SNOW HYDROLOGY (GEOG 4321): HOMEWORK ASSIGNMENT 4

Instuctor: Mark Williams
Telephone: 492-8830

Homework 4

• Assigned 14 May.
• Due 16 May before classs.
• There are 30 possible points, each question is worth 6 points.
• SHOW ALL YOUR WORK.
• WRITE NEATLY and LEGIBLY.
• WRITE THE QUESTION AT THE START OF EACH ANSWER.

1. Mountain snowpacks are best characterized by digging snowpits in order to measure changes in physical properties of the snowpack (temp, density, stratigraphy...) with depth. For the next two questions, you will compare data collected from pits 006 and T3E on 14 March 1995. Pit 006 is a snow pit at a natural site on the saddle of Niwot Ridge. Pit T3E is behind a snowfence, only 50 m from pit 006. The snowfence is part of a long-term experiment to look at the effects of increased snow deposition on the biology and chemistry of an alpine tundra ecosystem. Please show all of the work for your answers. To find the data, go to the NWT LTER web page, select Data, then Hydrology and Geomorphology, then Snow Cover Profiles: Raw Data.
   • Calculate the mean density for each of the pits.
   • Calculate the mean temperature for each of the pits.
   • Calculate the total snow water equivalence for each of the pits.
   • note: the first and last rows of data for each snowpit contain only the temperature at the snow/soil interface and at the snow surface respectively.
2. For the same snowpits (006 and T3E on 14 March 1995), graph a temperature profile and graph a density profile. The x-axis is either temperature or density, increasing from left to right. The y-axis is snow depth in meters, with 0 (the soil) at the bottom of the y-axis and the top of the y-axis is the top of the snowpack. Density is the column "measured weight"; units are grams/1000ml, which is the same as kg/m3. Temperature is the column "measured temperature".
   • Graph temperature from the two pits on the same graph.
   • Graph density from the two pits together on another graph.
   • In ten sentences or less, explain why the two pits have different density and temperature values.
3. Wind during snow events generally causes precipitation gauges to undercollect the "true" snowfall amount. The Niwot Ridge saddle area during the winter months is characterized by average wind speeds of about 10-13 m/s. Further up Niwot Ridge, the D1 meteorological site has much lower wind speeds. Compare the annual precipitation amounts from Sdl and D1 to see if they do in fact collect significantly different amounts of annual precipitation.

   Year	Saddle	D1
   (year)	(mm)	(mm)
   ----	----	----
   1986	1117	0908
   1987	1790	1271
   1988	1497	1055
   1989	1827	1074
   1990	1877	1037
   1991	1269	1213
   1992	1985	1502
   1993	1544	1159
   1994	2683	1568
   1995	2955	1231
   

   • Graph an XY scatter plot of Saddle (dependent variable) versus D1 (independent) annual precipitation.
   • Regress Sdl ppt on D1 ppt using a linear relationship. Include the line equation and r2 values on the graph. Is there a significant relationship between precipitation measurements at the two sites on an annual timescale?
   • Test to see if annual Sdl ppt is significantly different than D1 ppt using a paired t-test (the default on Excel)
4. Following is a small data set on wind speed and catch ratio of snowfall from Niwot Ridge. Graph wind speed (x axis) versus catch ratio on the y-axis. Explain these results in 5 sentences or less.

   Wind	Catch
   Speed	Ratio
   (m/s)	(fraction)
   ----	----
   1.6     1.00
   1.75    0.91
   2.5     0.59
   2.7     0.58
   8.2	1.23
   

5. The precipitation amount measured by a precipitation gauge can be adjusted for blowing snow using the following equations:
   

   	Pa = K * Pg
   		Pa = adjusted precipitation
   		Pg = gauge-measured precipitation
   		 K = 1/CR, adjustment factor for wind-induced error
   		CR = catch ratio of the gauge
   		CR = alter shield and snow = exp (0.0055-0.133Ws)
   		CR = no shield and snow = exp (-0.251-0.176Ws)
   		Ws = Wind speed (m/s) at gauge opening 
   		CR = HAS NO UNITS, SINCE WE ARE CALCULATING A RATIO
   		note: exp(x) = ex	
   
   	  
    Assume 50 mm of precipitation for the following questions:
   	  
    What is Pa for Ws = 0; alter shield and snow?
   	  
    What is Pa for Ws = 2; alter shield and snow?
   	  
    What is Pa for Ws = 10; alter shield and snow?
   	  
    What is Pa for Ws = 10;  no alter shield and snow?