Interannual Variability of Energy Flux in Atmospheric Instability Conditions at Pantanal of Mato Grosso-Brazil

doi:10.4236/acs.2012.24046

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Atmospheric and Climate Sciences, 2012, 2, 518-524

http://dx.doi.org/10.4236/acs.2012.24046 Published Online October 2012 (http://www.SciRP.org/journal/acs)

Interannual Variability of Energy Flux in Atmospheric

Instability Conditions at Pantanal of Mato Grosso-Brazil

Leone Francisco Amorim Curado, José de Souza Nogueira, Luciana Sanches,

Marcelo Sacardis Biudes, Thiago Rangel Rodrigues

Programa de Pós-Graduação em Física Ambiental-UFMT, Brazil

Email: [email protected]

Received July 25, 2012; revised August 27, 2012; accepted September 7, 2012

ABSTRACT

The energy balance partitions in wetlands have gained notoriety due to the dynamics and importance of these areas for

regional and local climate. Thus, the study was conducted about seasonal and interannual behavior energy fluxes, as

well as the influences of the conditions of atmospheric stability and instability. The results showed highest fluxes

happened in instability atmospheric conditions. The fluxes of latent and sensible heat showed seasonal variation,

indicating that the water availability in the atmosphere has influence on the site energy partition, but the interannual

patterns remained similar during the two years of study.

Keywords: Latent Heat; Sensible Heat; Energy Partition; Wetlands

1. Introduction

The flood pulse is considered the driving force of the

Pantanal and the intensification of the season of dry and

wet seasons are the result of multi-annual fluctuations in

water level that influence the limnological seasonal char-

acteristics, ecological and biological [1]. October months

are the rains begin and it finish between February and

May, July and August are characterized as dry months in

this region, often causing hidric stress to the plants [2].

Vochysiadivergens is considered an invasive species

in Pantanal having a good adapting in flood area. This

species incursion in the Pantanal happened in the early

70 s, after the end of an intense and multi-annual period

of dry [3]. In not flooded areas the presence of Vochy-

siadivergens is rare or absent, but present a better devel-

opment in newly sedimented areas along rivers [4]. In

wetlands, there is no problem with this species, but when

it reaches the highest parts of Pantanal and advancing

toward fields forming forests, it becomes a problem, be-

cause it occupies Pasture areas [5].

The apparent cause of the spread of the species in the

region may be related to the alternation of major floods

and droughts that occur in the Pantanal and also by de-

forestation caused by livestock farmers in the region,

increasing the area available for the plant to establish.

These factors can cause shrinkage of native vegetation

and increases in populations of this species, giving the

vegetation an irregular character in time and space than

may lead to short and medium term changes in Pantanal

region climate [3].

The flux of latent and sensible heat can be obtained by

micrometeorological methods, direct and indirect (esti-

mated), the last one having the advantage of not altering

the environment. For direct measurement methods has

the eddy covariance system, which takes into considera-

tion the fluctuation of the concentration of water vapor,

temperature and fluctuation of wind speed to calculate-

ing the flux and latent heat sensitive respectively [6,7].

The advantage of using direct measures is that small fluc-

tuations in very low intervals of time are obtained, the

disadvantage is the value for the acquisition of the equip-

ment.

The LE and H quantification by Bowen ratio method

have been widely used in the last decade, for determining

the energy balance in many studies about the energy dy-

namics of forest and the management availability of wa-

ter for certain crops by evapo transpiration estimated by

the latent heat flux [8-12].

The atmospheric stability can be defined as a condition

in which atmospheric air upward movements are absent

or permanently inhibited, whereas the condition of insta-

bility is defined as the atmospheric state in which prevail

the vertical movements. The characterization of these

atmospheric conditions is realized according to the tem-

perature distribution of air, i.e., an air layer is considered

stable or unstable depending on the value of vertical

temperature gradient observed in the layer. It should also

consider the situation in which the vertical temperature

L. F. A. CURADO ET AL. 519

gradient in the atmospheric layer coincides with the rate

dry adiabatic. In such condition, the air parcel to ascend

or descend will always have the same temperature of the

medium that it surrounds, without resistance nor further-

ing of the vertical movement of the air layer, featuring

neutral atmospheric condition [13].

The objective of this work was to study the seasonal

behavior of the energy fluxes for stability and instability

atmospheric conditions in an area of Vochysiadivergens

at Pantanal of Mato Grosso-Brazil.

2. Materials and Methods

2.1. Study Area

The study was conducted in an area located in the Private

Reserve of Natural Heritage—PRNH SESC—Pantanal,

in Barão de Melgaço city—MT, distant 160 km from

Cuiabá—MT where a micrometeorological tower was

installed at 32 m in height (16˚39′50″S, 56˚47′50″W)

and120m level. This area has a mono-dominate vegeta-

tion of Cambará (Vochysiadivergens, Phol), Known lo-

cally as cambarazal, with canopy heights ranging from

28 to 30 m (Figure 1).

