Compute Daily Mean Temperatures

Description

This tool computes daily mean temperatures from fixed hourly observations or from minimum and maximum temperatures. Modern hourly temperature data are required if the calculation of the daily mean temperature is from fixed hourly observations because the application of a correction term is needed to ensure compatibility with daily means calculated from minimum and maximum temperatures. HOB Tools will extrapolate all modern hourly temperature data to the top of the hour, solar time, and sunrise/sunset as required so comparisons between historical and modern records are as compatible as possible.

Notice of Temperature Assessment
HOB Tools will assess each fixed hourly or minimum and maximum temperature before a final daily mean temperature value is calculated and output. A warning message will be generated if any temperature value is ≥ 60°C or ≤ -40°C (e.g., Fig. 1). This allows for detection of temperature data that were incorrectly recorded (e.g., a value of 533 was entered instead of 53).

Figure 1. HOB Tools validates that all fixed hourly or minimum and maximum temperatures fall between -40°C and 60°C (inclusive), and generates a warning message if this condition is not met. The message details the temperature value that triggered the warning (purple box) and the exact date where it occurs (red box). It is then up to the user to decide if this potentially unrealistic temperature is acceptable. Select “No” to cancel the daily mean calculation process.

Temperature Format

Select the format of the daily temperature data. HOB Tools will compute daily means from hourly observations taken two or three times per day or from minimum and maximum observations. No adjustments based on analysis of modern hourly temperature data are required if "Minimum/Maximum" is selected, and the entire "Modern Input" area will be disabled.

Historical Input

Historical Temperature File
Select the historical temperature data to analyze by clicking on "Browse" and navigating to the proper file.

Historical Input Data Format
Year / Month / Day / Data

Each "/" is a tab (i.e., data should be tab-delimited). Missing Data should be denoted as "-99".

Temperature Units
Select the appropriate units for the historical data.

Historical Start Row
This input is the row number where the main data to be processed begin in the historical temperature file selected above. An example of how row numbers are entered is shown in Figure 2 located in the Running HOB Tools topic.

Data Columns
Enter the two or three columns of hourly temperature data in the historical dataset that will be compared to the modern data. An example of how column numbers are entered is shown in Figure 2 located in the Running HOB Tools topic. If "Hourly Three Times a Day" is selected under "Temperature Format" above, then all three input fields will be enabled. If one of the other formats is selected, then the last field will be disabled (i.e., only two input columns will be required). If these input data are fixed hourly temperatures (i.e., "Hourly Three Times a Day" or "Hourly Two Times a Day" is selected under "Temperature Format" above), then these columns must "match" with the selected hours in the “Modern Input” section as shown in Figure 2 (see also "Times to Compare" below).

Figure 2. Example of the Compute Daily Mean Temperatures tool. In this example, column number 4 in the historical dataset must correspond to 7 a.m. temperatures (red), column number 5 must correspond to 2 p.m. temperatures (purple), and column number 6 must correspond to 9 p.m. temperatures (green). The temperature format selected is “Hourly Three Times per Day”, so the “Second Daily Observation” under “Modern Input” is disabled. Neither sunrise nor sunset is a selected time, so the “Sunrise/Sunset File” and “Sunrise/Sunset Start Row” areas are disabled.

Modern Input

Modern Temperature File
Select the historical temperature data to analyze by clicking on "Browse" and navigating to the proper file.

Modern Input Data Format
Year / Month / Day / 1 a.m. / 2 a.m. / … / 11 p.m. / 12 a.m. / Maximum / Minimum

Each "/" is a tab (i.e., data should be tab-delimited). The “…” denoted above represents 3 a.m. through 10 p.m. Missing data should be denoted as “-99”.

Temperature Units
Select the proper temperature units for the modern data.

Modern Start Row
This input is the row number where the main data to be processed begin in the modern temperature file selected above. An example of how row numbers are entered is shown in Figure 2 located in the Running HOB Tools topic.

Top of the Hour Correction (minutes)
Enter the number of minutes prior to the top of the hour when observations were recorded in the modern temperature record. The default entry is 20 minutes, which was typical of many U.S. stations prior to the establishment of the Automated Surface Observing System (ASOS).

Solar Time Correction (minutes)
Enter the solar time correction in minutes. This allows HOB Tools to extrapolate standard time zones to solar time, so the proper daily mean correction can be calculated that takes into account solar time. If no solar time correction is required, a value of zero can be entered and no correction will be performed.

Second Daily Observation
If "Hourly Two Times a Day" is selected under "Temperature Format" above, then this field will be enabled. Select either an afternoon or an evening time that corresponds to the second fixed hourly observation. “Afternoon” is selected by default, but if “Evening” is selected, then the middle “Times to Compare” drop-down list box will be disabled (Fig. 2, circled in purple) and the list box on the right will be enabled (Fig. 2, circled in green).

Times to Compare
Select the times in the modern dataset that will be compared to the historical data. These selected hours must "match" with the column numbers entered in the “Historical Input” section as shown in Figure 2 (see also "Data Columns" above).

Sunrise/Sunset File
If sunrise and/or sunset is selected as one of the "Times to Compare" above, then the modern hourly temperature data will need to be extrapolated to sunrise and/or sunset. HOB Tools will then enable this input area, so the sunrise/sunset data file can be selected. Sunrise and sunset observations are available from the United States Naval Observatory website.

Sunrise/Sunset Input Data Format
If only sunrise is selected:

If only sunset is selected:

If both sunrise and sunset are selected:

Each "/" is a tab (i.e., data should be tab-delimited). Missing data should be denoted as “-99”. These data must start and end on the same day as the modern hourly temperature data.

Sunrise/Sunset Start Row
This input is the row number where the main data to be processed begin in the sunrise/sunset data file selected above. An example of how column numbers are entered is shown in Figure 2 located in the Running HOB Tools topic. This field will only be enabled if sunrise or sunset is selected as one of the "Times to Compare" above.

Output

Output File
Select the file where the new data will be stored.

Temperature Units
Select the appropriate units for the daily mean temperature data.

Output File Header
Information entered here will be output in the first line of the output file.