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 are 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 a diagram with troughs and ridges labeled).
- 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 ridges, warmer air is pushed to the North, creating (what literally is) 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 troughs, cooler air is pushed to the south, creating what looks like (and what literally is) a giant valley at the 500 millibar level.
Let's apply this knowledge to Figure 8.2.2, which is a 500 millibar map for 1200 UTC on February 28, 2025.
- Figure 8.2.2 exhibited a pattern that featured:
- 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 on the East Coast.
Upper-Level Winds and the Pressure Gradient Force
Look at the wind barbs present 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 (this isn’t 100% true all of the time, but it’s a good guideline for this course and in general). Look at the pattern of winds relative to the blue height lines.
- The Wind barbs tend to ________________________________ to the blue height lines.
- Be parallel
- Intersect at large angles… nearly perpendicular
- Winds tend to be stronger when (hint: Compare wind speeds over Minnesota and Michigan to wind speeds over California and Nevada):
- Height lines are closer together
- 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.
- Is In Agreement; Indeed
- Is In Opposition; Not
- Is In Opposition; Indeed
- Is In Agreement; Not
HINT: The point of question 16 is that other than friction, the other forces have the same impact on the wind, regardless of elevation.