2.2. Measurements

The net radiation was measured for one net radiometer

(Kipp&Zonen Delft, Inc., Holland), and the heat flux in

soil was measured by two fluxímeters (HFT-3.1, REBS,

Inc., Seattle, Washington) installed at 0.05 m e 0.25 m

depth. The gradients of temperature and humidity were

estimated by two thermohygrometer (HMP 45 C, Vaisala,

Inc., Helsinki, Finland) installed at 33.7 m e 37.7 m

height in micrometeorological tower.

2.3. Methods

Atmospheric stability (ξ) was calculated using two meth-

ods (Equations (1) and (2)).

0,4

cTu



 (1)

where, g is the gravitational acceleration (9.8 ms–1), Tk is

the air temperature (K), u* is the velocity of air friction

(ms–1), ρ is the air density (1.292 kg·m–3), cp is the

specific heat of the humid air (1013Jkg–1·C–1), H is the

sensible heat flux where z is the height was measured

wind speed.

Figure 1. Localization of the micrometeorological tower in the RPPN-SESC Pantanal in MatoGrosso-Brazil.

L. F. A. CURADO ET AL.

520

The sensible (H) and latent (LE) heat fluxes were

calculated according to Equations (2) and (3), respec-

tively.













v



(2)

















(3)

Where Rn is net radiation, G is the soil heat flux and β

is the Bowen ratio, given by:









(4)

where Δt is difference temperature between two levels

3. Results and Discussion

ondition and ux

Tab ric

as noted that the highest

es of seasonal latent heat in the

rai

energy into latent and sen-

ric conditions

Table 1. showsthe daily average values of atmospheric cond-

(˚C), the difference Δe pressure of water vapor between

two levels (kPa) and the constant γ psychometric (0.0626

kPaC–1).

3.1. Seasonality of Weather C

Patterns of Latent and Sensible Heat Fl

le 1 shows the daily average values of atmosphe

conditions (stability and instability) and the latent heat

and sensible in the study area.

According to Table 1, it w

lues of the latent heat and sensible occur with atmo-

spheric in stability, which is because in unstable cond-

itions conducive to turbulence that is the most favorable

condition for energy transferring and matter between

surface and atmosphere.

The daily average valu

ny season were higher than in the dry, which also

resulted in an increase in the sensible heat flux during the

dry period, indicating that the water content due to the

precipitation region is a factor determining the amount of

energy from the sun which is used to evaporate the water

and increased temperature.

This conversion of solar

ble heat is critical for the regulation of ecosystems.

According to [14], temperature and humidity conditions

within and above a forest are the result of transmission

and absorption of solar energy on the surface of the

canopy, its conversion into sensible and latent heat and

the allocation of light and heat in a forest.

The average daily values of atmosphe

owed that both stability and instability remained

approximately the same values in both periods (rainy and

dry) during the two years studied (2007 and 2008), which

indicates a weather regulation in the region of the study.

itions (stabilityand instability) and the latent heat and

sensible in the study area.

2007 2008

Wetseason Instability maximum −0.11 −0.22

Staity

LE—U stable

mi −

LE—able

H—Utable

H—able

Dryseason Instability

Staity

LE—U stable

mi −

LE—able

H—Utable

mi −

H—able

minimum −0.61 −0.60

mean −0.40 −0.39

bilmaximum 0.16 0.09

nimum −0.01 −0.01

mean 0.05 0.03

nmaximum 547.04 454.49

nimum 51.02 41.08

mean 306.42 280.57

Stmaximum 94.74 109.05

nimum −34.82 −21.6

mean 0.3 15.94

nsmaximum 111.54 107.94

nimum 9.72 −6.82

mean 59.73 61.48

Stmaximum 18.54 22.31

nimum −7.47 −3.36

mean 0.76 3.96

maximum −0.18 0.15

nimum −0.57 −0.62

mean −0.37 −0.36

bilmaximum 0.09 0.11

nimum −0,02 −0.01

mean 0.01 0.02

nmaximum 348.47 352.96

nimum −7.4 46.01

mean 234.02 216.03

Stmaximum 60.42 77.23

nimum −39.93 −37.91

mean 0.57 4.9

nsmaximum 118.83 149.26

nimum −1.41 7.76

mean 58.57 66.02

Stmaximum 15.68 23.06

nimum −15 −14.91

mean 0.33 0.7

3.2. Inter-Annual Variabil Wea

Conditions and Patterns of Latent and

The t the

eneron average

ity ofther

Sensible Heat in the Rainy Season

values in Table 1an d Figure 2 indicate tha

gy converted into latent heat flux was

higher than the energy converted into heat sensitive

within two years of study during the rainy season, except

on condition of stability of the year 2007, which indicates

that the amount of water present in the atmosphere is a

L. F. A. CURADO ET AL. 521

regulating agent of the ecosystem in question, this result

was found by [2].

