An Evaluation of the Impact of Pandemic Driven Lockdown on the Phytoplankton Biomass Over the North Indian Ocean Using Observations and Model

The unprecedented nationwide lockdown due to the ‘coronavirus disease 2019’ (COVID-19) affected humans and the environment in different ways. It provided an opportunity to examine the effect of reduced transportation and other anthropogenic activities on the environment. In the current study, the impact of lockdown on chlorophyll-a (Chl-a) concentration, an index of primary productivity, over the northern Indian Ocean (IO), is investigated using the observations and a physical-biogeochemical model. The statistics of model validation against observations shows a correlation coefficient of 0.85 (0.89), index of agreement as 0.90 (0.91). Root mean square error of 0.45°C (0.50°C) for sea surface temperature over the Bay of Bengal (BoB) (Arabian Sea, AS) is observed. The model results are analyzed to understand the upper-oceanic physical and biological processes during the lockdown. A comparison of the observed and model-simulated data during the lockdown period (March–June, 2020) and pre-pandemic period (March–June, 2019) shows significant differences in the physical (temperature and salinity) and biogeochemical (Chl-a concentration, nutrient concentration, and dissolved oxygen) parameters over the western AS, western BoB, and regions of Sri Lanka. During the pandemic, the reduced anthropogenic activities lead to a decrease in Chl-a concentration in the coastal regions of western AS and BoB. The enhanced aerosol/dust transport due to stronger westerly winds enhanced phytoplankton biomass in the western Arabian Sea (WAS) in May–June of the pandemic period.

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Long-Term Trends and Impact of SARS-CoV-2 COVID-19 Lockdown on the Primary Productivity of the North Indian Ocean

Frontiers in Marine Science ◽

10.3389/fmars.2021.669415 ◽

2021 ◽

Vol 8 ◽

Author(s):

N. Sunanda ◽

J. Kuttippurath ◽

R. Peter ◽

Kunal Chakraborty ◽

A. Chakraborty

Keyword(s):

Indian Ocean ◽

Interannual Variability ◽

Primary Productivity ◽

Virus Disease ◽

North Indian Ocean ◽

Chl A ◽

The North ◽

Biogeochemical Models ◽

The Impact

COrona VIrus Disease (COVID) 2019 pandemic forced most countries to go into complete lockdown and India went on complete lockdown from 24th March 2020 to 8th June 2020. To understand the possible implications of lockdown, we analyze the long-term distribution of Net Primary Productivity (NPP) in the North Indian Ocean (NIO) and the factors that influence NPP directly and indirectly, for the period 2003–2019 and 2020 separately. There exists a seasonal cycle in the relationship between Aerosol Optical Depth (AOD), Chlorophyll-a (Chl-a) and NPP in agreement with the seasonal transport of aerosols and dust into these oceanic regions. In Arabian Sea (AS), the highest Chl-a (0.58 mg/m3), NPP (696.57 mg/C/m2/day) and AOD (0.39) are observed in June, July, August, and September (JJAS). Similarly, maximum Chl-a (0.48 mg/m3) and NPP (486.39 mg/C/m2/day) are found in JJAS and AOD (0.27) in March, April, and May (MAM) in Bay of Bengal. The interannual variability of Chl-a and NPP with wind speed and Sea Surface Temperature (SST) is also examined, where the former has a positive and the latter has a negative feedback to NPP. The interannual variability of NPP reveals a decreasing trend in NPP, which is interlinked with the increasing trend in SST and AOD. The analysis of wind, SST, Chl-a, and AOD for the pre-lockdown, lockdown, and post lockdown periods of 2020 is employed to understand the impact of COVID-19 lockdown on NPP. The assessment shows the reduction in AOD, decreased wind speeds, increased SST and reduced NPP during the lockdown period as compared to the pre-lockdown, post-lockdown and climatology. This analysis is expected to help to understand the impact of aerosols on the ocean biogeochemistry, nutrient cycles in the ocean biogeochemical models, and to study the effects of climate change on ocean ecosystems.

