SNOW HYDROLOGY (GEOG 4321): HOMEWORK ASSIGNMENT 3

Instuctor: Mark Williams
Telephone: 492-8830

Homework 3

• Assigned 14 May.
• Due 16 May before class.
• There are 30 possible points, questions are worth between 4 and 10 points.
• SHOW ALL YOUR WORK.
• WRITE NEATLY and LEGIBLY.
• WRITE THE QUESTION AT THE START OF EACH ANSWER.

1. Suppose you skied up to Niwot Ridge and drank all the liquid in your 1 liter water bottle, then tightly replaced the cap. Calculate the new volume of your water bottle upon returning to Boulder, using the Ideal Gas Law. Assume that at Niwot Ridge the air temperature was -10degC and atmospheric pressure was 0.5 atm; in Boulder the air temperature was +27degC and atmospheric pressure was 0.9 atm (4 points).
2. The Green Lakes Valley is located within the city of Boulder Watershed, consequently, it is an important source of water for the City of Boulder. Calculate mean SWE, density, and temperature for Green Lakes Valley, April 1996. To do so, use data from 10 snowpits located throughout the valley. Go to the NWT LTER web page, select Data, then Hydrology and Geomorphology, then Snow Cover Profiles: Snow Water Equivalence.
   • The ten snowpits located in Green Lakes Valley are: AVN, AVV, G3N, G3S, G3V, G4S, G4V, G5N, G5S, and G5V. Each of the ten pits was sampled on either 23 or 24 April, 1996. Calculate the mean, standard deviation, and standard error for snow depth,density, temperature and SWE at the ten pits.
   • Snowpit 006 is an "index" snowpit that we sample weekly with the hope that it represents the Niwot Ridge saddle and Green Lakes Valley. Compare the mean results from the ten Green Lakes Valley sites for snow depth, SWE, temperature and density to that of pit 006 on 25 April 1996. Are these values from pit 006 representative of the average Green Lakes Valley snowpack parameters you calculated from the ten snowpits above? Give your answer in five sentences or less (8 points total).
3. How well do SnoTel sites work for measuring SWE? Here we will compare manual SWE measurements made at snow courses to measurements made at automated SnoTel sites. Assume that SWE measured at snow courses is the "true" SWE measurement. At Wolf Creek pass , compare annual SWE measurements made in April from snow course data (independent variable) to SnoTel data (dependent variable) (10 points total) .
   • Regress SnoTel annual SWE values against snow course data.
     • Show graph with regression line.
     • what is the r-squared?
     • what is the slope of the regression line?
     • what is the y-intercept of the regression line?
     • is this a significant relationship between the SnoTel and snow course data?
   • Compare SnoTel and snow course annual SWE values using a paired-difference t-test.
     • What is the mean of the difference between the two methods?
     • What is the standard deviation of the difference between the two methods?
     • What is the t-statistic?
     • Is the SnoTel measurement of SWE significantly different than the snow course measurement of SWE at the 0.05 probability level?
4. 4. A Proposal has been made to replace all snow courses in the western US with SnoTel sites. Use the results from the statistical analyses in question 3 as well as your knowledge of the advantages and disadvantages of SnoTel and snow course measurement systems to answer the following questions (6 points) :
   • In terms of the accuracy of the data being collected what would the consequences of this move be? In other words are SnoTel sites a good substitute for snow courses in terms of both the magnitude of SWE measured at the site each year and the interannual trends in the SWE record?
   • What are some of the functional disadvantages of SnoTel sites as compared to snow courses?
5. What is the temperature range and supersaturation range where dendritic snow crystals are found (2 points) ? Answer is in the Avalanche Handbook.