scholarly journals Intra-seasonal Oscillations (ISO) of zonal-mean meridional winds and temperatures as measured by UARS

2005 ◽  
Vol 23 (4) ◽  
pp. 1131-1137 ◽  
Author(s):  
F. T. Huang ◽  
H. G. Mayr ◽  
C. A. Reber
Keyword(s):  
Meridional Wind ◽  
Mean Flow ◽  
Independent Evidence ◽  
Doppler Imager ◽  
Temperature Oscillations ◽  
Low Latitudes ◽  
Meridional Winds ◽  
Flow Interactions ◽  
Phase Variations ◽  
Seasonal Oscillations

Abstract. Based on an empirical analysis of measurements with the High Resolution Doppler Imager (HRDI) on the UARS spacecraft in the upper mesosphere (95km), persistent and regular intra-seasonal oscillations (ISO) with periods of about 2 to 4 months have recently been reported in the zonal-mean meridional winds. Similar oscillations have also been discussed independently in a modeling study, and they were attributed to wave-mean-flow interactions. The observed and modeled meridional wind ISOs were largely confined to low latitudes. We report here on an analysis of concurrent UARS temperature measurements, which produces oscillations similar to those seen in the meridional winds. Although the temperature oscillations are observed at lower altitudes (55km), their phase variations with latitude are qualitatively consistent with the inferred properties seen in the meridional winds and thus provide independent evidence for the existence of ISOs in the mesosphere.

scholarly journals Two-day wave structure and mean flow interactions observed by radar and High Resolution Doppler Imager

1999 ◽  
Vol 104 (D4) ◽  
pp. 3953-3969 ◽  
Author(s):  
David C. Fritts ◽  
Joseph R. Isler ◽  
Ruth S. Lieberman ◽  
Mark D. Burrage ◽  
Daniel R. Marsh ◽  
...  
Keyword(s):  
High Resolution ◽  
Wave Structure ◽  
Mean Flow ◽  
Doppler Imager ◽  
Flow Interactions

scholarly journals Thermal tides and studies to tune the mechanistic tidal model using UARS observations

1997 ◽  
Vol 15 (9) ◽  
pp. 1205-1220 ◽  
Author(s):  
V. A. Yudin ◽  
B. V. Khattatov ◽  
M. A. Geller ◽  
D. A. Ortland ◽  
C. McLandress ◽  
...  
Keyword(s):  
Initial Guess ◽  
Model Parameters ◽  
Mean Flow ◽  
Tidal Model ◽  
Doppler Imager ◽  
Imaging Interferometer ◽  
Meridional Winds ◽  
Flow Components ◽  
Thermal Tides ◽  
Best Fit

Abstract. Monthly simulations of the thermal diurnal and semidiurnal tides are compared to High-Resolution Doppler Imager (HRDI) and Wind Imaging Interferometer (WINDII) wind and temperature measurements on the Upper-Atmosphere Research Satellite (UARS). There is encouraging agreement between the observations and the linear global mechanistic tidal model results both for the diurnal and semidiurnal components in the equatorial and mid-latitude regions. This gives us the confidence to outline the first steps of an assimilative analysis/interpretation for tides, dissipation, and mean flow using a combination of model results and the global measurements from HRDI and WINDII. The sensitivity of the proposed technique to the initial guess employed to obtain a best fit to the data by tuning model parameters is discussed for the January and March 1993 cases, when the WINDII day and night measurements of the meridional winds between 90 and 110 km are used along with the daytime HRDI measurements. Several examples for the derivation of the tidal variables and decomposition of the measured winds into tidal and mean flow components using this approach are compared with previous tidal estimates and modeling results for the migrating tides. The seasonal cycle of the derived diurnal tidal amplitudes are discussed and compared with radar observation between 80 and 100 km and 40°S and 40°N.

scholarly journals Wave-mean flow interactions in the upper atmosphere

1973 ◽  
Vol 4 (1-4) ◽  
pp. 327-343 ◽  
Author(s):  
Richard S. Lindzen
Keyword(s):  
Upper Atmosphere ◽  
Mean Flow ◽  
Flow Interactions

Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings

2021 ◽  
Author(s):  
Masaru Yamamoto ◽  
Takumi Hirose ◽  
Kohei Ikeda ◽  
Masaaki Takahashi
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Circulation Model ◽  
Stationary Wave ◽  
Static Stability ◽  
Small Scale ◽  
Mean Flow ◽  
Short Period ◽  
Low Latitudes ◽  
Thermal Tides