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Effect of tropical cyclones on the Stratosphere-Troposphere Exchange observed using satellite observations over north Indian Ocean

10.5194/acp-2015-988 ◽

2016 ◽

Cited By ~ 3

Author(s):

M. Venkat Ratnam ◽

S. Ravindra Babu ◽

S. S. Das ◽

Ghouse Basha ◽

B. V. Krishnamurthy ◽

...

Keyword(s):

Water Vapor ◽

Indian Ocean ◽

Tropical Cyclones ◽

Lower Stratosphere ◽

North Indian Ocean ◽

Satellite Observations ◽

Upper Troposphere ◽

North West ◽

The North ◽

The Impact

Abstract. Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere-troposphere exchange (STE) process in the Upper Troposphere and Lower Stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the North Indian Ocean during 2007–2013 on the STE process is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) Radio Occultation (RO) measurements and ozone and water vapor concentrations in UTLS region are obtained from Aura-Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km from the centre of cyclone. In our earlier study we have observed decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K) and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within the 500 km from the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from cyclone centre whereas the enhancement in the water vapor in the lower stratosphere is more significant on south-east side extending from 500–1000 km away from the cyclone centre. We estimated the cross-tropopause mass flux for different intensities of cyclones and found that the mean flux from stratosphere to troposphere for cyclonic stroms is 0.05 ± 0.29 × 10−3 kg m−2 and for very severe cyclonic stroms it is 0.5 ± 1.07 × 10−3 kg m−2. More downward flux is noticed in the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget and consequentially the STE in the UTLS region.

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Anthropogenic iron deposition alters the ecosystem and carbon balance of the Indian Ocean over a centennial timescale

10.5194/egusphere-egu2020-21916 ◽

2020 ◽

Author(s):

Anh Pham ◽

Takamitsu Ito

Keyword(s):

Indian Ocean ◽

Arabian Sea ◽

Ocean Basin ◽

Ecosystem Dynamics ◽

Carbon Uptake ◽

The South ◽

Nutrient Deposition ◽

The North ◽

The Indian Ocean ◽

The Impact

<p>Phytoplankton growth in the Indian Ocean is generally limited by macronutrients (nitrogen: N and phosphorus: P) in the north and by micronutrient (iron: Fe) in the south. Increasing anthropogenic atmospheric deposition of N and dissolved Fe (dFe) into the ocean can thus lead to significant responses from marine ecosystems in this ocean basin. Previous modeling studies investigated the impacts of anthropogenic nutrient deposition on the ocean, but their results are uncertain due to incomplete representations of Fe cycling. We use a state-of-the-art ocean ecosystem and Fe cycling model to evaluate the transient responses of ocean productivity and carbon uptake in the Indian Ocean, focusing on the centennial time scale. The model incorporates all major external sources and represents a complicated internal cycling process of Fe, thus showing significant improvements in reproducing observations. Sensitivity simulations show that after a century of anthropogenic deposition, increased dFe stimulates diatoms productivity in the southern Indian Ocean poleward of 50&#8304;S and the southeastern tropics. Diatoms production weakens in the south of the Arabian Sea due to the P limitation, and diatoms are outcompeted there by coccolithophores and picoplankton, which have a lower P demand. These changes in diatoms and coccolithophores productions alter the balance between the organic and carbonate pumps in the Indian Ocean, increasing the carbon uptake in the south of 50&#8304;S and the southeastern tropics while decreasing it in the Arabian Sea. Our results reveal the important role of ecosystem dynamics in controlling the sensitivity of carbon fluxes in the Indian Ocean under the impact of anthropogenic nutrient deposition over a centennial timescale.</p>

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MEASURING POLICY BENEFITS OF THE CYCLONE SHELTER PROGRAM IN THE NORTH INDIAN OCEAN: PROTECTION FROM INTENSE WINDS OR HIGH STORM SURGES?

