Temporal Functions

Aggregation performed temporally along the timestamps for each cell location, producing a single grid. These functions are usually used with GROUP BY keyword and combined with other functions, such Avg_S and Render, to produce the result.

Avg_T

• Syntax: Avg_T(grid) returns the mean value of each cell location for a specified time resolution.
• Example:

/*Calculate the monthly mean land surface temperature(TSURF) for 2010 based on the hourly data. */
SELECT month, Avg_S(Avg_T(grid)), Render(Avg_T(grid)) FROM MST1NXMLD 
WHERE variable = "TSURF" AND year = 2010 
GROUP BY month ORDER BY month

Sum_T

• Syntax: Sum_T(grid) returns the sum of each cell for a specified time resolution.
• Example:

SELECT month,day, Max_S(Sum_T(grid)) FROM MST1NXMLD 
WHERE variable = "TSURF" AND year = 2010 AND month=5 GROUP BY day

Std_T

• Syntax: Std_T(grid) returns the standard deviation of each cell location for a specified time period. (Note: use StdSample_T(grid) for sample data).
• Example:

/*Calculate the standard deviation of the July precipitation(PRECCU) for each cell location from 1979 to 2015*/
SELECT Render(Std_T(grid)) FROM MATMNXINT
WHERE variable = "PRECCU" AND year BETWEEN 1979 and 2015 AND month = 7

Variance_T

• Syntax: Variance_T(grid) returns the variance of each cell location for a specified time period. (Note: use VarianceSample_T(grid) for sample data).
• Example:

/*Calculate the variance of the July precipitation(PRECCU) for each cell location from 1979 to 2015*/
SELECT Render(Variance_T(grid)) FROM MATMNXINT
WHERE variable = "PRECCU" AND year BETWEEN 1979 and 2015 AND month = 7

Corr_T

• Syntax: Corr_T(grid1,grid2) returns a correlation coefficient between grid1 and grid2 for cell location. Number of samples equals to then number of timestamps.
• Example: