Frontogenesis


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Related to Frontogenesis: frontolysis

frontogenesis

[¦frən·tō¦jen·ə·səs]
(meteorology)
The initial formation of a frontal zone or front.
The increase in the horizontal gradient of an air mass property, mainly density, and the formation of the accompanying features of the wind field that typify a front.

Frontogenesis

 

the formation of a front, that is, the transformation of a broad transition zone between two air masses of the troposphere into an abrupt front. Frontogenesis is characterized by an increase in the horizontal temperature gradients and air humidity in the transition zone and by a more or less abrupt change in wind velocity. Kinematic frontogenesis, which is most common, occurs in the field of a wind that brings small particles of air of different temperatures close together. Topographical frontogenesis is sometimes observed as a result of the effect on the air of an abrupt change in the temperature of the underlying surface.

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In this article, we investigate the differences between two different quantities ([theta] and [[theta].sub.e]) and three functions (magnitude of the horizontal gradient, thermal front parameter, and frontogenesis) based on global reanalyses using a gridpoint-based method of identifying fronts described below.
To help visualize the importance of the moisture in the diagnostic fields involving [[theta].sub.e] without the influence of the temperature field, we compute the same three functions (magnitude of the gradient, thermal front parameter, and frontogenesis) using the specific humidity q at 850 hPa (Fig.
Climatologies are constructed for the six different frontal diagnostics discussed earlier: magnitude of the gradient, thermal front parameter, and frontogenesis for 850-hPa potential temperature and equivalent potential temperature (Figs.
Another way to show that the moisture field is affecting the climatologies involving [[theta].sub.e] is to compute the same three functions (magnitude of the gradient, thermal front parameter, and frontogenesis) using the specific humidity q at 850 hPa (Fig.
* The advantages and disadvantages of two thermodynamic quantities ([theta] and [[theta].sub.e]) and three functions (magnitude of the horizontal gradient, thermal front parameter, and frontogenesis) were reviewed in the text and summarized in Table 2.
* The Petterssen frontogenesis function using [theta] was effective for identifying midlatitude fronts, although may have quite a bit of alongfront variability in individual cases.
Given that Petterssen frontogenesis represents the process of frontal formation (i.e., isotherms being concentrated in the horizontal by the horizontal wind), it can be a useful tool for the analysis of fronts in operational forecasting and climatological analysis, as well as for research where its usage is already common (e.g., Keyser et al.
If the community requires fronts to have temperature gradients as the synoptic-dynamic literature and synoptic experience imply, then fronts should be a subset of airmass boundaries with a requisite thermal gradient and possibly also Petterssen frontogenesis along it.
Schultz, 2005: Contraction rate and its relationship to frontogenesis, the Lyapunov exponent, fluid trapping, and airstream boundaries.
Bretherton, 1972: Atmospheric frontogenesis models: Mathematical formulation and solutions.
Shapiro, 1986: Diagnosis of the role of vertical deformation in a two-dimensional primitive equation model of upper-level frontogenesis. J.
Caption: Figure 20: Simulated (12km) 850hPa streamlines, potential vorticity, and 700hPa frontogenesis on 0600 UTC 12 February 2010 for (a-b) control experiment, (c-d) terrain reduction experiment, (e-f) no microphysics heating experiment, and (g-h) no surface flux experiment.