METEOROLOGICAL ROCKET SOUNDING FOR ATMOSPHERIC RESEARCH AND MONITORING OF GEOPHYSICAL CONDITIONS

The brief description of technical specification of meteorological rockets used at Roshydromet stations, including the exposition of the MERA new meteorological rocket with a lift up to 100 km, MRS 100 rocketsonde, onboard measuring and service equipment, is presented. The technique for measuring atmospheric parameters and the results of investigating long-term variability of temperature and wind in the stratosphere and mesosphere according to long-term (1969-1995) data of meteorological rocket sounding at Volgograd station are considered. It is shown that in the altitude range from 25 to 75 km, trends in temperature and wind speed over Volgograd station for 1969-1995 are nonlinear and, at most altitudes, nonmonotonic. An increase with altitude in the range of trend variations in the analyzed parameters during the surveyed period is discovered: up to 15-19 K in the lower and middle mesosphere for temperature, up to 15 m/s at the stratopause for the zonal component of wind speed, up to 10 m/s in the lower mesosphere for its meridional component.

Verification of reanalysis data for the tropical zone of the Indian ocean. Part 2. Characteristics of the averaged seasonal cycle and interannual variability

The aim of the study is to evaluate the performance of ORAS5/SODA3/GLORYS re-analyses using the RAMA in the tropical Indian Ocean. To assess the reproducibility of the seasonal cycle and characteristics of interannual variability, we used the data on the potential temperature, salinity, and zonal component of the current vector obtained south of the equator for the period 2010–2014. It is shown that at 55°E south of the equator, the GLORYS re-analysis better reproduces the five-year averaged seasonal cycle and interannual variability than the SODA3 and ORAS5 re-analyses.

Multi-year observations of gravity wave momentum fluxes at low and middle latitudes inferred by all-sky meteor radar

We have applied a modified composite day analysis to the Hocking (2005) technique to study gravity wave (GW) momentum fluxes in the mesosphere and lower thermosphere (MLT). Wind measurements from almost continuous meteor radar observations during June 2004–December 2008 over São João do Cariri (Cariri; 7° S, 36° W), April 1999–November 2008 over Cachoeira Paulista (CP; 23° S, 45° W), and February 2005–December 2009 over Santa Maria (SM; 30° S, 54° W) were used to estimate the GW momentum fluxes and variances in the MLT region. Our analysis can provide monthly mean altitude profiles of vertical fluxes of horizontal momentum for short-period (less than 2–3 h) GWs. The averages for each month throughout the entire data series have shown different behavior for the momentum fluxes depending on latitude and component. The meridional component has almost the same behavior at the three sites, being positive (northward), for most part of the year. On the other hand, the zonal component shows different behavior at each location: it is positive for almost half the year at Cariri and SM but predominantly negative over CP. Annual variation in the GW momentum fluxes is present at all sites in the zonal component and also in SM at 89 km in the meridional component. The seasonal analysis has also shown a 4-month oscillation at 92.5 km over SM in the zonal component and over CP at the same altitudes but for the meridional component.

Evolution of the Lorenz Energy Cycle in the Intertropical Convergence Zone in the South American Sector of the Atlantic Ocean

The intertropical convergence zone (ITCZ) in the South American sector of the Atlantic Ocean is identified using outgoing longwave radiation (OLR) data in order to investigate the evolution of the Lorenz energy cycle in the region dominated by this large-scale feature. The NCEP reanalysis data are utilized to calculate the zonal and eddy components (denoted by Z and E, respectively) of kinetic energy K and available potential energy A (i.e., KZ, KE, AZ, and AE) and their conversions, on a daily basis. A wavelet decomposition of the time series is performed to detect long-term cycles/trends in the Atlantic ITCZ region. This work also investigates trends in sea surface temperature (SST) and sea level pressure (SLP) in the ITCZ region and connections between the ITCZ and the Southern Oscillation index (SOI). A strong annual cycle in all the energy components with high peaks in austral summer is observed. Approximately 91% of the zonal component of energy is contained on decadal or longer time scales. The annual and semiannual variabilities are significant and the synoptic-scale variability is also present. The zonal component of kinetic energy KZ presents a decreasing trend during the last 28 years, which means a weakening of trade winds in the region studied. The values of KZ and AE are significantly higher during the period 1982/83, indicating that the intense El Niño–Southern Oscillation (ENSO) and/or the El Chichón eruption may have affected the circulation in the ITCZ region. The 28-yr mean energy conversion and generation terms are in general weaker than in the hemispheric calculations but the energy conversions proceed in the same sense as in the hemispheric situation.

