Download ...Sunshine Data Recorded at RERC , Dhaka University Campus, Dhaka, Bangladesh  ( Duration January 1988- December 1997)  ( 416 Kb)

Objectives of the study :  

If-

• measured values of sunshine duration are not available

• the measurements are unhappy for a few locations

• other climatological parameters like Cloud cover and Rainfall data may be used to estimate sunshine duration

Measurement of Sunshine duration, Cloud cover and Rainfall

• Bangladesh Meteorological Department (BMD) has 31 and

• Bangladesh Rice Research Institute (BRRI) has 5 Sunshine

• duration measuring stations

• Campbell-Stokes sunshine recorders have been using there

• BMD has been also collecting Cloud cover data in unit Octa

• Bangladesh Water Development Board (BWDB) has approx.

• 269 rainfall stations

Data collection

·         Data of Sunshine duration have been collected for period 1981 to

·         2001 from BMD and 1982 to 2002 from BRRI

·         Data of Cloud cover have been collected for 1981 to 2001 from

·         BMD For 56 stations rainfall data has been collected from BWDB 

Estimation of Sunshine duration

·         From Cloud cover

·         From cloud cover amount

·         From the state of the sky

·         From rainfall data

Screening of Sunshine duration and Cloud cover data

Figure 1: Variation of sunshine duration with  months

Variation of Sunshine duration with years

Figure 2:Variation of sunshine duration with years

Variation of sunshine duration and cloud cover with years both in a graph

 Figure 3: Variation of sunshine duration and cloud cover both in a graph Cloud cover is a specifier of sunshine duration. Their variation should be correlated Top graph of Figure 3, shows sunshine duration and cloud cover data are in reasonable agreement for all years

 Bottom graph below of Figure 3 does not show a good agreement between sunshine duration and cloud cover data for all years  

Satisfactory stations: 

• 20 stations of BMD have been found  satisfactory

• 6 stations of BMD have not been found satisfactory

• 5 stations of BMD are not quite satisfactory

Estimation of sunshine duration from cloud cover 

Method 1: using cloud cover amount 

A correlation between relative sunshine duration and cloud cover amount has been found such

 Regression parameters and errors: 

 The rms errors 0.45 hours/day

 Method 2: using the state of the sky :

Based on the work of Barbaro et al, the correlation employed is

 Where, is the total number of days in the month under consideration

The climatological parameters and errors

The rms errors 0.3 hours/day

Selection of method

• In method 1, estimated values have been found with a maximum deviation of 1 hour for different months

• In method 2, the errors are low

• Method 2 has been selected to determine sunshine duration

• The measured and estimated values do not agree well for 5 stations, for these average  of measured and estimated values have been taken

Methodology

 of estimation of Sunshine duration

 from rainfall amount:

• Correlation between relative sunshine duration and rainfall amount has been developed such

• Depending on annual rainfall amount, regression parameters of nearest Met stations have been chosen

• Average has been taken for stations, which rainfall are almost same for more than one Met station

Regression parameters and errors

Consideration of foggy days:

Fog has a small influence on sunshine duration

·         In Bangladesh a number of foggy days can be seen in January. In  another months number of foggy days are less.

·         For January fog factors are necessary to get the nearest value of the measured one. Statistically for another months no need for fog factor.

·         It has been chosen for the main Met stations and then implemented for the others. Fog factor of 0.85 to 1.00 has been introduced.

Preparation of Maps:

•Global, Diffuse and direct radiation values for different locations have been estimated from the measured and estimated values of sunshine duration

•The values have been plotted on the map of Bangladesh  to get a detail map of radiation

Turbidity parameters

The presence of aerosols makes the atmosphere turbid and the determination of turbidity gives the property of the atmosphere in the presence of aerosols

• Determination of turbidity parameters are going on

Table: Variation of Linke turbidity coefficient over the year

Period   2002                                         Period   1990-97

Month               TLK      sd         TLI        sd         TLK      sd

Jan                   3.78      0.43      3.50      0.36      3.66      0.37

Feb                   3.61      0.10      3.16      0.12      3.85      0.15

Mar                   3.77      0.27      3.22      0.26      4.83      0.26

Apr                   6.07      0.25      5.54      0.28      4.25      0.15

May                  6.32      0.39      5.77      0.34      4.54      0.45

Jun                   6.03      0.03      5.40      0.03      4.03      0.74

Jul                    -----       -----       -----       -----       -----       -----

Aug                  4.72      0.13      4.04      0.18      -----       -----

Sep                  4.78      0.43      4.17      0.16      4.06      0.23

Oct                   3.38      0.14      2.90      0.18      3.46      0.35

Nov                   3.34      0.67      2.94      0.68      3.54      0.25

Dec                  3.45      0.09      3.15      0.11      3.62      0.21

Annual avg.       0.45     4.48      0.27      3.98      0.25      3.98