Dust emission and transport over Iraq associated with the summer Shamal winds

Question 1

summer Shamal wind

Answer 1

a quasi-permanent low- level northwesterly wind feature

Question 2

The Shamal exhibits an out-of-phase relationship between

Answer 2

• the surface wind and winds in the lower troposphere (typically 500 m above ground level)
• the maximum surface wind speeds being observed during the day while in altitude the maximum wind speeds are observed at night.

Question 3

The daytime near surface winds, at the origin of dust emission, are associated with

Answer 3

the downward transfer of momentum from the nocturnal low-level jet to the surface due to turbulent mixing after solar heating commences each day

Question 4

he dust load exhibits a large diurnal variability, with a daily minimum value of

Answer 4

1 Tg around 0600 UTC and a daily peak of 2.5 Tg or more around 1500 UTC

Question 5

he dust load exhibits a large diurnal variability, with a daily minimum value of 1 Tg around 0600 UTC and a daily peak of 2.5 Tg or more around 1500 UTC, and is dri- ven by

Answer 5

the diurnal cycle of the near surface wind speed.

Question 6

he daily dust load peak associated with the summer Shamal over Iraq is in the same order of magnitude as those derived from simulations down- stream of the

Answer 6

Bodélé depression in Chad, known to be the world’s largest dust source.

Question 7

The ‘‘Shamal” names

Answer 7

strong northwesterly winds blowing over Iraq and in the Persian Gulf area during

• the summer (June to September) and
  
  • blows almost continuously
• the winter (November to March)
  
  • occur two to three times per month between december and early march

Question 8

The summer Shamal blowing over Iraq and the Persian Gulf exhibits an out-of-phase relationship between the

Answer 8

surface wind and winds in the lower troposphere (typically 300–700 m above ground level, agl),

• the maximum surface wind speeds being observed during the day while,
• above, the maximum wind speeds are observed at night.
  
  • called nocturnal low level jet

Question 9

This Shamal-related LLJ is

Answer 9

primarily a thermal phenomenon which has recently been analyzed by using mesoscale simulations. They show that the mechanism appears to be secondary to the heating in forcing the LLJ.

Question 10

It has been well established in other parts of the world, notably Africa, that dust emissions over potential source areas are

Answer 10

related to surface wind speed maxima which occur in the hours after sunrise

Question 11

The phase shift in the diurnal cycle of the LLJ and surface winds is associated with

Answer 11

the downward transfer of momentum from the nocturnal LLJ to the surface due to turbulent mixing after solar heating commences each day

Question 12

Dust events associated with summer Shamal can reduce visibilities to

Answer 12

a few hundred meters

Question 13

the long-term drought and increased dust emission from Iraq largely contributes to the

Answer 13

recent increase in dust activity across the Arabian Peninsula.

Question 14

dust from Iraq associated with summer Shamal winds largely regulates

Answer 14

the interannual variability in summertime dust activity across Saudi Arabia

Question 15

dust storms are considered to be associated with visibility values of

Answer 15

3.5 km or less,

Question 16

For a given station, this threshold value on visibility allows to account for both strong dust events occurring near dust source regions in Iraq (characterized by visibilities

Answer 16

less than 1km

Question 17

or the same region. For a given station, this threshold value on visibility allows to account for both strong dust events occurring near dust source regions in Iraq (characterized by visibilities less than 1km, Middleton (1986b)) and events resulting from long-range transports (for which visibilities are

Answer 17

in the range 2–9 km

Question 18

In the case of propagating dust storms, the arrival of air- borne dust at a given site is generally associated with

Answer 18

a significant decrease in visibility and increase in wind speed

Question 19

he distribution of dust aerosols at regional scale (mobilization and transport) is described using three satellite products.

Answer 19

The Moderate Resolution Imaging Spectroradiometer (MODIS) fields of AOD are obtained from the MODIS/AQUA MYD08 (collection D3.051) daily level 3 products. Two AOD products at 550 nm are used: the AOD processed with deep blue algorithm (Hsu et al., 2004) over desert surfaces and the standard product processed over dark surfaces.

Question 20

The numerical simulation was made with the research model meso-NH (Lafore et al., 1998) version 4.7. The model domain (Fig. 2) had a grid mesh of

Answer 20

12 km and 70 vertical levels distant by 60 m close to the surface and distant by 600 m in the free tro- posphere.

Question 21

Operational ECMWF analyses were used as

Answer 21

lateral boundaries

Question 22

The simulation was run for 10 days starting at

Answer 22

0000 UTC 25 June.

Question 23

The model included

Answer 23

• a convective mass-flux scheme
• a mixed-phase bulk microphysical scheme
• a subgrid cloud cover and condensate content scheme
• a turbulence parameterization
• ORganic and Inorganic Log- normal Aerosols Model (ORILAM)
  
  • in which transport, dry and wet deposition, and radiative properties of the distribution of three dust particle size are parameterized
• the Rapid Radiative Transfer Model parameterization (that takes into account the radiative effect of dust and a dust scheme)
  
  • The later included the Dust Entrainment and Deposi- tion (DEAD) schemethat calculates dust fluxes from wind friction speeds

Question 24

The meso-NH model has been extensively validated over north and west Africa where

Answer 24

dust uplift associated with LLJ dynamics are observed on a regular basis all year round. It has been validated using many ‘‘aerosol related” datasets acquired from:

• ground- based platforms
• airborne platforms
• spaceborne platforms

Question 25

he fact that the processes of dust emis- sion and transport over Iraq are similar to those observed in

Answer 25

North Africa gives us confidence that the simulation of these processes by the meso-NH should be accurate even though we only have a lim- ited dataset to compare it to.

Question 26

In Iraq, emissions can occur over a variety of surfaces and may be highly variable depending on

Answer 26

the type of synoptic situation

Question 27

deserts occupy approximately …………. of the country as well as ……………..

Answer 27

170,000 km2 and cover the western and southern part

the Jazeera area

Question 28

These large deserts contribute to the overall dust load over the country, even though

Answer 28

noted that the Total Ozone Mapping Spectrometer (TOMS) sensor does not show any substantial dust activity in these desert regions.

Question 29

According to Prospero et al. (2002), the most intense dust activity occurs

Answer 29

south of 32N, 200 km southeast of Baghdad

Question 30

According to Prospero et al. (2002), the most intense dust activity occurs south of 32N, 200 km southeast of Baghdad. They have shown that dust activity in ……………. is present

Answer 30

the Tigris-Euphrates basin

• all year round
• maximum in July
• reduced by september-november

Question 31

he most intense dust activity occurs south of 32N, 200 km southeast of Baghdad. They have shown that dust activity in the Tigris-Euphrates basin is present all year round, reaches a maximum in July, and is much reduced by September–November. These sources are set in a

Answer 31

vast alluvial plain located in the Mesopotamian Plan that extends southward from 100 km north of Baghdad to the Persian Gulf.

Question 32

These sources are set in a vast alluvial plain located in the Mesopotamian Plan that extends southward from 100 km north of Baghdad to the Persian Gulf (Fig. 1d). The higher aerosol burdens during ……………….. may be interpreted as …………

Answer 32

summer

result of the combined effect of the seasonal drying of the numer- ous lakes and marshes and the strong northwesterly Shamal winds favoring dust erosion from the alluvial deposits in this region.

Question 33

These sources are set in a vast alluvial plain located in the Mesopotamian Plan that extends southward from 100 km north of Baghdad to the Persian Gulf (Fig. 1d). The higher aerosol burdens during summer may be interpreted as a result of the combined effect of the seasonal drying of the numer- ous lakes and marshes and the strong northwesterly Shamal winds favoring dust erosion from the alluvial deposits in this region. These deposits cover approximately

Answer 33

130,000 km²

Question 34

The seasonality of near surface winds over Iraq can be seen in fig 2 which shows

Answer 34

monthly 10-m winds from European Centre for Medium-range Weather Forecasts (ECMWF) ERA-Interim reanalysis (Dee et al., 2011) averaged for the period 2003–2012. In late spring and summer

Question 35

strong surface winds are seen to blow

Answer 35

across Syria, Iraq and over the Persian Gulf in connec- tion with wind surges from the Mediterranean

Question 36

strong surface winds are seen to blow across Syria, Iraq and over the Persian Gulf in connec- tion with wind surges from the Mediterranean. Summer Shamal winds are quite frequent and are clearly

Answer 36

discernible in monthly surface wind charts, particularly in June, July and August

Question 37

The orography of the region appears to play a major role: for instance,

Answer 37

the gap between the northern part of the elevated terrain to the west of the Arabic Peninsula and the Taurus Mountains in Turkey acts as a constriction, thereby accelerating the flow from the Mediterranean

Question 38

The general …………… orientation of the Shamal flow results from ……………………

Answer 38

northwest southeast

• the presence of high mountains of Turkey and Iran acting as a barrier for the impinging Mediterranean flow
• as well as the upsloping terrain to the west and downsloping terrain to the south.

Question 39

In winter …………………… flow is seen over…………………….

Answer 39

a much weaker surface flow (on average)

Syria and Iraq

Question 40

In winter (Figs. 2a– c and 1l), a much weaker surface flow (on average) is seen over Syria and Iraq (due to

Answer 40

the relatively small number of days with strong Shamal winds) while the strongest winds are seen over the Persian Gulf.

Question 41

In autumn ………….. flow is seen over ……………………

Answer 41

a weak surface flow (on average) is also seen over Syria and Iraq.

Question 42

Fig. 3 shows the monthly MODIS-derived AOD over the region, averaged for the period 2003–2012. It clearly shows large of AODs (in excess of …………..) over ………………. druing ………….

Answer 42

0.7

Syria and Iraq

the spring and summer months

Question 43

while rather weak AOD values are observed in

Answer 43

the winter

Question 44

In May, June and July, the largest AOD values are confined to ……….

Answer 44

the eastern part of Iraq, i.e. between the Euphrates and the foothills of the Zagros Mountains

Question 45

are confined to the eastern part of Iraq, i.e. between the Euphrates and the foothills of the Zagros Mountains, as previously noted byRao et al. (2001b). Furthermore, the MODIS dust maximum coin- cides with that of dust storm reports from meteorological stations (Middleton, 1986a,b). Middleton (1986b) reported an

Answer 45

extremely high frequency of dust storms in this region

Question 46

are confined to the eastern part of Iraq, i.e. between the Euphrates and the foothills of the Zagros Mountains, as previously noted byRao et al. (2001b). Furthermore, the MODIS dust maximum coin- cides with that of dust storm reports from meteorological stations (Middleton, 1986a,b). Middleton (1986b) reported an extremely high frequency of dust storms in this region, 43 per year at

Answer 46

Abadan, making it one of the dustiest places in southwest Asia.

Question 47

The maxi- mum AODs from MODIS are observed in

Answer 47

June

Question 48

reported an extremely high frequency of dust storms in this region, 43 per year at Abadan, making it one of the dustiest places in southwest Asia. The maxi- mum AODs from MODIS are observed in June (Fig. 3f). We hypoth- esize that this is related to

Answer 48

the number of Shamal events occurring during a given month in the summer (winter Shamal events being far less numerous than summer Shamal events) as well as the pres- ence of a nocturnal LLJ over Iraq during the summer Shamal period.

Question 49

This is now investigated using the 6-year dataset from the syn- optic stations over Iraq. Fig. 4 shows the monthly distribution of the number of events for which ……………………………. Mosul, Balad, Tallil and Abadan, for the period 2005–2010, as a function of the time of day

Answer 49

• the wind direction was from the 270 - 360 degrees sector
• the wind speed larger than 6 m/s
• visibility below 3.5 km

Question 50

it can be seen that a significant number of events for high winds and low visibilities occur in

Answer 50

late spring and throughout the summer (May–September)

Question 51

The largest numbers of events happen in

Answer 51

June and July (100+ high wind speed events and 40+ low visibil- ity events, respectively).

Question 52

A secondary maximum for the number of events for both high wind speeds and low visibilities is the month of

Answer 52

March

Question 53

It is also worth noting that for all months, the number of low visibility and high wind speed events occur at least

Answer 53

one hour after sunrise and at least one hour before sunset

Question 54

It is also worth noting that for all months, the number of low visibility and high wind speed events occur at least one hour after sunrise and at least one hour before sunset (Fig. 4c), suggest- ing that these events are related to

Answer 54

the diurnal evolution of the turbulence in the planetary boundary layer (PBL).

Question 55

It is also worth noting that for all months, the number of low visibility and high wind speed events occur at least one hour after sunrise and at least one hour before sunset (Fig. 4c), suggest- ing that these events are related to the diurnal evolution of the turbulence in the planetary boundary layer (PBL). Similar distribu- tions of events were also obtained for

Answer 55

different thresholds on wind speed and surface horizontal visibility

Question 56

All SYNOP stations south of Mosul exhibit

Answer 56

the typical maximum number of high wind speed and low visibility events between sun- rise and sunset in the spring and summer

Question 57

All SYNOP stations south of Mosul exhibit the typical maximum number of high wind speed and low visibility events between sun- rise and sunset in the spring and summer indicating that

Answer 57

dust emissions over Iraq are related to surface wind speed maxima which occur in the hours after sunrise as the result of the downward transfer of momentum from the Shamal-related LLJ to the surface due to turbulent mixing after the onset of solar heating,

Question 58

All SYNOP stations south of Mosul exhibit the typical maximum number of high wind speed and low visibility events between sun- rise and sunset in the spring and summer indicating that dust emissions over Iraq are related to surface wind speed maxima which occur in the hours after sunrise as the result of the downward transfer of momentum from the Shamal-related LLJ to the surface due to turbulent mixing after the onset of solar heating, as in

Answer 58

Bodélé depression area (Chad)

Question 59

All SYNOP stations south of Mosul exhibit the typical maximum number of high wind speed and low visibility events between sun- rise and sunset in the spring and summer indicating that dust emissions over Iraq are related to surface wind speed maxima which occur in the hours after sunrise as the result of the downward transfer of momentum from the Shamal-related LLJ to the surface due to turbulent mixing after the onset of solar heating, as in Bodélé depression area (Chad)

For instance, distributions of events similar to the one observed in Tallil are obtained for

Answer 59

Balad (central Iraq,Fig. 4b) and Abadan (southern Iran, Fig. 4d).

Question 60

In Mosul, the number of high wind speed events is seen to

Answer 60

spread more or less evenly throughout the day for the period May–July (Fig. 4a), and to be maximum around 1000 UTC.

Question 61

In Mosul, ………………….. visibility events are observed (………) likely reflecting ……….

Answer 61

very few low

(5 events or less)

a lack of dust source

Question 62

Furthermore, observations in Northwest Africa have highlighted the fact that the LLJ related dust emissions generally occurred between

Answer 62

0900 and 1200 LT before the overpass time of MODIS on AQUA

meaning that most dust plumes associated with LLJ dynamics are detected by MODIS

Question 63

Over Iraq, the MODIS on AQUA overpass (1230 UTC) occurs

Answer 63

after or during the maximum of dust mobilization for Balad, Tallil and Abadan

Question 64

Therefore, the large monthly averaged AOD values observed in Fig. 3 around 1230 UTC over Iraq in

Answer 64

the spring and early summer are consistent with dust emissions related to the existence of a quasi-permanent Shamal-related LLJ (and the large near surface wind speeds associated with turbulent downward momentum transport).

