8.2: Troughs and Ridges
- Page ID
- 45360
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Waves in the Jet Stream
The collection of blue height lines on an upper-level map, such as Figure 8.2.1, is not straight as they extend across the Continental United States. Rather, they create a series of waves called troughs and ridges. Figure 8.2.1 shows an upper-level weather map with troughs and ridges.
- Ridges: When the lines form what appears to be a hill that moves North, peaks, and then dips back South, that is called a ridge. Along the ridges, warmer air is pushed northward, creating a giant hump at the 500 millibar level.
- Troughs: When the lines form what appears to be a dip/depression/”u” shape that moves South, bottoms out, and then travels back North, that is called a trough. Along the troughs, cooler air is pushed south, creating what appears to be a giant valley at the 500 millibar level.
Remember, these troughs and ridges may extend over the ocean. We can assume that the height contours will eventually return to their zonal (east-west) orientation beyond the map. Let's apply this knowledge to Figure 8.2.2, which is a 500 millibar map for 1200 UTC on February 28, 2025.
- The weather map in Figure 8.2.2 exhibits a pattern that features:
- A giant trough on the West Coast of the United States
- Zonal (flat) West-East flow across the entire United States
- A giant ridge on the West Coast and a trough in the Midwest and the East Coast
Upper-Level Winds and the Pressure Gradient Force
Let's examine the wind barbs on Figure 8.2.1. Because there is little to no friction in the upper atmosphere, winds aloft tend to be much faster than at the surface. While this isn’t always true, it’s a good assumption for this course and in general.
- The wind barbs tend to __________ to the blue height lines.
- be parallel
- intersect at large angles or are nearly perpendicular
- Winds tend to be stronger when: (Hint: Compare wind speeds over Minnesota and Michigan to wind speeds over California and Nevada)
- The height lines are closer together
- The height lines are further apart
- Your answer to question 15 __________ with the concept that surface winds are faster when isobars are closer together (from Investigation 7), indicating that the increased speed of the wind in both situation is _________ caused by the pressure gradient force.
- agrees; indeed
- disagrees; not
- disagrees; indeed
- agrees; not
Thus, we realize that forces such as the Pressure Gradient Force and the Coriolis Force have the same impact on the wind speed and direction, regardless of elevation.