Analysis of Changes on Moisture Sources Contributions for Arctic Region in a Future Climate Scenario Using GFDL / CM 3 Model

The IPCC Fifth Assessment Report suggests that the projected increase in the global temperature in future scenarios could cause different impacts in different regions of the world. For the Polar Regions the global models are being adapted to measure these changes, but the preliminary results indicate large heating for the Arctic region. The changes on Arctic region are not a problem just for a future climate: the Arctic amplification, the decrease on Arctic sea ice extent and on snow cover extent is a present concern for climatologists. Studies suggest a link between Arctic changes and mid-latitude weather, as the changes on Arctic Region where observed accompanied by changes in other regions of the world, especially in the Northern Hemisphere mid-latitude. Some mechanisms are proposed to explain this link, and one of then is related to changes in the atmospheric moisture transport from middle latitudes. Recent studies have shown that the Mediterranean Sea, North Atlantic Ocean and North Pacific Ocean appear as the main regions that contribute as moisture sources to the Arctic Region. The objective of this work is to use the output of GFDL/CM3 Model for 2046–2075 and 2070–2099 periods to identify the regions of the main change on moisture sources that contributes to the Arctic Region in a future scenario (RCP4.5) compared to a present climate (1980–2005). For both future periods analysed, the results suggest that the contribution for Arctic moisture by the regions located on North Atlantic Ocean, North Africa and Middle East enhanced. This may indicate an increase in moisture transport from mid-latitude to Arctic that could lead to several changes in Arctic climate: warming, decrease on sea ice extent and on snow cover.


Introduction
Observational and modeling studies indicate that the water cycle is affected by changes in world temperature, in this way, is expected that in a warmer planet there will be important changes on water cycle [1].The Intergovernmental Panel on Climate Change (IPCC) on its last report (AR5) suggests that different regions of the world will present different changes, but in a general way these are alarming in relation to a possible increase on temperature, that can cause an increase in the number of extreme events (droughts, heavy rainfall events, warmer days and nights, heat waves, tornadoes, hurricanes).In particular, the Arctic Region is one to suffer the biggest expected impacts, showing changes never seen in the past decades [2].
The changes on Arctic climate is a concern, where extreme temperatures were registered on this century with an increase two times faster than the global average (Arctic amplification) [3].Associated to this warming, it was also observed a decrease on Arctic sea ice extent (the largest declined rate occurred in September: 12,4% per decade since 1979) [4]; and on snow cover extent (loss rate: 53% from 1959 to 2000) [5].
At the same time that these changes where observed on the Arctic, other regions of the world, especially in the Northern Hemisphere mid-latitudes, showed the occurrence of extreme heat and rainfall events [3].These facts suggest a possible link between Arctic change and mid-latitude weather.Some dynamical changes where proposed by [3] to explain this link: changes in storm tracks, weakeaning of the jet stream, and changes on configuration of the planetary waves [3].
The interpretation of the most significant observed changes in the Arctic can be related to changes in the atmospheric moisture (increased transport from middle latitudes) [6].[7] stressed that the study of the behavior of source and sink moisture regions allows the investigatigation on how occurs the water cycle around the world.In this way, [8] used a Lagrangian analysis to determine that Mediterranean Sea, North Atlantic Ocean and North Pacific Ocean appear as the main sources moisture regions to the Arctic.Besides, a connection between the increase in evaporation over these source regions and Arctic ice melting where founded.
In a study using 22 global circulation models from the Climate Model Intercomparison Project Phase 5 (CIMP5), [9] investigate projected changes on global atmospheric water vapor transport for future scenarios, finding an increase by 30%-40% over the storm tracks regions located on North Pacific and North Atlantic, and in the Equatorial Pacific Ocean.In this way, changes on regions that contributes as moisture sources to the Arctic could contribute to an intensification to the Arctic amplification, decrease on Arctic sea ice and on snow cover extent.
The objective of this work is to better understand how changes in the moisture on the regions of Mediterranean Sea, North Atlantic Ocean and North Pacific Ocean affect the moisture supply in the Arctic region.To perform these analysis we used the output of GFDL/CM3 Model for two future periods (2046-2075 and 2070-2099) considering the scenario RCP4.5, and compared to the present climate .

