**5.3 Dynamical characteristics**

*Habitats of the World - Biodiversity and Threats*

in MERRA are much less (~40 J kg<sup>−</sup><sup>1</sup>

CAPE during the spells, it is clear from the analysis that ERA data reproduce similar

Spatial variability of anomalous CAPE during wet and dry spells over SE peninsular India from the reanalysis products is shown in **Figure 12**. Note that, here, main focus is to find out the difference in dry (**Figure 12 (a)**-**(c)**) and wet (**Figure 12 (d)**-**(f)**) spells over SE peninsular India, and therefore, the analysis is restricted only to that region. It is clear from **Figure 12** that during wet spell, CAPE is larger in all the products [47]. These large CAPE values are not confined to single station but rather observed all over southeastern peninsular India. In contrast, negative CAPE values are seen during dry spell in all the reanalysis products. These −ve CAPE magnitudes, during dry spell, reconfirms that the thermal stability of the atmosphere during dry spell is significantly less for convection to trigger. Though there are similarities that exist among the reanalysis products, slight differences in magnitudes are noted especially during dry spell. For example, magnitudes of anomalous CAPE

) than ERA (~200 J kg<sup>−</sup><sup>1</sup>

are perhaps due to various convective parameterizations employed in the reanalysis

imperative to understand the observed differences in CAPE between spells. In order to answer this, several plausible mechanisms are examined to explain the observed

*Spatial distribution of anomalous CAPE in dry ((a)-(c)) dry and wet (d)-(f) spells, from three reanalysis* 

*products, over the southeast peninsular India (reproduced from the [48]).*

Further, it is also noted from the buoyancy profiles during the spells that majority of positive buoyancy profiles show two peaks during dry spell and single upper tropospheric peak in wet spells at most of the grid points over southeast peninsular India (see Table 5 in [48]). Overall, majority of the buoyancy profiles, i.e., ~64%, exhibit bimodal distribution in dry spell, while single-peak buoyancy profiles are more prominent in wet spell (~56%), indicating the difference in the vertical distribution of parcel thermal buoyancy is not confined to single station but is a characteristic feature over the entire SE India. The analysis showed that, in

products and also the vertical resolutions of the data products used.

this region, CAPE is higher in wet spell than in dry spell by ~1000 J kg<sup>−</sup><sup>1</sup>

). These differences

. Now it is

CAPE variation between spells as obtained by radiosonde measurements.

**116**

**Figure 12.**

In the previous sections characteristics of wet and dry spells are studied with respect to the thermodynamical point of view. The analysis reveals significant variability in surface moisture and temperature, vertical structure, and also CAPE between spells, which clearly indicates the thermal structure, available energy, and their forcing are different in spells over SE peninsular India. Therefore, one would expect differences in circulation features during wet and dry spells. Thus, in the present section differences in mean wind, vertical structure and diurnal variation with a special emphasis on monsoon quasi permanent systems (likes of LLJ and TEJ) over south eastern peninsular India are studied.

Majority of the data were obtained by collocated instruments available at Gadanki. Surface winds during the spells are measured from automatic weather station (AWS) along with Doppler sound detection and ranging (SODAR) wind components in the height region from 60 m to 1 km. Zonal and meridional winds above 1 km to upper troposphere (~18 km) are derived from low atmospheric wind profiler (LAWP) and Indian mesosphere-stratosphere and troposphere radar (IMSTR). Note that, although the instruments were not operated simultaneously as they were deployed in different years, it is believed that the mean winds represent the overall vertical structure and variability.

**Figure 13** shows mean vertical profiles of mean wind and deviation during dry and wet spells of the monsoon over Gadanki. Since measurements utilized to generate this vertical wind structure by IMSTR, LAWP, SODAR, and AWS were not simultaneous, composite vertical profiles were not constructed. Rather, **Figure 13** shows average wind variation between spells in different altitude ranges (surface, obtained from AWS; 60 m to 1 km, obtained from SODAR; 600 m to 4 km, obtained from LAWP; and 3.6 to 19 km, obtained from IMSTR) [52].

