Diurnal Variations in the Summer Wind Field Over the Central United States

Hering, Wayne S.; Borden, Thomas R.

doi:10.1175/1520-0469(1962)019<0081:dvitsw>2.0.co;2

Cited by 42 publications

(25 citation statements)

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“…These features appear repeatedly in other years and are most prevalent during the warm season. Such upper-level wind field oscillations within the Great Plains NLLJ region have been reported by Hering and Borden (1962), Helfand and Schubert (1995), Higgins et al (1997), and Jiang et al (2007). Helfand and Schubert (1995) ascribe the diurnal wind reversal at 4-6 km AGL to thermal uplift, which they call a ''thermal chimney,'' where warmer air from below is ''ventilated'' aloft during the day, inducing convergence at low levels and divergence in the middle levels, with the reverse circulation forming at night.…”

Section: ) Great Plains Nlljmentioning

confidence: 99%

Global Distribution and Characteristics of Diurnally Varying Low-Level Jets

et al. 2010

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This study documents the global distribution and characteristics of diurnally varying low-level jets (LLJs), including their horizontal, vertical, and temporal structure, with a special emphasis on highlighting the underlying commonalities and unique qualities of the various nocturnal jets. Two tools are developed to accomplish this goal. The first is a 21-yr global reanalysis performed with the fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) using a horizontal grid spacing of 40 km. A unique characteristic of the reanalysis is the availability of hourly three-dimensional output, which permits the full diurnal cycle to be analyzed. Furthermore, the horizontal grid spacing of 40 km better resolves many physiographic features that host LLJs than other widely used global reanalyses. This makes possible a detailed examination of the systematic onset and cessation of the jets, including time-height representations of the diurnal cycle. The second tool is an index of nocturnal LLJ (NLLJ) activity based upon the vertical structure of the wind's temporal variation, where the temporal variation is defined in local time. The first available objectively constructed global maps of recurring NLLJs are created from this index, where the various NLLJs can be simultaneously viewed at or near their peak time. These maps not only highlight all of the locations where NLLJs are known to recur, but they also reveal a number of new jets.The authors examine the basic mechanisms that give rise to the NLLJs identified in four disparate locations, each having a profound influence on the regional climate. The first, the extensively studied Great Plains NLLJ, is used to confirm the veracity of the global analysis and the index of NLLJ activity. It also provides context for three of the many newly identified NLLJs: 1) Tarim Pendi in northwest China; 2) Ethiopia in eastern Africa; and 3) Namibia-Angola in southwest Africa. Jets in these four regions illustrate the variety of physiographic and thermal forcing mechanisms that can produce NLLJs.

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Section: ) Great Plains Nlljmentioning

confidence: 99%

Global Distribution and Characteristics of Diurnally Varying Low-Level Jets

et al. 2010

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“…This upper-level center is situated relatively higher in the AGCM simulation. This out-of-phase diurnal oscillation between the low-level and upper-level wind field has also been reported by Hering and Borden (1962; station observation), Helfand and Schubert (1995; AGCM simulation) and Higgins et al (1997;profiler observation). Helfand and Schubert (1995) ascribed this phenomenon to a "thermal chimney" effect, in which daytime heating/nighttime cooling over the high terrain plays an important role for the out-of-phase diurnal oscillation between low-level and upper-level wind.…”

Section: Agcm-simulated Lljmentioning

confidence: 99%

“…The jet exhibits strong diurnal oscillation, with the strongest wind speed mostly occurring during the night. This Great Plains LLJ has been intensively documented during the past decades (e.g., Means 1952Means , 1954Hering and Borden 1962;Izumi and Barad 1963;Hoecker 1963Hoecker , 1965Parish et al 1988;Frisch et al 1992;Mitchell and Arritt 1995; and many others). Bonner (1968) provides a comprehensive study on the climatology of the LLJ.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of the Great Plains Low-Level Jet as Simulated in an AGCM

Jiang

Held

Ploshay

2007

Journal of the Atmospheric Sciences

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A model diagnosis has been performed on the nocturnal Great Plains low-level jet (LLJ), which is one of the key elements of the warm season regional climate over North America. The horizontal-vertical structure, diurnal phase, and amplitude of the LLJ are well simulated by an atmospheric general circulation model (AGCM), thus justifying a reevaluation of the physical mechanisms for the formation of the LLJ based on output from this model. A diagnosis of the AGCM data confirms that two planetary boundary layer (PBL) processes, the diurnal oscillation of the pressure gradient force and of vertical diffusion, are of comparable importance in regulating the inertial oscillation of the winds, which leads to the occurrence of maximum LLJ strength during nighttime. These two processes are highlighted in the theories for the LLJ proposed by Holton (1967) and Blackadar (1957). A simple model is constructed in order to study the relative roles of these two mechanisms. This model incorporates the diurnal variation of the pressure gradient force and vertical diffusion coefficients as obtained from the AGCM simulation. The results reveal that the observed diurnal phase and amplitude of the LLJ can be attributed to the combination of these two mechanisms. The LLJ generated by either Holton's or Blackadar's mechanism alone is characterized by an unrealistic meridional phase shift and weaker amplitude.It is also shown that the diurnal phase of the LLJ exhibits vertical variations in the PBL, more clearly at higher latitudes, with the upper PBL wind attaining a southerly peak several hours earlier than the lower PBL. The simple model demonstrates that this phase tilt is due mainly to sequential triggering of the inertial oscillation from upper to lower PBL when surface cooling commences after sunset. At lower latitudes, due to the change of orientation of prevailing mean wind vectors and the longer inertial period, the inertial oscillation in the lower PBL tends to be interrupted by strong vertical mixing in the following day, whereas in the upper PBL, the inertial oscillation can proceed in a low-friction environment for a relatively longer duration. Thus, the vertical phase tilt initiated at sunset is less evident at lower latitudes.

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“…Three decades later, Hering andBorden (1962), Bonner (1968) and further examined and quantified the diurnal wind variations of the central United States. Hering and Borden (1962) noted that the diurnal wind system extended across much of the central tier of the country with good spatial consistency in the pattern.…”

Section: Windmentioning

confidence: 66%

“…Hering and Borden (1962) noted that the diurnal wind system extended across much of the central tier of the country with good spatial consistency in the pattern.…”

Section: Windmentioning

confidence: 99%

Decadal-Scale Trends in Transition Weather Types and Atmospheric Circulation

Hondula

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Diurnal Variations in the Summer Wind Field Over the Central United States

Cited by 42 publications

References 0 publications

Global Distribution and Characteristics of Diurnally Varying Low-Level Jets

Global Distribution and Characteristics of Diurnally Varying Low-Level Jets

Mechanisms of the Great Plains Low-Level Jet as Simulated in an AGCM

Decadal-Scale Trends in Transition Weather Types and Atmospheric Circulation

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