Experiments
In the study of [8] were computed the contribution of each moisture source to Arctic precipitation through the series of − < 0 using the Lagrangian Dispersion Particle Model FLEXPART (for more details see [8,10]).These series (hereafter Ps) where provided by these authors for the period 1980-2012.In this work, we only analyse the North Atlantic Ocean region (hereafter NAO) for October-March 1980-2005 (as in Gimeno et al., 2015) named present period.Monthly vertical integrated moisture fluxes in zonal and meridional directions were calculated as in [9] using ERA Interim data [11] for the present period; and the GFDL/CM3 model [12] for the present and two future periods with RC4.5 scenario: 2046-2075 (hereafter fut1) and 2070-2099 (hereafter fut2).
We performed linear correlations (r) between Ps and VIMF in zonal (VIMFz) and meridional (VIMFm) directions using Era Interim and GFDL/CM3 for the present period.The analysis of the regions of significant correlations (90% level) between the source (NAO) and the sink (Arctic) can provide us a better understanding about the moisture path between both.The analysis of r signal is important because > 0 indicate that an enhacend (decrease) on VIMF is associated to a enhanced (decrease) on Ps; and < 0 indicate that an enhacend (decrease) on VIMF is associated to a decrease (enhanced) on Ps.
A spatial mean of VIMFz and VIMFm in these regions were calculated for the present and futures periods, and the comparison of these data can show how are the changes on moisture path.

Results
The spatial pattern of VIMFz (Figure 1) and VIMFm (Figure 2) is well represented by the model when compared to Era Interim reanalysis in the historical period (Figure 2a,b).Comparing the two future periods (Figure 2c,d), the patterns are similar and intensity do not demonstrante any significant change.For the comparison of present and future periods one can see that the pattern is similar but the intensity is modified, suggesting possible changes on global atmospheric water vapor transport in a future scenario (as founded by [9]).The linear significant correlation (figures not shown) provide us four regions to analyse (Figure 3): two in zonal direction (Z1:orange and Z2: purple), and two in meridional direction (M1: blue and M2: red).The value of r is also indicated in Figure 3.The M1 region comprises the portion of the North Atlantic closed to Europe coast and = 0,29; the M2 region comprises the western portion of Europe and East Asia, with = −0,30; the Z1 region comprises North Africa and = −0,32; the Z2 region includes the North Atlantic Ocean on the east coast of North America , and = 0,29.
For each region (Z1, Z2, M1 and M2) the mean value for VIMFz and VIMFm for the present period using Era Interim and GFDL/CM3 Model and for the future periods are showed on

Discussion
The analysis for each region is performed analising the signal and the behavior of VIMF in the future period compared to the present period (increase or decrease) where these results are displaced in Table 2.For M1 region the correlation is positive and there is an increase in VIMFm for the two future periods in relation to the present; for M2 region the correlation is negative and the data show a decrease in VIMFm for the two future periods in relation to the present; for Z1 region the correlation is negative and there is a decrease in VIMFz for future periods; and for Z2 region the correlation is positive and VIMFz decrease for FUT1 and increase for FUT2.The regions where the VIMF value increases (decreases) in the future and the correlation is positive (negative) indicates that the moisture source has a higher contribution to the sink area.The regions where the VIMF value increases (decreases) in the future and the correlation is negative (positive) suggests that the moisture source contributes less to the sink area.
In this way, for all analysed regions and for both future periods (except for Z2) the GFDL/CM3 model shows a greater contribution of the regions to the moisture sources of the Arctic.This may indicate an increase in moisture transport and as we have previously cited, a decrease of the ice.
These analyses were performed considering the NAO source region, it is intended to also expand to North Pacifi Ocean (NPO) and Mediterraneo (MED).Following the work of Lavers et.al (2015) several CMIP5 models will also be analysed .

Conclusions
In this work we investigate the behavior of the moisture source region for the Arctic, located on the North Atlantic Ocean, considering a future scenario (RCP4.5)for two different periods: 2046-2075 and 2070-2099.For these analysis we used − < 0 series for Arctic sink region (that shows the contribution of the moisture source regions) (provided by [8]) and vertical integrated moisture fields on meridional and zonal directions to performe linear correlations.The regions in the path between the source and sink that shows best correlations provide locations to investigate changes in moisture fluxes in a future scenario.The vertical integrated moisture fluxes for future scenarios using the GFDL/CM3 model were usuful to better understand the expected changes in the climate.
For both future periods analysed, the results suggest that the regions located over North Atlantic Ocean, North Africa and Middle East, in the path between the moisture source (NAO) and the sink (Artic), occurs an increase on his contribuition for the Arctic moisture.These results may indicate an increase on moisture transport from mid-latitude to Arctic, that could lead to a temperature rise and significant changes (decrease) on ice extent and snow cover.

Figure 1 .
Figure 1.Vertical Integrated Moisture Fluxes (in . . ) on zonal direction for (a) Era Interim in the present period; (b) GFDL/CM3 Model in the present period; (c) GFDL/CM3 in the fut1 period; (d) GFDL/CM3 Model in the fut2 period.

Figure 3 .
Figure 3. Selected regions (M1, M2, Z1 and Z2) with a significant correlation ( ) between Ps series and VIMFz and VIMFm fields for NAO source region; and values for each region.

Table 1 .
Mean values for VIMFz and VIMFm (depending on the case) for selected regions for best correlations for NAO source.

Table 2 .
Summary for the results founded in these analysis: signal, behavior of VIMF in the future compared to the present period (increase or decrease), and conclusion for the source region contribuition to the Arctic moisture.