Another important factor is that in analyzing inter-an-

nual patterns in atmospheric conditions (stability and

her

Conditions and Patterns of Latent and

Acco y

perioy most of the

stability) were between one year and one which also

occurred with the latent heat and sensible, who have

followed these conditions, with higher instability values

than the stability in the two years of study, thus

indicating that during the wet season of 2007 and 2008

standards in these variables kept the same.

3.3. Inter-Annual Variability of Weat

Sensible Heat in the Dry Season

rding to Figure 3, it was noted that as in the rain

d between the study period, in the dr

available energy to the ecosystem was converted into

latent heat, showing that even in periods with little or no

precipitation the evaporative requirement is relatively

high compared with the sensible heat flux, demonstrating

that the latent heat flux is the main component of the

energy balance in this region.

The same to the rainy season, the highest values of

latent heat flux and sensible culminated with the

conditions of atmospheric instability, which as already

mentioned in Section 3.1, this condition favors the turbu-

lence that promotes the energy transfer between the

surface and atmosphere through the fluxes of latent and

sensible.

Another important factor is the greater variability of

the data sensible and latent heat flux in the dry season

than in rainy season in both years studied, this is caused

Wet season - 2008

Wet season-2007

Atmosph erics conditions

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8 Unstability

Stability

Latent heat flux (W .m

-2

)

LE - Unstable

LE - Stable

-100

100

200

300

400

500

600

Days

0 102030405060708090

Sensible heat flux (W.m

-2

)

-20

100

120

140 H - Unstable

H - Stable

0 102030405060708090

Days

Figure 2. Daily average values of conditions atmospheric stability, atmospheric instability and flux of latent and sensible heat

during the wet season in the years 2007 and 2008.

L. F. A. CURADO ET AL.

522

Dry season- 2007Dry season - 2008

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

0,8

Unstability

Stability

Atmospherics conditions

Latent heat flux (W.m

-2

)

LE - Unstable

LE -Stable

-100

100

200

300

400

Days

0 102030405060708090

Days

0 102030405060708090

Sensible heat flux (W .m

-2

)

H - Unstable

-50

100

150 H - Stable

Figure 3. Daily average values of conditions atmospheric stability, atmospheric instability and flux of latent and sensible heat

during the dry season in the years 2007 and 2008.

mosphere

, drier air and lower radiation

[17].

reported in the Cerrado and Amazon transition forest-

hest values of energy flow by favoring the

between the surface and atmosphere

by the fact that there is greater variation in temperature in

e region due to low water content in the at

Lower values of LE, during the dry period, were also

and also for this period include the winter season than in

the southern hemisphere occurs between June and Sep-

tember, which causes abrupt changes in temperature, thus

causing a greater variability in the energy flux data. This

greater variability in temperature data during the dry

period is described in [15].

Lower values of LE during the dry period can be expl-

ained by lower temperatures

(winter solstice), and is a limiting feature of this water at

this station canopy. During the dry season, there is a

decline in water content in soil and can limit evaporation

and water availability for plant root surface [16]. How-

ever, higher values of evapotranspiration in the wet season

were related to increased rainfall and flood water depth

savanna in the Midwest, while in tropical rain forests

located in Manaus, Santarem and Rondonia citywere

reported lower values of evapotranspiration during the

wet season [18,19].

Thus, the partition of energy in the Pantanal regions is

strongly influenced by water availability in soil and

atmosphere and the conditions of instability and stability

atmospheric.

4. Conclusions

Latent and sensible heat flux was influenced by weather

conditions in the region, and the condition of instability

caused the hig

transport of energy

through turbulence.

L. F. A. CURADO ET AL. 523

The most of available energy were converted into

latent heat in the two years of study, showing that the

water content is a regulatory agency in the region.

The variables studied (instability, stability, latent heat

and sensible heat) showed similar patterns for the same

ntífico e Tecnológico (CNPq)

Amparo a Pesquisa do

MAT) through the Support

anadian Special Publication of Fisheries and Aquatic

Sciences, Otta

riod, the interannual analysis.

Water availability and season influenced the parti-

tioning of energy of site.

5. Acknowledgements

The authors thank Coordenação de Aperfeiçoamen to de

Pessoal do Ensino Superior(CAPES), Conselho Nacional

de Desenvolvimento Cie

for Scholarship and Fundo de

tado de Mato Grosso (FAPE

Es-

Program for Centers of Excellence (PRONEX) for finan-

cial support to the research project process No. 823971/

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