Cven 3501 - the Bureau of Meteorology

 CVEN3501 - Assignment 1 2018

Question 1: Penman Monteith Evapotranspiration

Firstly, it must be noted that no data for January 2017 was available since the Bureau of Meteorology only displays data for the past 14 months. January 2018 data was used in its place, however, on 4th January 2018 data was missing for Sydney (station number 066062) and previous days were also missing data and hence a linear interpolation could not be undertaken. As a result, neighbouring station Sydney Airport AMO (station number 066037) was used for the entirety of this assignment.

Given the meteorological data for 4th January 2018 at Sydney Airport AMO, NSW using station 066037 (8.8km from Sydney) located at Latitude 33.95 S and Longitude 151.17 E, the following variables were calculated.

Mean Wind Speed:

Assumptions: Wind speed measurements made at 10m height and that the average wind speed is equal to the average of 9am and 3pm wind speeds.

𝑢10

= 𝑢9𝑎𝑚 + 𝑢3𝑝𝑚

2[pic 1]

ln (        2        )[pic 2]

𝑢2 = 𝑢10 _        0.0023

𝐼𝑛 (        10        )[pic 3]

0.0023

Mean Temperature:

Assumptions: Mean temperature is equal to the mean of the minimum and maximum temperatures observed.

𝑇𝑚𝑒𝑎𝑛

= 𝑇𝑚𝑎𝑥 + 𝑇𝑚𝑖𝑛

2[pic 4]

Saturated Vapour Pressure:

𝑒𝑠

= [𝑒(𝑇max) + 𝑒(𝑇min)]

2[pic 5]

𝑒 = 0.6108𝑒 (  17.27𝑇 )[pic 6]

237.3 + 𝑇

Actual Vapour Pressure:

Assumptions: Maximum and Minimum Relative Humidity is equal to the 9am and 3pm Relative Humidity measurements respectively.

𝑒𝑎

= (𝑒(𝑇min) 𝑥 𝑅𝐻max + 𝑒(𝑇max) 𝑥 𝑅𝐻𝑚𝑖𝑛)

2[pic 7]

Vapour Pressure Deficit:

𝑉𝑃𝐷 = (𝑒𝑠 − 𝑒𝑎)

Top of Atmosphere Radiation:

𝑅 = 118.1 𝑑

[pic 8]

[𝑤

𝑠𝑖𝑛(𝜑) 𝑠𝑖𝑛(𝛿) + 𝑐𝑜𝑠(𝜑) 𝑐𝑜𝑠(𝛿) 𝑠𝑖𝑛(𝑤 )]

𝑎        𝜋

𝑟        𝑠

𝜑𝑟𝑎𝑑

= 𝜋 180

𝑠

𝑥 𝜑[pic 9]

𝑑  = 1 + 0.033 𝑐𝑜𝑠 (2𝜋 +  𝐽 )[pic 10]

𝑟

𝛿 = 0.4903 𝑠𝑖𝑛 (2𝜋 𝑥        𝐽[pic 11]

365

365

− 1.405)

𝑊𝑠 = 𝑎𝑟𝑐𝑐𝑜𝑠[𝑡𝑎𝑛(𝜑) 𝑡𝑎𝑛(𝛿)]

Incoming Solar Radiation:

𝑛

𝑅𝑠 = 𝑅𝑎 (0.25 + 0.5 𝑁)[pic 12]