# Seasonal Variations of Carbon Dioxide, Water Vapor and Energy Fluxes in Tropical Indian Mangroves
## 4 Results and Discussions
### Heat Fluxes and Energy Balance  
The maximum half-hourly measured net solar radiation (R\({}_{\rm n}\)) was nearly 700 W\(\cdot\) m\({}^{-2}\) during the summer season (April 2012 and March 2013) and 500 W\(\cdot\) m\({}^{-2}\) during the winters (November 2012 to January 2013). The partitioning of the net available energy into sensible heat flux (H) and latent heat flux (LE) was almost the same throughout the year. During the study period from April 2012 to March 2013, both H and LE showed a linear relationship with net radiation with values peaking during midday.  
The monthly diurnal average values of sensible heat flux (maximum of 240 W\(\cdot\) m\({}^{-2}\) during April 2012) and latent heat flux (maximum of 240 W\(\cdot\) m\({}^{-2}\) during October 2012) depicts that the net radiation was equally divided into both energy fluxes for most months of the year (Figure 9). During July 2012 to November 2012, energy partitioning into latent heat flux was slightly higher than the sensible heat flux. This is largely due to the availability of water due to rain events, which triggered evapotranspiration at the study site.  
Closure of the surface energy balance provides insight into the performance of the eddy covariance measurement system [(11; 42)]. For each half-hour period, the total net radiation (R\({}_{\rm n}\)) should be approximately equal to the sum of the energy distributed between the LE, H, and soil heat flux  
Figure 8: Monthly mean diurnal variations of half-hourly H\({}_{2}\)O flux during April 2012 to March 2013. The error bars show one standard deviation of the diurnal average fluxes during the respective months.  
Figure 9: Annual variation of monthly mean diurnal variation of sensible heat and latent heat fluxes.  
(G) and canopy heat storage (S). Since the canopy heat storage (S) is expected to be small in short canopies with minimal biomass [42], the surface energy balance at the surface can be expressed as:  
\[R_{n}-G\,=\,H\,+\,LE\]  
Figure 10 shows the energy closure of the Sundarbans study area during the day from April 2012 to March 2013 with measured half-hourly flux values. Figure 10 also depicts that the slope of the regression (\(m=0.78\)) was less than one and the intercept (\(c=18.7\)) was slightly greater than zero with an \(R^{2}=0.74\). The surface energy balance of about 78% of the available energy is accounted for by the 30-min fluxes in the present mangrove ecosystem. Although the energy balance closure is not perfect, it is the typical range reported at other flux sites. [PERSON] _et al._, 2002, used 22 FLUXNET sites of different vegetation heights and compositions and reported the ranges of slope, intercept and \(R^{2}\) to be in between 0.53 and 0.99, \(-\)32.9 and 36.9 W\(\cdot\)m\({}^{-2}\), and 0.64 and 0.36, respectively. Other long-term eddy covariance studies also indicate that the measurements do not show a closure of surface energy balance, although this discrepancy is not well understood [42; 43; 44]. It is also considered that the imbalance may be due to the sensor accuracy, data processing and under-estimations of the advections due to homogenous terrain.