Kelvin wave. There are significant longitudinal variations in the amplitudes and inferred momentum fluxes of the 3.5-day wave, amplitudes being larger in the Asian region than in the central Pacific.

Non-linear interaction of the quasi 2-day wave and long-term oscillations in the summer midlatitude mesopause region as seen from LF D1 wind measurements over Central Europe (Collm, 52oN, 15oE)

Abstract From night-time mesopause region wind measurements over Central Europe, the day-to-day variability of the measured quasi 2-day wave is investigated with respect to its correlation with summer planetary wave events. A 14-year dataset of summer winds is used. The results indicate that the 2-day wave is modulated by planetary waves, especially by the 16-day wave. Secondary frequencies that are expected, if a non-linear interaction between the waves is assumed, are found from regression analysis. Additionally, these secondary oscillations are modulated by the duration of the quasi 2-day wave event itself. Tertiary frequencies that belong to this modulation are also found from periodogram analysis. The long-term dataset analysis shows that the non-linear interaction is a regular phenomenon that is frequently found in connection with planetary wave activity in the summer upper mesosphere and lower thermosphere.

Simultaneous observations of the 2-day wave at London (43°N, 81°W) and Saskatoon (52°N, 107°W) near 91 km altitude during the two years of 1993 and 1994

Abstract. Simultaneous observations are valuable in providing further insights into the character of the quasi 2-day wave. In this study we investigate the period and amplitude for the quasi 2-day wave near 91 km using MF radars at London and Saskatoon, Canada, and in addition look at possible values of the zonal wave number. The results of the present study bring out certain new aspects of the quasi 2-day wave at mid-latitudes in the Northern Hemisphere. In particular we show that the period of the quasi 2-day wave determined from our study (specially at large amplitudes) is smaller (46–47 h) than the 51–52 h period often suggested by other Northern Hemisphere results, and that the periods also showed variability as a function of time. We also draw attention to the annual variability, and especially highlight the occurrence of the wave in non-summer months. Our observations show significant wave correlation between the London and Saskatoon sites during time intervals of strong 2-day wave activity. These results suggest that the 2-day waves of 1993/4 are westward propagating waves of zonal wave number 3, although sometimes the zonal wave number 5 is also indicated (specially at large amplitudes). Our study also contributes additional mid-latitude geographical data which should aid in developing a better picture of the quasi 2-day wave.

The quasi 2-day wave as seen from D1 LF wind measurements over central Europe (52 °N, 15 °E) at Collm

Abstract The quasi 2-day wave at mesopause heights over Central Europe is investigated through a longterm study of mesopause winds at 95 km altitude at Collm, Germany. The wave is found in every year with a maximum amplitude in the months July and August. The zonal and meridional components have nearly the same amplitude and the phase difference between the horizontal components varies roughly between phase and quadrature. The northward maximum of the wind is found to occur preferentially near noon, thus, the phase is possibly locked to the solar tides. The period of the wave is changing during the respective events, so that as the amplitude grows the period shortens and vice versa. A dependence of the amplitude of the quasi 2-day wave on the solar cycle is found in such a way that the amplitude is larger during solar maximum. This can be explained by a dependence of the wave propagation on the mean wind, which in the lower mesopause region is directed towards the west in summer and is stronger during solar maximum. The amplitude of the quasi 2-day wave is correlated with the prevailing wind, but this result is only at a low significance level.

The quasi 2-day wave at Durham (43°N): solar and magnetic effects

A quasi 2-day oscillation has been observed in the meteor winds at Durham since 1970. On a four-day basis the oscillation occurs throughout the year with amplitudes of 10 m s −1 and standing wave or evanescent ( λ z > 150 km) behavior with height. During late summer the oscillation increases in amplitude to ~30 m s −1 with increased phase coherence. When analyzed as a 48 h component the time of maximum of the North-South oscillation prefers the value 15 h LST implying some interaction with the solar tides. The amplitude of the 2-day component is correlated with the daily magnetic index A p indicating magnetic activity as a possible forcing for this oscillation.

Simultaneous observations of the quasi 2-day wave at Mawson, Antarctica, and Adelaide, South Australia

Observations of the Austral quasi 2-day wave at Mawson, Antarctica (67°S, 63°E) are presented and compared with those from Adelaide (35°S, 138°E). The data were obtained from partial-reflection radars which have been measuring winds continuously since mid-1984, and the results presented here are the first to record the 2-day wave in middle atmosphere winds from Mawson. They show that 2-day period oscillations of 10–15 m s −1 are a regular feature of the high latitude southern hemisphere summer. The wide longitude and latitude separation of the radar stations permits estimates of propagation velocity and latitude phase structure, and results are consistent with the passage of a westward travelling Rossby-gravity (3, 3) wave.

Long period wind oscillations in the 80–110 km altitudes observed by the Kyoto meteor radar in 1983–1985

During the MAP period, the Kyoto meteor radar has almost continuously monitored the wind fields in the 80–110 km altitudes. Wind oscillations with various periods ranging from 2 to 20 days are detected. The period of the quasi 2-day wave in 1983 was 2.2 days in summer months but became as short as about 2.0 days in autumn. Antisymmetry in phase profiles is detected by comparing the behavior of the quasi 2-day wave simultaneously observed at Adelaide and Kyoto.

Simultaneous observations of the quasi 2-day wave in the northern and southern hemispheres

Abstract—Observations of winds in the mesosphere and lower thermosphere made in July and August 1980 at Sheffield (53°N, 2°W), Townsville (19°S, 147°E) and Adelaide (35°S, 138°E) are compared. A quasi 2-day oscillation is evident in both the Sheffield and Townsville data, which suggests a significant cross-equatorial leakage of the wave from the summer to the winter hemisphere. A mean period of near 50 h and a vertical wavelength of about 50 km are found.