<p>General circulation and waves are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography. This model has been developed by Ikeda (2011) at the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, and was used in Yamamoto et al. (2019, 2021). In the wind and static stability structures similar to the observed ones, the waves are investigated. Around the cloud-heating maximum (~65 km), the simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m/s<sup></sup>with rates of 0.2–0.5 m/s/(Earth day) via both horizontal and vertical momentum fluxes at low latitudes. Over the high mountains at low latitudes, the vertical wind variance at the cloud top is produced by topographically-fixed, short-period eddies, indicating penetrative plumes and gravity waves. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the night-side than on the dayside at the cloud top. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves. Around the cloud bottom, the 9-day super-rotation of the zonal mean flow has a weak equatorial maximum and the 7.5-day Kelvin-like wave has an equatorial jet-like wind of 60-70 m/s. Because we discussed the thermal tide and topographically stationary wave in Yamamoto et al. (2021), we focus on the short-period eddies in the presentation.</p>

scholarly journals Effects of the midnight temperature maximum observed in the thermosphere–ionosphere over the northeast of Brazil

2017 ◽  
Vol 35 (4) ◽  
pp. 953-963 ◽  
Author(s):  
Cosme Alexandre O. B. Figueiredo ◽  
Ricardo A. Buriti ◽  
Igo Paulino ◽  
John W. Meriwether ◽  
Jonathan J. Makela ◽  
...  
Keyword(s):  
Relative Intensity ◽  
Lower Thermosphere ◽  
Meridional Wind ◽  
Peak Height ◽  
Neutral Wind ◽  
F Region ◽  
Early Evening ◽  
Neutral Temperature ◽  
Constant Height ◽  
Meridional Winds

Abstract. The midnight temperature maximum (MTM) has been observed in the lower thermosphere by two Fabry–Pérot interferometers (FPIs) at São João do Cariri (7.4° S, 36.5° W) and Cajazeiras (6.9° S, 38.6° W) during 2011, when the solar activity was moderate and the solar flux was between 90 and 155 SFU (1 SFU  =  10−22 W m−2 Hz−1). The MTM is studied in detail using measurements of neutral temperature, wind and airglow relative intensity of OI630.0 nm (referred to as OI6300), and ionospheric parameters, such as virtual height (h′F), the peak height of the F2 region (hmF2), and critical frequency of the F region (foF2), which were measured by a Digisonde instrument (DPS) at Eusébio (3.9° S, 38.4° W; geomagnetic coordinates 7.31° S, 32.40° E for 2011). The MTM peak was observed mostly along the year, except in May, June, and August. The amplitudes of the MTM varied from 64 ± 46 K in April up to 144 ± 48 K in October. The monthly temperature average showed a phase shift in the MTM peak around 0.25 h in September to 2.5 h in December before midnight. On the other hand, in February, March, and April the MTM peak occurred around midnight. International Reference Ionosphere 2012 (IRI-2012) model was compared to the neutral temperature observations and the IRI-2012 model failed in reproducing the MTM peaks. The zonal component of neutral wind flowed eastward the whole night; regardless of the month and the magnitude of the zonal wind, it was typically within the range of 50 to 150 m s−1 during the early evening. The meridional component of the neutral wind changed its direction over the months: from November to February, the meridional wind in the early evening flowed equatorward with a magnitude between 25 and 100 m s−1; in contrast, during the winter months, the meridional wind flowed to the pole within the range of 0 to −50 m s−1. Our results indicate that the reversal (changes in equator to poleward flow) or abatement of the meridional winds is an important factor in the MTM generation. From February to April and from September to December, the h′F and the hmF2 showed an increase around 18:00–20:00 LT within a range between 300 and 550 km and reached a minimal height of about 200–300 km close to midnight; then the layer rose again by about 40 km or, sometimes, remained at constant height. Furthermore, during the winter months, the h′F and hmF2 showed a different behavior; the signature of the pre-reversal enhancement did not appear as in other months and the heights did not exceed 260 and 350 km. Our observation indicated that the midnight collapse of the F region was a consequence of the MTM in the meridional wind that was reflected in the height of the F region. Lastly, the behavior of the OI6300 showed, from February to April and from September to December, an increase in intensity around midnight or 1 h before, which was associated with the MTM, whereas, from May to August, the relative intensity was more intense in the early evening and decayed during the night.

scholarly journals New results on equatorial thermospheric winds and temperatures from Ethiopia, Africa

2017 ◽  
Vol 35 (2) ◽  
pp. 333-344 ◽  
Author(s):  
Fasil Tesema ◽  
Rafael Mesquita ◽  
John Meriwether ◽  
Baylie Damtie ◽  
Melessew Nigussie ◽  
...  
Keyword(s):  
Local Time ◽  
Zonal Wind ◽  
Meridional Wind ◽  
Local Times ◽  
Maximum Speed ◽  
Wind Speeds ◽  
Early Evening ◽  
Meridional Winds ◽  
Thermospheric Winds ◽  
Wind Surge