Mean surface winds from AWS measurements (**Figure 13c**) during wet spells are relatively weaker than in dry spell, but the differences in zonal and meridional winds between the spells are not significant. However, the wind direction remained southwesterly in both spells. SODAR winds in the height region of 60 m–1 km remain northwesterly to westerly but exhibit large vertical variation in magnitude, particularly the zonal component. Zonal wind component attains their peak strength in the height region 200–500 m during both the spells, and in particular the intensity of zonal winds is stronger during dry spells (~4 ms<sup>−</sup><sup>1</sup> ) than wet spell (<2 ms<sup>−</sup><sup>1</sup> ), and further, the maximum difference between the spells is found in the height region of nocturnal low-level jet (NLLJ). In contrast, meridional winds are weak in amplitude (~1 ms<sup>−</sup><sup>1</sup> ) during both the spells and do not show any significant differences between the spells. In the height regions from 600 m to 4 km, LAWP-derived winds continued to be westerly to northwesterly in both spells. The presence of LLJ is clearly seen in the zonal wind component, and interestingly, the height of LLJ peak varies during both spells (e.g., at 2.25 and 1.35 km in dry and wet spells, respectively). In addition, magnitude of the LLJ is also different with enhanced LLJ in the dry spell (16.8 ms<sup>−</sup><sup>1</sup> ) than in wet spell (9.8 ms<sup>−</sup><sup>1</sup> ). Interestingly, the difference in zonal wind between the spells is more pronounced above 1.5 km.

#### **Figure 13.**

*Vertical profiles of (left column) zonal and (right column) meridional winds for wet and dry spells obtained from different instruments ((a) MST radar (1995–2013), (b) LAWP (1999–2000 and 2010–2011), and (c) SODAR (2007–2009) and AWS (2006–2013)). The average wind shown at 0 km (or surface) in Figure 13c is obtained from AWS. Vertical profiles shown in Figure 13a–c are daily averages. The standard deviation is represented with error bars. Years in the brackets indicate data averaging periods (source from [52]).*

In contrary, the magnitude of meridional winds is relatively small and does not show significant variation between spells. IMSTR winds reveal that the vertical structure of wind in the height region of 3.6–19 km is different in both spells. There is a significant difference in vertical structure of winds from IMSTR, in the height region from 3.6 to 19 km, in both wet and dry spells (**Figure 13a**). These differences are pronounced in the lower and middle troposphere (below 8 km). The zonal wind profiles show typical summer monsoon circulation with low-level westerlies and strong upper tropospheric easterlies. Wind reversal height (i.e., from westerly to easterly), however, is different during both monsoon spells. The depth of westerlies is relatively shallow (deep) during the wet (dry) spell with zonal wind reversal occurring below 6 (8) km and then turns to easterly. On the other hand, the TEJ strength is found to be nearly the same in both spells with an average value of ~30 ms<sup>−</sup><sup>1</sup> . The height of the TEJ maximum is also found to be nearly the same during both spells (~16 km).

This section discusses the differences in the spatial variability of the jet streams between the spells. Composites of LLJ and TEJ for wet and dry spells and the wind anomaly (mean wind for dry spell-mean wind for wet spell) are estimated. Note that the main idea is to study the spatial variability of LLJ and TEJ when the monsoon convection is weak or active over southeast India. It allows us to examine the spatial extent of observed wind differences at Gadanki.

**Figure 14** exhibits the spatial variation of mean zonal wind pattern for dry (**Figure 14a**) and wet (**Figure 14b**) spells and their difference (**Figure 14c**) on

**119**

**Figure 14.**

mass during the wet spell.

*Wet and Dry Spells over Southeast Peninsular India DOI: http://dx.doi.org/10.5772/intechopen.81836*

850 hPa level. Spatial distribution of the standard deviation of means for dry and wet spells is shown in **Figure 14d** and **e**, respectively. One commonality is the presence of LLJ in both the spells albeit with different magnitude and spatial distribution. During the dry spell (**Figure 14a**), the core of the LLJ splits over the Arabian Sea with one branch (say first branch) passing over the southern peninsular India centered around 16°N and the other toward southeast and veers cyclonically (second branch) before merging with the first branch in the Bay of Bengal (near the coast of Malay peninsula). On the other hand, only one branch (second branch) is present during the wet spell (**Figure 14b**). This splitting of LLJ in the Arabian Sea can be attributed to barotropic instability [49]. In this study, the splitting of LLJ is clearly evident during the dry spell (analogous to all-India active spell) [50, 51]. The presence of southward branch of LLJ during the break spell as reported by [48] is also seen here. In fact, this second branch is present in both spells with similar magnitude, as seen by the small wind anomaly present in that region (**Figure 14c**). **Figure 14c** clearly shows that large differences exist between the spells in LLJ magnitude and its spatial variation. A band of large positive wind anomaly passes over the Arabian Sea, Peninsular

