ENSC 408: Lab 4 Hodographs October 1st, 2019

Lab 2 Marks

Good job overall!

Some Comments: • Areas of precipitation too large, watch out for stations reporting weather with symbols similar to those for precip. (clouds, mist, etc..) • You can use the front locations as well to help locate areas of precip. • Ex. Typically there is precip. in front of a cold front, but a dry band directly behind it • Contours could be smoother, nothing wrong with going back over an area you have detailed in and smoothing out unnecessary kinks • When discussing the air-masses (#6), be sure to talk about average features other than (Dew-point temperature, speed/direction) Low Temp. (C) High Temp. (C) Precipitation (no/yes/type)

Observed 5 9 1 Forecasted 7 14 1 Class Average 7 12 1 Class 6 10 1 5 13 1 8 10 1 7 11 1 6 14 1 7 14 1 8 12 1

Weather Forecasting Results

Average Score: 5 / 10

Presentation Past Wx Current/Future Wx Date Weather Sep 24 Selina Mabel Discussion Oct 1 Adele Selina Today @ 10 am Oct 8* -- -- • Presenters: Adele & Selina

Oct 15 Aaron Andy Next Week Oct 22 Mabel Aaron • No Labs! (Midterm*) Oct 29 Andy Adele Source: https://www.weather.gov/media/lmk/soo/Hodographs_Wind-Shear.pdf

Hodographs

Objective: • To learn techniques to study vertical atmospheric structure using a hodograph (plotting wind speed and direction with height) Materials: 1. A blank hodograph 2. Pencil, ruler Useful for: • Detecting nearby changes in air masses (fronts) based on the ‘turning’ of the with height • Determining ‘thermal wind’, relating vertical to horizontal temperature gradients

Source: Stull, R (2017) Veering & Backing Veering Winds Backing Winds Winds

Veering Winds • Winds which turn clockwise with height Unidirectional Winds • Associated with Warm Air (WAA) (i.e. warm fronts) • Stronger winds/veering -> greater advection Backing Winds • Winds which turn counter- clockwise with height • Associated with Cold Air Advection (CAA) (i.e. cold fronts) • Stronger winds/backing -> greater advection

Source: http://www.geosci.sfsu.edu/geosciences/classes/m500/Helicity/Straight_Curved.html

Ignore the red and blue Detecting Frontal lines, these are the past Mixing Zones and future hodographs

Frontal mixing zone • Location where mixing occurs on the boundary (fronts) between airmasses • Looking for a relatively long section (high wind shear) on the plotted hodograph, with inflection points (‘x’) on either end • These inflection points mark areas of strong vertical wind shear • Changing wind velocity/direction with height Focus on the black line for this example…

Source: https://cameronnixonphotography.wordpress.com/research/the-storm-relative-hodograph/ Detecting Frontal Motion

Orange line marks the In this case, the front is Frontal motion (direction and speed) position of the front.. moving East, at a rate of ~4 units • The vector from the origin, normal (perpendicular) to the frontal mixing zone gives the direction and speed of travel for the frontal mixing zone • Length of the vector gives the speed (compare the length with the radial axis, from the origin) • Direction of the vector gives the Vector length direction of motion.. gives the speed

Focus on the black line for this example…

Source: https://cameronnixonphotography.wordpress.com/research/the-storm-relative-hodograph/ Geostrophic winds (Vg) are a function of gravity/the Coriolis force and the gradient in Thermal Wind height of a pressure level

Thermal wind • is not a wind, it is a wind shear • is the difference in geostrophic wind between two levels in the Substituted atmosphere geostrophic Thermal Wind (V ) = Difference between • relates the vertical geostrophic T wind equation wind shear (change in geostrophic geostrophic winds (VG) at two levels wind speed and direction with height) above a point between two levels, to the mean horizontal temperature gradient in the layer between the two levels Thermal winds (Vt) are a function of gravity/the Coriolis force and the gradient in thickness of a pressure level Thermal Wind

The geostrophic wind at 50 kPa (G ) Geostrophic winds blow parallel to 2 the pressure contours has veered, turning clockwise. Thermal winds ‘blow’ parallel to the thickness contours In this example: • There is a thickness (directly related to layer temperature) The geostrophic The thermal wind (M ) gradient (warming) from left to TH wind at 100kPa (G is the vector drawn to 1) right is blowing from connect G to G • The thermal wind is parallel to this 1 2 right to left gradient, with low thickness (cold air) on the left • Subtracting the two wind vectors (G2 – G1) produces the thermal wind vector

Vector Subtraction Source: Stull, R (2017) Warm Air Advection (WAA) More stable with time Layer Stability With Cold Air Advection (CAA) Time Cold Air Advection (CAA) Less stable with time Warm Air Advection (WAA) Based on layering in the direction of the wind shear across a layer (backing/veering), you can determine how the stability of layers will change over time Layer (1000’s ft.) Wind Advection Warm Air Advection (WAA) above 0 – 3 Backing CAA Cold Air Advection (CAA) 3 – 7 Unidirectional -- becomes more stable with time 7 – 18 Veering WAA Cold Air Advection (CAA) above Warm Air Advection (WAA) becomes 18 - 19 Backing CAA less stable with time 20 - 23 Unidirectional --

Less Stable With Time

Not real data* Discussion Questions

In addition to the annotated hodograph, there are several questions to answer • Questions 2 has 14 parts (a – n), each asking for details derived from the hodograph Some questions can be answered on the hodograph plot • Please indicate in your write up that the answer is located on the plot if so

Assignment

This lab assignment is due at the start of next week’s lab (October 1st at 8:30 am) It is worth 4 % of the final course grade Includes the annotated Hodograph with: 1. Wind speed and direction at various heights 2. Frontal thermal wind vector 3. Additional annotations (can also be submitted with discussion questions) As well as a write-up of the remaining discussion questions (2 a – m)