Abstract. Measurements of equatorial thermospheric winds, temperatures, and 630 nm relative intensities were obtained using an imaging Fabry–Perot interferometer (FPI), which was recently deployed at Bahir Dar University in Ethiopia (11.6° N, 37.4° E, 3.7° N magnetic). The results obtained in this study cover 6 months (53 nights of useable data) between November 2015 and April 2016. The monthly-averaged values, which include local winter and equinox seasons, show the magnitude of the maximum monthly-averaged zonal wind is typically within the range of 70 to 90 ms−1 and is eastward between 19:00 and 21:00 LT. Compared to prior studies of the equatorial thermospheric wind for this local time period, the magnitude is considerably weaker as compared to the maximum zonal wind speed observed in the Peruvian sector but comparable to Brazilian FPI results. During the early evening, the meridional wind speeds are 30 to 50 ms−1 poleward during the winter months and 10 to 25 ms−1 equatorward in the equinox months. The direction of the poleward wind during the winter months is believed to be mainly caused by the existence of the interhemispheric wind flow from the summer to winter hemispheres. An equatorial wind surge is observed later in the evening and is shifted to later local times during the winter months and to earlier local times during the equinox months. Significant night-to-night variations are also observed in the maximum speed of both zonal and meridional winds. The temperature observations show the midnight temperature maximum (MTM) to be generally present between 00:30 and 02:00 LT. The amplitude of the MTM was  ∼  110 K in January 2016 with values smaller than this in the other months. The local time difference between the appearance of the MTM and a pre-midnight equatorial wind was generally 60 to 180 min. A meridional wind reversal was also observed after the appearance of the MTM (after 02:00 LT). Climatological models, HWM14 and MSIS-00, were compared to the observations and the HWM14 model generally predicted the zonal wind observations well with the exception of higher model values by 25 ms−1 in the winter months. The HWM14 model meridional wind showed generally good agreement with the observations. Finally, the MSIS-00 model overestimated the temperature by 50 to 75 K during the early evening hours of local winter months. Otherwise, the agreement was generally good, although, in line with prior studies, the model failed to reproduce the MTM peak for any of the 6 months compared with the FPI data.

scholarly journals Dynamical and Synoptic Characteristics of Heavy Rainfall Episodes in Southern Brazil

2007 ◽  
Vol 135 (2) ◽  
pp. 598-617 ◽  
Author(s):  
Mateusda Silva Teixeira ◽  
Prakki Satyamurty
Keyword(s):  
Heavy Rainfall ◽  
Moisture Flux ◽  
Southern Brazil ◽  
Mean Flow ◽  
Pressure Center ◽  
Average Rainfall ◽  
Meridional Winds ◽  
The Mean ◽  
Low Level Jet ◽  
Atmospheric Variables

Abstract The dynamical and synoptic characteristics that distinguish heavy rainfall episodes from nonheavy rainfall episodes in southern Brazil are discussed. A heavy rainfall episode is defined here as one in which the 50 mm day−1 isohyet encloses an area of not less than 10 000 km2 in the domain of southern Brazil. One hundred and seventy such events are identified in the 11-yr period of 1991–2001. The mean flow patterns in the period of 1–3 days preceding the episodes show some striking synoptic-scale features that may be considered forerunners of these episodes: (i) a deepening midtropospheric trough in the eastern South Pacific approaches the continent 3 days before, (ii) a surface low pressure center forms in northern Argentina 1 day before, (iii) a northerly low-level jet develops over Paraguay 2 days before, and (iv) a strong moisture flux convergence over southern Brazil becomes prominent 1 day before the episode. A parameter called rainfall quantity, defined as the product of the area enclosed by the 50 mm day−1 isohyet and the average rainfall intensity, is correlated with fields of atmospheric variables such as 500-hPa geopotential and 850-hPa meridional winds. Significant lag correlations show that the anomalies of some atmospheric variables could be viewed as precursors of heavy rainfall in southern Brazil that can be explored for use in improving the forecasts.

Advancing the simulation of mesoscale eddies: Backscatter schemes in eddy-permitting ocean simulations

2021 ◽  
Author(s):  
Stephan Juricke ◽  
Sergey Danilov ◽  
Marcel Oliver ◽  
Nikolay Koldunov ◽  
Dmitry Sidorenko ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Large Scale ◽  
Mesoscale Eddy ◽  
Ocean Model ◽  
Mean Flow ◽  
Ocean Coupling ◽  
Climate Simulations ◽  
Flow Interactions ◽  
To Come ◽  
Eddy Dynamics

<p>Capturing mesoscale eddy dynamics is crucial for accurate simulations of the large-scale ocean currents as well as oceanic and climate variability. Eddy-mean flow interactions affect the position, strength and variations of mean currents and eddies are important drivers of oceanic heat transport and atmosphere-ocean-coupling. However, simulations at eddy-permitting resolutions are substantially underestimating eddy variability and eddy kinetic energy many times over. Such eddy-permitting simulations will be in use for years to come, both in coupled and uncoupled climate simulations. We present a set of kinetic energy backscatter schemes with different complexity as alternative momentum closures that can alleviate some eddy related biases such as biases in the mean currents, in sea surface height variability and in temperature and salinity. The complexity of the schemes reflects in their computational costs, the related simulation improvements and their adaptability to different resolutions. However, all schemes outperform classical viscous closures and are computationally less expensive than a related necessary resolution increase to achieve similar results. While the backscatter schemes are implemented in the ocean model FESOM2, the concepts can be adjusted to any ocean model including NEMO.</p>

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