Question 65

On the other hand, the lack of large monthly mean AODs during the rest of the year suggest

Answer 65

more sporadic high near surface wind episodes, consistent with the fron- tal nature of the winter Shamal (Abdi Vishkaee et al., 2012) and the fact that only few such events are observed per month during the winter.

Question 66

On the other hand, the lack of large monthly mean AODs during the rest of the year suggest more sporadic high near surface wind episodes, consistent with the fron- tal nature of the winter Shamal (Abdi Vishkaee et al., 2012) and the fact that only few such events are observed per month during the winter. These results are consistent with those found by Yu et al. (2016), whom investigated

Answer 66

the correlation between Shamal event frequency and dust activity on the climatology and interannual time scales and concluded that the summer dust activities in Iraq are often triggered by Shamal.

Question 67

In this study, we investigate the diurnal evolution of the summer Shamal wind (a

Answer 67

quasi-permanent low-level northwesterly wind feature)

Question 68

and its role in dust emission and transport over Iraq, and detail the processes at play on the basis of a numerical simu- lation for a given, representative case study (25 June–3 July 2010), using observations and a numerical simulation performed with

Answer 68

the mesoscale model meso-NH.

Question 69

Dust emissions are associated with the

Answer 69

downward transfer of momentum from the nocturnal Shamal- related LLJ to the surface due to turbulent mixing after solar heat- ing commences each day.

Question 70

The case study highlights that the dust load during summer Shamal events exhibits large diurnal variabil- ity, with a daily

Answer 70

minimum value of 1 Tg around 0600 UTC and a daily peak of 2.5 Tg or more around 1500 UTC

Question 71

Shamal events exhibits large diurnal variabil- ity, with a daily minimum value of 1 Tg around 0600 UTC and a daily peak of 2.5 Tg or more around 1500 UTC, and is driven by

Answer 71

the diurnal cycle of the near surface wind speed.

Question 72

The case study highlights that the dust load during summer Shamal events exhibits large diurnal variabil- ity, with a daily minimum value of 1 Tg around 0600 UTC and a daily peak of 2.5 Tg or more around 1500 UTC, and is driven by the diurnal cycle of the near surface wind speed. This finding is consistent with

Answer 72

those from Yu et al. (2016), which were based on ground observations from weather stations in the climatology per- spective.

Question 73

It is important to note that the dust load peak associated with the summer Shamal is on the same order as those

Answer 73

also derived from simulations downstream of the Bodélé depression (Chad), estimated to be on the order of 2.7 Tg

Question 74

Bodélé is known to be one of the most

Answer 74

prolific dust sources on Earth

Question 75

Furthermore, near surface dust concentrations associated with these dust loads in

Answer 75

southern Iraq (e.g. Tallil), western Iran (e.g. Aba- dan) and over Saudi Arabia are simulated to reach values in excess of 3000 ug m^-3 for periods of 4–6 days, and also simulated to never fall below 100 ug m^-3.

Question 76

The estimation of the dust load associated with the Shamal summer wind was computed from

Answer 76

three indepen- dent datasets, i.e. using MODIS and SEVIRI derived AODs and directly from the simulations.

Question 77

The estimation of the dust load associated with the Shamal summer wind was computed from three indepen- dent datasets, i.e. using MODIS and SEVIRI derived AODs and directly from the simulations. The three datasets gave

Answer 77

roughly the same estimate.

Question 78

In general, dust emission by Shamal winds over Iraq was well reproduced by

Answer 78

the model. However, a better repre- sentation in dust models of dust sources in Syria, Jordan and the Sinai Peninsula especially alluvial dust sources is suggested for future studies given the nature of the dust sources in this region.