Thermal Wind Balance Questions and Answers

Answer: A

Identical wind profiles imply identical thermal winds, and since the thermal wind gives the temperature gradient, the gradient must be the same at both, which for the simplest interpretation means it is zero across the region. Absolute surface temperatures are not determined, humidity is unrelated, and a front between the stations would produce very different shears rather than identical ones.

Answer: B

The thermal wind is defined as that difference, and it blows along the layer mean isotherms with cold air on its left in the northern hemisphere. The gradient and geostrophic winds are actual balanced flows at a single level, and the ageostrophic wind is the departure of the real wind from balance. Keeping the four apart is the foundation of balanced flow analysis.

Answer: C

Barotropy means density depends on pressure alone, so the two families of surfaces coincide and there is no horizontal temperature gradient and hence no thermal wind. Baroclinicity is the opposite case and is where the available potential energy of mid-latitude weather resides. Isentropic and conditionally unstable describe quite different properties of the vertical structure.

Answer: D

The derivation begins with geostrophic balance in pressure coordinates, differentiates it with respect to pressure, substitutes the hydrostatic relation to introduce temperature, and finally integrates across the layer to obtain the accumulated wind change, giving 2, 3, 1, 4. Following the sequence once makes clear why the result contains a logarithm of the pressure ratio and why virtual temperature appears rather than actual temperature. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: A

Thickness measures layer mean virtual temperature, the thermal wind is the shear of the geostrophic wind, and baroclinicity describes intersecting pressure and density surfaces. The three are linked in a chain, since baroclinicity implies a thickness gradient which implies a thermal wind, and seeing them as one chain rather than three definitions makes the topic considerably easier to hold in mind.

Answer: B

In the northern hemisphere veering means warm advection and backing means cold advection, while in the southern hemisphere the sense reverses so that veering means cold advection. The reversal follows from the sign of the Coriolis parameter, which puts warm rather than cold air on the left of the thermal wind south of the equator. Stating the rule with its hemisphere attached avoids the commonest error.

Answer: C

Subtracting the geostrophic wind vectors read from two constant pressure charts gives the thermal wind for the layer between them directly. Equivalently, the thickness chart for that layer gives the same information in one field, which is why thickness charts are drawn. Two surface charts give a tendency rather than a shear, and a satellite image carries no wind information of the required kind.

Answer: D

A thickness chart displays the difference field directly, so the thermal wind is read from its contour spacing exactly as a geostrophic wind is read from a height chart. That saves the vector subtraction and makes the temperature structure immediately visible. The same observations are needed either way, latitude is still required for the magnitude, and no chart gives the wind at intermediate levels without further assumption. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: A

A front is a concentrated temperature gradient, so it appears on a thickness chart as a band of tightly packed contours, sometimes called a thermal ribbon. The associated thermal wind is correspondingly strong, which is the frontal jet. A closed high thickness centre is a warm air mass, widely spaced contours indicate a uniform air mass, and a col in thickness is a region of weak thermal gradient rather than a front. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Answer: B

Forecasters speak of the thermal ribbon or thermal wind maximum where thickness contours pack together, and the upper jet lies along it. Identifying the ribbon is a standard step in locating the baroclinic zone in which development is most likely. Troughs and ridges are features of the height field, and a dry intrusion is a signature of descending stratospheric air seen in satellite imagery.