*Mean zonal wind on 850 hPa level from MERRA data for (a) dry and (b) wet spells, during 1995–2013, showing the spatial variation of LLJ. The black dashed line in Figure 4a and b represents 10 ms<sup>−</sup><sup>1</sup>*

*the difference in LLJ between spells (dry-wet). The dot denotes the location of Gadanki. (d and e) the spatial distribution of standard deviation of mean values for dry and wet spells, respectively (source from [52]).*

India, Bay of Bengal, and Malaysia with a maximum (~6 ms<sup>−</sup><sup>1</sup>

Peninsular region. This large wind anomaly is significant and is occurring mainly due to the absence of first branch of LLJ during the wet spell. A negative anomaly in zonal wind is also observed in two regions, just south of the equator and near foot hills of the Himalayas. In general, the low-level westerly winds turn cyclonically in the North Bay of Bengal and become easterlies. These easterlies are clearly seen during the dry spell (or all-India active spell) (**Figure 14a**). As the monsoon trough moves northward to foot hills of the Himalayas during wet spell (or all-India break spell), the magnitude of easterlies became very weak (**Figure 14b**). In fact, the easterlies are completely absent over the Indian land-

Spatial variation of mean zonal wind and standard deviation during wet and dry spells along with zonal wind difference between the spells at 100 hPa level is described in **Figure 15**. The easterly winds are strong in both spells and seen

) over the Southern

 *contour. (c)* 

#### **Figure 14.**

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In contrary, the magnitude of meridional winds is relatively small and does not show significant variation between spells. IMSTR winds reveal that the vertical structure of wind in the height region of 3.6–19 km is different in both spells. There is a significant difference in vertical structure of winds from IMSTR, in the height region from 3.6 to 19 km, in both wet and dry spells (**Figure 13a**). These differences are pronounced in the lower and middle troposphere (below 8 km). The zonal wind profiles show typical summer monsoon circulation with low-level westerlies and strong upper tropospheric easterlies. Wind reversal height (i.e., from westerly to easterly), however, is different during both monsoon spells. The depth of westerlies is relatively shallow (deep) during the wet (dry) spell with zonal wind reversal occurring below 6 (8) km and then turns to easterly. On the other hand, the TEJ strength is found to be nearly the same in both spells with an average value

*error bars. Years in the brackets indicate data averaging periods (source from [52]).*

*Vertical profiles of (left column) zonal and (right column) meridional winds for wet and dry spells obtained from different instruments ((a) MST radar (1995–2013), (b) LAWP (1999–2000 and 2010–2011), and (c) SODAR (2007–2009) and AWS (2006–2013)). The average wind shown at 0 km (or surface) in Figure 13c is obtained from AWS. Vertical profiles shown in Figure 13a–c are daily averages. The standard deviation is represented with* 

. The height of the TEJ maximum is also found to be nearly the same

This section discusses the differences in the spatial variability of the jet streams between the spells. Composites of LLJ and TEJ for wet and dry spells and the wind anomaly (mean wind for dry spell-mean wind for wet spell) are estimated. Note that the main idea is to study the spatial variability of LLJ and TEJ when the monsoon convection is weak or active over southeast India. It allows us to examine the

**Figure 14** exhibits the spatial variation of mean zonal wind pattern for dry (**Figure 14a**) and wet (**Figure 14b**) spells and their difference (**Figure 14c**) on

**118**

of ~30 ms<sup>−</sup><sup>1</sup>

**Figure 13.**

during both spells (~16 km).

spatial extent of observed wind differences at Gadanki.

*Mean zonal wind on 850 hPa level from MERRA data for (a) dry and (b) wet spells, during 1995–2013, showing the spatial variation of LLJ. The black dashed line in Figure 4a and b represents 10 ms<sup>−</sup><sup>1</sup> contour. (c) the difference in LLJ between spells (dry-wet). The dot denotes the location of Gadanki. (d and e) the spatial distribution of standard deviation of mean values for dry and wet spells, respectively (source from [52]).*

850 hPa level. Spatial distribution of the standard deviation of means for dry and wet spells is shown in **Figure 14d** and **e**, respectively. One commonality is the presence of LLJ in both the spells albeit with different magnitude and spatial distribution. During the dry spell (**Figure 14a**), the core of the LLJ splits over the Arabian Sea with one branch (say first branch) passing over the southern peninsular India centered around 16°N and the other toward southeast and veers cyclonically (second branch) before merging with the first branch in the Bay of Bengal (near the coast of Malay peninsula). On the other hand, only one branch (second branch) is present during the wet spell (**Figure 14b**). This splitting of LLJ in the Arabian Sea can be attributed to barotropic instability [49]. In this study, the splitting of LLJ is clearly evident during the dry spell (analogous to all-India active spell) [50, 51]. The presence of southward branch of LLJ during the break spell as reported by [48] is also seen here. In fact, this second branch is present in both spells with similar magnitude, as seen by the small wind anomaly present in that region (**Figure 14c**). **Figure 14c** clearly shows that large differences exist between the spells in LLJ magnitude and its spatial variation. A band of large positive wind anomaly passes over the Arabian Sea, Peninsular India, Bay of Bengal, and Malaysia with a maximum (~6 ms<sup>−</sup><sup>1</sup> ) over the Southern Peninsular region. This large wind anomaly is significant and is occurring mainly due to the absence of first branch of LLJ during the wet spell. A negative anomaly in zonal wind is also observed in two regions, just south of the equator and near foot hills of the Himalayas. In general, the low-level westerly winds turn cyclonically in the North Bay of Bengal and become easterlies. These easterlies are clearly seen during the dry spell (or all-India active spell) (**Figure 14a**). As the monsoon trough moves northward to foot hills of the Himalayas during wet spell (or all-India break spell), the magnitude of easterlies became very weak (**Figure 14b**). In fact, the easterlies are completely absent over the Indian landmass during the wet spell.

Spatial variation of mean zonal wind and standard deviation during wet and dry spells along with zonal wind difference between the spells at 100 hPa level is described in **Figure 15**. The easterly winds are strong in both spells and seen

#### **Figure 15.**

*Same as Figure 14 but for zonal winds at 100 hPa level, showing the TEJ variation. The black thin and thick solid lines in Figure 15a and b represent 24 and 28 ms<sup>−</sup><sup>1</sup> contours, respectively (source from [52]).*

prominently between 10°N and 20°N with winds as large as 30 ms<sup>−</sup><sup>1</sup> corroborating the radar observations made at Gadanki (**Figure 13a**). However, longitudinal extent of TEJ during dry spell is found to be more than in wet spell. It can be evidenced by 28 ms<sup>−</sup><sup>1</sup> (thick black solid line) and 26 ms<sup>−</sup><sup>1</sup> contour (thin black solid line) of TEJ. For instance, the 26 ms<sup>−</sup><sup>1</sup> contour is seen between the longitudes 40°E and 100°E during the dry spell, while it is only confined between 45 E and 95°E during the wet spell. Earlier, [49] observed a significant ISV in TEJ axis on 200 hPa level. They observed the axis of the TEJ along 15°N during the break spell, while a southward shift in the TEJ axis is observed during the active spell at 70°E. Such a north–south shift in TEJ axis is not observed in either of the spells here. The axis is found to be aligned along ~15°N latitude during both the spells.

#### **6. Summary, conclusion, and discussion**

Synthesis of spatial and vertical structures and regional characteristics of wet and dry spells over southeast peninsular India is presented in this chapter. In spite of its importance, not many reports exist on rainfall and its variation on different temporal scales over this region during southwest monsoon, partly because the rainfall in this region is relatively less, and it forms only a minor part of all-India rainfall (see **Figure 3a**). With the goal in mind, an attempt has been made to understand differences in thermal and dynamical characteristics and energetics of the atmosphere between wet and dry spells of the Indian summer monsoon over the southeast India. To better understand the aforementioned processes, data collected with a suite of unique instruments at NARL, model reanalysis data sets, and satellite rainfall products are effectively utilized.

It is observed that the difference in the thermal structure between wet and dry spells is significant only in the lower troposphere (<2–3 km). The distributions and mean CAPE values, which are measures of thermal instability, for wet and dry spells, are found to be different. Analysis indicates that mean CAPE in wet spell is found to be higher than that of in dry spell by ~1000 J kg<sup>−</sup><sup>1</sup> . The vertical extent of positive buoyancy profiles is deep during wet spells, while most of the buoyancy profiles during dry spells are limited in vertical extent. Further, the negative buoyancy areas are seen

**121**

**Acronyms**

**Acknowledgements**

*Wet and Dry Spells over Southeast Peninsular India DOI: http://dx.doi.org/10.5772/intechopen.81836*

shearing apart the weakly buoyant updraft.

in most of the profiles during dry spell, and they are mostly centered on two height regions, ~700 and ~500 hPa. They, probably, are due to the strong inversions and stable layers present at those altitudes. The convection growth is limited in dry spells due to the presence of strong stable layers, weak CAPE, and a relatively dry environment. Reanalysis data products indicate CAPE is higher in wet spell than in dry spell over the entire southeast peninsular India. Majority of buoyancy profiles show only one peak during wet spell, while bimodal vertical distribution is seen predominantly in dry spell. From this analysis it is found that the differences in CAPE and buoyancy vertical structure between wet and dry spells are not only confined to Gadanki but rather observed all over southeastern peninsular India, and they are characteristic features of wet and dry spells. Several possible mechanisms are invoked to explain observed CAPE differences between spells, i.e., rapid rebuild-up of the instability, moistening of the atmosphere due to the evaporation of surface moisture in wet spell, enhanced downdrafts engendered by evaporative cooling, and drop dragging in dry spell. The synthesis of all measurements and estimates indicate that the observed weak CAPE in dry spell may not be sufficient to overshoot the frequent stable layers occurring in this spell. Further, the strong (magnitude) and deep (in height) low-level wind shear observed in dry spell seems to be

Diurnal variation of winds from surface to the lower stratosphere is studied during different spells of the monsoon. It is observed that, over the study region, the surface and low-level mean winds are stronger during dry spells. The surface wind (both zonal and meridional) exhibits a clear diurnal cycle with strong (weak) wind during day (night) in both spells. Both the amplitude and time of wind maxima change with the altitude. For instance, the zonal wind maxima observed at noon near the surface is shifted to early morning in the height region of 400 m–1.5 km (1 km) and then systematically to evening (noon) in the height region of 3–6 km (1–2.5 km) in dry (wet) spell. The depth of westerlies is deeper in dry spell than in wet spell. Also, the zonal wind reversal height shows clear diurnal variation in wet spell, while it is nearly the same in dry spell. The amplitude of the diurnal cycle increases with altitude up to 2 km and then decreases. Largest amplitudes of the diurnal cycle (>8 m s<sup>−</sup><sup>1</sup>

found in the height region of 1–2 km. The splitting of LLJ into two branches over the Arabian Sea is quite pronounced in dry spell, with one branch passing over the peninsular India and the other branch veering cyclonically and joins the first branch in the Bay of Bengal. The strength and the axis of TEJ do not vary much between spells. These variations are compared and contrasted with earlier reports on jet streams. The diagnostics made with the in situ observations and reanalysis products and the key results obtained can be exploited for the modeling purpose for better

The author would like to thank the director of the National Atmospheric Research Laboratory, Gadanki, for providing necessary facilities to carry out the work. The author would also like to thank Dr. T. Narayana Rao, NARL, for provid-

ing critical comment and helpful discussion in shaping out this work.

prediction of subseasonal variability of rainfall regionally.

ITCZ intertropical convergence zone TCZ tropical convergence zone

) are

#### *Wet and Dry Spells over Southeast Peninsular India DOI: http://dx.doi.org/10.5772/intechopen.81836*

*Habitats of the World - Biodiversity and Threats*

prominently between 10°N and 20°N with winds as large as 30 ms<sup>−</sup><sup>1</sup>

(thick black solid line) and 26 ms<sup>−</sup><sup>1</sup>

found to be aligned along ~15°N latitude during both the spells.

