Mean Winds and Momentum Fluxes over Jicamarca, Peru, during June and August 1987

Hitchman, Matthew H.; Bywaters, Kenneth W.; Fritts, David C.; Coy, Lawrence; Kudeki, Erhan; Sürücü, Fahri

doi:10.1175/1520-0469(1992)049<2372:mwamfo>2.0.co;2

Cited by 37 publications

(21 citation statements)

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“…However, the MU radar observations revealed that the momentum fluxes are generally less than 1 m 2 s −2 in 60–90 km altitude region [ Tsuda et al , 1990]. Zonal momentum fluxes of the order of 2–8 m 2 s −2 were reported using VHF radar observations over Jicamarca (12°S, 77°W) in the 70–85 km height region [ Hitchman et al , 1992]. The gravity wave momentum fluxes in the tropospheric regions were estimated to be around −0.15 to 0.25 m 2 s −2 [ Murayama et al , 1994].…”

Section: Resultsmentioning

confidence: 99%

A quantitative study on the role of gravity waves in driving the tropical Stratospheric Semiannual Oscillation

et al. 2007

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[1] Using a coordinated experimental observation under Middle Atmospheric Dynamics (MIDAS) program, an extensive study is carried out to quantify the role of gravity waves in driving the tropical Stratospheric Semiannual Oscillation (SSAO). Rayleigh lidar observations of middle atmospheric temperature over Gadanki (13.5°N, 79.2°E) and rocketsonde wind measurements over Trivandrum (8.5°N, 76.9°E) during the period November 2002 to June 2005 are used for the present study. Gravity waves with periods ranging from 2-4 hours and 0.5-1 hour are found to be dominant in the middle atmosphere throughout the observational period. The altitude profiles of momentum fluxes of gravity waves having these time periods are estimated and their seasonal variations are studied, which showed semiannual variation with maximum around equinoxes and minimum around solstitial months. The mean flow acceleration estimated from the divergence of momentum flux of gravity waves is compared with the mean flow acceleration observed using rocket measured zonal winds during three different cycles of SSAO. This comparison provided an opportunity to quantify the contribution of gravity waves toward generation of SSAO, which is found to be $30-50% of the observed acceleration during the evolution of the westerly phase of the SSAO. The present observations showed that the contribution of the gravity waves toward the westerly phase of SSAO varies significantly from cycle to cycle. The significance of the present results lies in quantifying the gravity wave-mean flow interaction during both easterly and westerly phases of SSAO for the first time over this tropical latitude.

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Section: Resultsmentioning

confidence: 99%

A quantitative study on the role of gravity waves in driving the tropical Stratospheric Semiannual Oscillation

et al. 2007

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“…At extratropical sites, mean values of momentum fluxes of ∼1-10 m 2 s −2 have been measured with mean forcing in the range ∼10-70 ms −1 d −1 that generally oppose the mean winds (Reid and Vincent, 1987;Fritts and Yuan, 1989;Tsuda et al, 1990;Nakamura et al, 1993). At the tropical Jicamarca radar site (12 • S) (Hitchman et al, 1992), momentum fluxes of 3766 F. S. Kuo et al: Studies of vertical fluxes of horizontal momentum proposed by Vincent (1984) was widely applied to distinguish what fractions of the gravity wave spectrum are propagating upward and downward. Usually, wave amplitudes and modulus of momentum fluxes are larger for atmospheric gravity waves having upward energy fluxes and propagate opposite to the mean wind in the upper middle atmosphere (Nakamura et al, 1993;Gavrilov et al, 1995Gavrilov et al, , 1996Gavrilov et al, , 1997Hall et al, 1995).…”