Climate Change Economics ◽

10.1142/s2010007817500117 ◽

2017 ◽

Vol 08 (04) ◽

pp. 1750011 ◽

Cited By ~ 18

Author(s):

S. NIGGOL SEO

Keyword(s):

Indian Ocean ◽

Low Income ◽

Arabian Sea ◽

Negative Binomial ◽

Storm Surges ◽

North Indian Ocean ◽

High Population Density ◽

Cyclone Intensity ◽

The North ◽

Cyclone Shelter

This paper provides a quantitative estimate of the policy benefit of the cyclone shelter program (CSP) implemented in Bangladesh. The present author examines all cyclones that were generated in the North Indian Ocean, both the Bay of Bengal and the Arabian Sea, from 1990 to 2015. A negative binomial (NB) model of cyclone fatalities against cyclone intensity finds that the CSP does little in protecting people’s lives against the high storm intensity. In contrast, a two-stage NB model of cyclone fatalities against the level of surges reveals that the CSP is vastly effective against storm surges. The number of fatalities is, on average, 75% smaller in the areas where the shelter program has been implemented against the areas without the program in response to the same level of storm surges. A set of Probit adoption models of adaptation options in response to cyclone surges and intensity reveals that the CSP has been directed to a low-income area with high population density, which is in contrast to the other strategies which have been increasingly adopted with higher income, e.g., cyclone trajectory projection technologies.

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Role of Rossby Waves in the Remote Effects of the North Indian Ocean Tropical Disturbances

Monthly Weather Review ◽

10.1175/mwr-d-12-00027.1 ◽

2012 ◽

Vol 140 (11) ◽

pp. 3620-3633 ◽

Cited By ~ 1

Author(s):

J. V. Ratnam ◽

S. K. Behera ◽

Y. Masumoto ◽

T. Yamagata

Keyword(s):

Saudi Arabia ◽

Indian Ocean ◽

Bay Of Bengal ◽

Arabian Sea ◽

Rossby Waves ◽

Temporal Distribution ◽

North Indian Ocean ◽

Positive Temperature ◽

The North ◽

Wide Range

Abstract Remote effects due to the tropical disturbances in the north Indian Ocean are investigated by analyzing long-lasting (≥5 days) tropical disturbances, which reached at least the strength of tropical storms. The present analysis is carried out for both the pre- and postmonsoon periods. The spatial and temporal distribution of the outgoing longwave radiation (OLR) during the premonsoon disturbances over the Bay of Bengal reveals several interesting features. Temporal distribution of the OLR anomalies shows that the intraseasonal oscillations play an important role in the formation of those disturbances. The spatial distribution of the OLR anomalies shows a dipole with negative OLR anomalies over the bay and positive OLR anomalies over the Indonesian region. The atmospheric response to the negative OLR anomalies results in positive temperature anomalies over northwest India, Pakistan, Afghanistan, Iran, and Saudi Arabia, remote from the disturbance; and the response to the positive anomalies causes slight increase in the sea surface temperature of the Arabian Sea. Negative OLR anomalies are also seen over western Japan due to the Rossby waves generated by the heating over the Bay of Bengal besides the enhancement of the so-called “Pacific–Japan” teleconnection pattern. However, the analysis shows that the postmonsoon disturbances over the Bay of Bengal and the disturbances formed over the Arabian Sea in both pre- and postmonsoon seasons do not develop remote teleconnections associated with the above type of Rossby wave mechanism. These results are significant for the short- to medium-range weather forecast over a wide range covering Japan, Pakistan, Afghanistan, Iran, and Saudi Arabia.