The 8-h tide in the mesosphere and lower thermosphere over Maui (20.75° N, 156.43° W)

Wind data collected by the Maui meteor radar (20.75° N, 156.43° W) are used to study the 8-h tide in the mesosphere and lower thermosphere (MLT) region at a low-latitude station. The data set spans the time interval from 19 May 2002 to 24 May 2007. Our results show that the 8-h tide is a regular and distinct feature over Maui. The meridional component of this wave is significantly larger than the zonal component. The meridional component exhibits a semiannual variation in amplitude, with peaks near the equinoxes, whereas the variation of the zonal component does not show this seasonal characteristic. The strongest wave motions mostly occur in the height range of 92–96 km near spring equinox (March) and at higher altitudes near autumn equinox (October). The vertical variations of 8-h tidal phase at Maui indicate an upward wave energy flux. The vertical wavelengths are ≥54 km in equinox months.

Energy Accumulation in Easterly Circumpolar Jets Generated by Two-Dimensional Barotropic Decaying Turbulence on a Rapidly Rotating Sphere

A series of numerical experiments on two-dimensional decaying turbulence is performed for a barotropic fluid on a rotating sphere. Numerical calculations have confirmed two important asymptotic features: emergence of the banded structure of zonal flows and their extreme latitudinal inhomogeneities in which kinetic energy is accumulated into the easterly circumpolar jets. The banded structure of zonal flows is established relatively early on in the initial stage. Later, after extended periods of time integration, only the circumpolar jets are intensified gradually, while there is no further evolution in the banded structure in the low and midlatitudes. Wave activity flux analysis illustrates that the initial vortices in the low and midlatitudes propagate poleward as Rossby waves and converge to produce easterly circumpolar flows. In association with this convergence, accumulation of the mean zonal component of kinetic energy proceeds. The tendency for the accumulation becomes strong as the rotation rate is increased, and nearly all of the kinetic energy is concentrated to the circumpolar flows in cases of rapid rotation. A theoretical model is constructed under the assumption that a circumpolar jet emerges around the latitude where the local Rhines scale is equal to the distance from the Pole, and that initial vortices at the lower latitudes contribute to the generation of the jets. The model describes the mean zonal component of kinetic energy and the averaged speed and width of the circumpolar jets as functions of the rotation rate, which agree satisfactorily with the numerical results.

Mean winds observed with Indian MST radar over tropical mesosphere and comparison with various techniques

Temporal variation of mean winds between the 65 to 85 km height region from the data collected over the course of approximately four years (1995–99), using the Indian MST radar located at Gadanki (13.5° N, 79.2° E), India is presented in this paper. Mesospheric mean winds and their seasonal variation in the horizontal and vertical components are presented in detail. Westward flows during each of the equinoxes and eastward flows during the solstices are observed in the zonal component. The features of the semi-annual oscillation (SAO) and the quasi-biennial oscillation (QBO) in the zonal component are noted. In the meridional component, contours reveal a northward motion during the winter and a southward motion during the summer. Large inter-annual variability is found in the vertical component with magnitudes of the order of ± 2 ms-1 . The MST observed winds are also compared with the winds observed by the MF radar located at Tirunelveli (8.7° N, 77.8° E), India, the High Resolution Doppler Imager (HRDI) onboard the Upper Atmospheric Research Satellite (UARS), and with the CIRA-86 model. A very good agreement is found between both the ground-based instruments (MST radar and MF radar) in the zonal component and there are few discrepancies in the meridional component. UARS/HRDI observed winds usually have larger magnitudes than the ground-based mean winds. Comparison of the MST derived winds with the CIRA-86 model in the zonal component shows that during the spring equinox and the summer, the winds agree fairly well, but there are a lot of discrepancies in the other seasons and the observed winds with the MST radar are less in magnitude, though the direction is same. The strengths and limitations in estimating reliable mesospheric mean winds using the MST radar are also discussed.Key words. Meteorology and atmospheric dynamics (general circulation; middle atmosphere dynamics; waves and tides)