Section: Introductionmentioning

confidence: 98%

Studies of vertical fluxes of horizontal momentum in the lower atmosphere using the MU-radar

et al. 2008

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Abstract.We study the momentum flux of the atmospheric motions in the height ranges between 6 and 22 km observed using the MU radar at Shigaraki in Japan during a 3 day period in January 1988. The data were divided by double Fourier transformation into data set of waves with downward-phase-velocity and data set of waves with upward-phase-velocity for independent momentum flux calculation. The result showed that both the 72 h averaged upward flux and downward flux of zonal momentum were negative at nearly each height, meaning that the upward flux was dominated by westward propagating waves while the downward flux was dominated by eastward propagating waves. The magnitude of the downward flux was approximately a factor of 1.5 larger than the upward flux for waves in the 2∼7 h and 7∼24 h period bands, and about equal to the upward flux in the 10-30 min and 30 min-2 h period bands. It is also observed that the vertical flux of zonal momentum tended to be small in each frequency band at the altitudes below the jet maximum (10∼12 km), and the flux increased toward more negative values to reach a negative maximum at some altitude well above the jet maximum. Daily averaged flux showed tremendous variation: The 1st 24 h (quiet day) was relatively quiet, and the fluxes of the 2nd and 3rd 24 h (active days) increased sharply. Moreover, the upward fluxes of zonal momentum below 17 km in the quiet day for each period band (10∼30 min, 30 min∼2 h, 2∼7 h, and 7∼24 h) were dominantly positive, while the corresponding downward fluxes were dominantly negative, meaning that the zonal momentum below 17 km in each period band under study were dominantly eastward (propagating along the mean wind). In the active days, both the upward fluxes and Correspondence to: F. S. Kuo (fskuo@msa.vnu.edu.tw) downward fluxes in each frequency band were dominantly negative throughout the whole altitude range 6.1-18.95 km.

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“…In particular, Vincent and Reid (1983) developed a technique for ground-based radars to estimate radial velocity variances and corresponding momentum fluxes in the mesosphere and lower thermosphere (MLT) using dual co-planar narrow radar beams. This technique has since been widely used by HF and VHF radars (e.g., Reid and Vincent, 1987;Fritts and Vincent, 1987;Fukao et al, 1988;Reid et al, 1988;Fritts and Yuan, 1989;Fritts et al, 1990;Sato, 1990Sato, , 1993Sato, , 1994Tsuda et al, 1990;Fritts, 1990, 1991;Hitchman et al, 1992;Nakamura et al, 1993;Murayama et al, 1994;Vincent, 1993, 1998). Similar approaches have been extended to MF broad beam interferometric radars (Thorsen et al, 1997), incoherent scatter radars (ISRs) operating at VHF and UHF Fritts et al, 2006;Janches et al, 2006), and Doppler lidar systems (Acott, 2009).…”

Section: Introductionmentioning

confidence: 79%

Momentum flux determination using the multi-beam Poker Flat Incoherent Scatter Radar

et al. 2012

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Abstract. In this paper, we develop an estimator for the vertical flux of horizontal momentum with arbitrary beam pointing, applicable to the case of arbitrary but fixed beam pointing with systems such as the Poker Flat Incoherent Scatter Radar (PFISR). This method uses information from all available beams to resolve the variances of the wind field in addition to the vertical flux of both meridional and zonal momentum, targeted for high-frequency wave motions. The estimator utilises the full covariance of the distributed measurements, which provides a significant reduction in errors over the direct extension of previously developed techniques and allows for the calculation of an error covariance matrix of the estimated quantities. We find that for the PFISR experiment, we can construct an unbiased and robust estimator of the momentum flux if sufficient and proper beam orientations are chosen, which can in the future be optimized for the expected frequency distribution of momentumcontaining scales. However, there is a potential trade-off between biases and standard errors introduced with the new approach, which must be taken into account when assessing the momentum fluxes. We apply the estimator to PFISR measurements on 23 April 2008 and 21 December 2007, from 60-85 km altitude, and show expected results as compared to mean winds and in relation to the measured vertical velocity variances.

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Mean Winds and Momentum Fluxes over Jicamarca, Peru, during June and August 1987

Cited by 37 publications

References 0 publications

A quantitative study on the role of gravity waves in driving the tropical Stratospheric Semiannual Oscillation

A quantitative study on the role of gravity waves in driving the tropical Stratospheric Semiannual Oscillation

Studies of vertical fluxes of horizontal momentum in the lower atmosphere using the MU-radar

Momentum flux determination using the multi-beam Poker Flat Incoherent Scatter Radar

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