College project - altitude equation

SeaFields · 05-08-2009, 11:11

Hi all,

I'm just finishing off a college project that has taken all of three years. It has been recommended by my external examiner in college that I modify my precipitation data with an altitude equation so as to better reflect my study area.

If there is anyone who has one off hand or could point to where I could get one online I would really appreciate it as I am against the clock to finish this.

Thanks

TheGreenGiant · 05-08-2009, 14:12

No problem

There is a few equations that you can use. I think what you are referring to is geopotential height. I'm going to give you what I have here in my book. Sorry if its a bit long but its just to explain what the equations are about.

1)Geopotential height is a vertical coordinate referenced to Earth's mean sea level — an adjustment to geometric height (elevation above mean sea level) using the variation of gravity with latitude and elevation. Thus it can be considered a "gravity-adjusted height." One usually speaks of the geopotential height of a certain pressure level, which would correspond to the geopotential height necessary to reach the given pressure. At an elevation of h, the geopotential is defined as:

where g(φ,z) is the acceleration due to gravity, φ is latitude, and z is the geometric elevation.
Thus, it is the gravitational potential energy per unit mass at that level. The geopotential height is

where g0= 9.8 m/s-2 which is the standard gravity at mean sea level.

Since it accounts for the variation of gravity, geopotential height simplifies the expression for hydrostatic balance. In terms of Z, (the hydrostatic balance for an incremental atmospheric column of cross sectional area dA and height dz): it reduces to dp=-pgdz =-pg0dZ

Hope this helps

SeaFields · 05-08-2009, 19:17

Thanks greengiant,

Really appreciate your reply.

TheGreenGiant · 05-08-2009, 19:30

No probs, best of luck with the project

M.T. Cranium · 07-08-2009, 07:28

Something else to keep in mind, if this would apply at all to your project, is that precipitation generally increases to a maximum about 1,000 metres above sea level on west-facing mountains, assuming that they rise higher than that. If you are looking at a region with mountains, in a mid-latitude temperate climate, then quite often the rainfall (including melted snow) will be 3-10 times as great at the 1,000 metre elevation facing west, as it would be on a valley floor or on relatively flat terrain to the west of the mountain range. And also, the average precip would be slightly greater on the east side of the mountain range at that altitude than further down, but those amounts would both be less than on the west side of the mountains.

This would reverse in the subtropics where precip moves from east to west on trade winds. And it would not apply in arid climates far removed from moisture sources or well to the north of the mid-latitudes.

05-08-2009, 11:11	#1
SeaFields Registered User Join Date: Dec 2008 Posts: 423 Adverts \| Friends	College project - altitude equation Hi all, I'm just finishing off a college project that has taken all of three years. It has been recommended by my external examiner in college that I modify my precipitation data with an altitude equation so as to better reflect my study area. If there is anyone who has one off hand or could point to where I could get one online I would really appreciate it as I am against the clock to finish this. Thanks

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

05-08-2009, 14:12	#2
TheGreenGiant Registered User Join Date: Jul 2008 Location: Trim, Co.Meath Posts: 260 Adverts \| Friends	No problem There is a few equations that you can use. I think what you are referring to is geopotential height. I'm going to give you what I have here in my book. Sorry if its a bit long but its just to explain what the equations are about. 1)Geopotential height is a vertical coordinate referenced to Earth's mean sea level — an adjustment to geometric height (elevation above mean sea level) using the variation of gravity with latitude and elevation. Thus it can be considered a "gravity-adjusted height." One usually speaks of the geopotential height of a certain pressure level, which would correspond to the geopotential height necessary to reach the given pressure. At an elevation of h, the geopotential is defined as: where g(φ,z) is the acceleration due to gravity, φ is latitude, and z is the geometric elevation. Thus, it is the gravitational potential energy per unit mass at that level. The geopotential height is where g0= 9.8 m/s-2 which is the standard gravity at mean sea level. Since it accounts for the variation of gravity, geopotential height simplifies the expression for hydrostatic balance. In terms of Z, (the hydrostatic balance for an incremental atmospheric column of cross sectional area dA and height dz): it reduces to dp=-pgdz =-pg0dZ Hope this helps

05-08-2009, 19:17	#3
SeaFields Registered User Join Date: Dec 2008 Posts: 423 Adverts \| Friends	Thanks greengiant, Really appreciate your reply.

05-08-2009, 19:30	#4
TheGreenGiant Registered User Join Date: Jul 2008 Location: Trim, Co.Meath Posts: 260 Adverts \| Friends	No probs, best of luck with the project

07-08-2009, 07:28	#5
M.T. Cranium Registered User Join Date: Apr 2007 Location: Canada Posts: 1,025 Adverts \| Friends	Something else to keep in mind, if this would apply at all to your project, is that precipitation generally increases to a maximum about 1,000 metres above sea level on west-facing mountains, assuming that they rise higher than that. If you are looking at a region with mountains, in a mid-latitude temperate climate, then quite often the rainfall (including melted snow) will be 3-10 times as great at the 1,000 metre elevation facing west, as it would be on a valley floor or on relatively flat terrain to the west of the mountain range. And also, the average precip would be slightly greater on the east side of the mountain range at that altitude than further down, but those amounts would both be less than on the west side of the mountains. This would reverse in the subtropics where precip moves from east to west on trade winds. And it would not apply in arid climates far removed from moisture sources or well to the north of the mid-latitudes.