**6. Summary, conclusion, and discussion**

rainfall products are effectively utilized.

to be higher than that of in dry spell by ~1000 J kg<sup>−</sup><sup>1</sup>

the radar observations made at Gadanki (**Figure 13a**). However, longitudinal extent of TEJ during dry spell is found to be more than in wet spell. It can be evidenced

*Same as Figure 14 but for zonal winds at 100 hPa level, showing the TEJ variation. The black thin and thick* 

Synthesis of spatial and vertical structures and regional characteristics of wet and dry spells over southeast peninsular India is presented in this chapter. In spite of its importance, not many reports exist on rainfall and its variation on different temporal scales over this region during southwest monsoon, partly because the rainfall in this region is relatively less, and it forms only a minor part of all-India rainfall (see **Figure 3a**). With the goal in mind, an attempt has been made to understand differences in thermal and dynamical characteristics and energetics of the atmosphere between wet and dry spells of the Indian summer monsoon over the southeast India. To better understand the aforementioned processes, data collected with a suite of unique instruments at NARL, model reanalysis data sets, and satellite

It is observed that the difference in the thermal structure between wet and dry spells is significant only in the lower troposphere (<2–3 km). The distributions and mean CAPE values, which are measures of thermal instability, for wet and dry spells, are found to be different. Analysis indicates that mean CAPE in wet spell is found

buoyancy profiles is deep during wet spells, while most of the buoyancy profiles during dry spells are limited in vertical extent. Further, the negative buoyancy areas are seen

100°E during the dry spell, while it is only confined between 45 E and 95°E during the wet spell. Earlier, [49] observed a significant ISV in TEJ axis on 200 hPa level. They observed the axis of the TEJ along 15°N during the break spell, while a southward shift in the TEJ axis is observed during the active spell at 70°E. Such a north–south shift in TEJ axis is not observed in either of the spells here. The axis is

corroborating

contour (thin black solid line) of

. The vertical extent of positive

contour is seen between the longitudes 40°E and

 *contours, respectively (source from [52]).*

**120**

by 28 ms<sup>−</sup><sup>1</sup>

**Figure 15.**

TEJ. For instance, the 26 ms<sup>−</sup><sup>1</sup>

*solid lines in Figure 15a and b represent 24 and 28 ms<sup>−</sup><sup>1</sup>*

in most of the profiles during dry spell, and they are mostly centered on two height regions, ~700 and ~500 hPa. They, probably, are due to the strong inversions and stable layers present at those altitudes. The convection growth is limited in dry spells due to the presence of strong stable layers, weak CAPE, and a relatively dry environment.

Reanalysis data products indicate CAPE is higher in wet spell than in dry spell over the entire southeast peninsular India. Majority of buoyancy profiles show only one peak during wet spell, while bimodal vertical distribution is seen predominantly in dry spell. From this analysis it is found that the differences in CAPE and buoyancy vertical structure between wet and dry spells are not only confined to Gadanki but rather observed all over southeastern peninsular India, and they are characteristic features of wet and dry spells. Several possible mechanisms are invoked to explain observed CAPE differences between spells, i.e., rapid rebuild-up of the instability, moistening of the atmosphere due to the evaporation of surface moisture in wet spell, enhanced downdrafts engendered by evaporative cooling, and drop dragging in dry spell. The synthesis of all measurements and estimates indicate that the observed weak CAPE in dry spell may not be sufficient to overshoot the frequent stable layers occurring in this spell. Further, the strong (magnitude) and deep (in height) low-level wind shear observed in dry spell seems to be shearing apart the weakly buoyant updraft.

Diurnal variation of winds from surface to the lower stratosphere is studied during different spells of the monsoon. It is observed that, over the study region, the surface and low-level mean winds are stronger during dry spells. The surface wind (both zonal and meridional) exhibits a clear diurnal cycle with strong (weak) wind during day (night) in both spells. Both the amplitude and time of wind maxima change with the altitude. For instance, the zonal wind maxima observed at noon near the surface is shifted to early morning in the height region of 400 m–1.5 km (1 km) and then systematically to evening (noon) in the height region of 3–6 km (1–2.5 km) in dry (wet) spell. The depth of westerlies is deeper in dry spell than in wet spell. Also, the zonal wind reversal height shows clear diurnal variation in wet spell, while it is nearly the same in dry spell. The amplitude of the diurnal cycle increases with altitude up to 2 km and then decreases. Largest amplitudes of the diurnal cycle (>8 m s<sup>−</sup><sup>1</sup> ) are found in the height region of 1–2 km. The splitting of LLJ into two branches over the Arabian Sea is quite pronounced in dry spell, with one branch passing over the peninsular India and the other branch veering cyclonically and joins the first branch in the Bay of Bengal. The strength and the axis of TEJ do not vary much between spells. These variations are compared and contrasted with earlier reports on jet streams.

The diagnostics made with the in situ observations and reanalysis products and the key results obtained can be exploited for the modeling purpose for better prediction of subseasonal variability of rainfall regionally.