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Variability in dynamic and thermodynamic parameters in cyclogenesis over north Indian ocean

MAUSAM ◽

10.54302/mausam.v60i1.1015 ◽

2021 ◽

Vol 60 (1) ◽

pp. 61-72

Author(s):

A. MUTHUCHAMI

Keyword(s):

Indian Ocean ◽

Thermodynamic Parameters ◽

Bay Of Bengal ◽

Arabian Sea ◽

Threshold Level ◽

Reanalysis Data ◽

North Indian Ocean ◽

The North ◽

Static Instability ◽

The Difference

The two basins Arabian sea (ARS) and Bay of Bengal (BOB) of the North Indian Ocean (NIO) are having different dynamic and thermodynamic character and therefore ARS has subdued cyclone activity than BOB. In order to examine the difference between these basins in respect of various meteorological parameters, using NCEP/NCAR reanalysis data for the period 1971-2005 during the months of September to December the distribution of the dynamic and thermodynamic parameters are discussed. It is seen that sea surface temperature (SST) is not responsible for subdued activity over ARS as the SST over ARS and BOB is mostly above minimum threshold level. In respect of wind shear, during October in ARS north of 10° N is favourable for storm formation unlike September where the whole of Arabian sea except the region north of 20° N is inert to cyclone formation. The humidity factor is more pronounced in ARS for prohibiting storm formation than shear factor. In all the months static instability at 90° E is least and so the atmosphere is neutral throughout the period and consequence of it any small trigger in the lower level will induce the system to grow further. The BOB is more barotropic than ARS. There is a considerable difference exists in precipitation rate as a consequence of more stable atmosphere over Arabian sea than in Bay of Bengal even at the lower level.

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Tropospheric warming over the North Indian Ocean caused by the South Asian anthropogenic aerosols: possible implications

10.5194/acp-2021-969 ◽

2021 ◽

Author(s):

Suvarna Fadnavis ◽

Prashant Chavan ◽

Akash Joshi ◽

Sunil Sonbawne ◽

Asutosh Acharya ◽

...

Keyword(s):

Water Vapor ◽

Indian Ocean ◽

South Asia ◽

South Asian ◽

Bay Of Bengal ◽

Arabian Sea ◽

North Indian Ocean ◽

Carbonaceous Aerosols ◽

Anthropogenic Aerosols ◽

The North

Abstract. Atmospheric concentrations of South Asian anthropogenic aerosols and their transport play a key role in the regional hydrological cycle. Here, we use the ECHAM6-HAMMOZ chemistry-climate model to show the structure and implications of the transport pathways of these aerosols during spring. Our simulations indicate that large amounts of anthropogenic aerosols are transported from South Asia to the North Indian Ocean (the Arabian Sea and North Bay of Bengal). These aerosols are then lifted into the upper troposphere and lower stratosphere (UTLS) by the convection over the Arabian Sea and Bay of Bengal. In the UTLS, they are further transported to the southern hemisphere (30–40° S) and downward into the troposphere by the secondary circulation induced by the aerosol changes. The carbonaceous aerosols are also transported to the Arctic and Antarctic producing local heating (0.002–0.05 K d−1). The presence of anthropogenic aerosols causes negative radiative forcing (RF) at the TOA (0.90 ± 0.089 W m−2) and surface (−5.87 ± 0.31 W m−2) and atmospheric warming (+4.96 ± 0.24 W m−2) over South Asia (60° E–90° E, 8° N–23° N), except over the Indo-Gangetic plain (75° E–83° E, 23° N–30° N) where RF at the TOA is positive (+1.27 ± 0.16 W m−2) due to large concentrations of absorbing aerosols. The carbonaceous aerosols produced in-atmospheric heating along the aerosol column extending from the boundary layer to the UTLS (0.01 to 0.3 K d−1) and in the stratosphere globally (0.002 to 0.012 K d−1). The heating of the troposphere increases water vapor concentrations, which are then transported from the highly convective region (i.e. the Arabian Sea) to the UTLS (increasing water vapor by 0.02–0.06 ppmv).

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Principal component analysis of monthly mean Area surface temperature over the Arabian Sea, Bay of Bengal and north Indian Ocean for two Contrasting sets of monsoon years

MAUSAM ◽

10.54302/mausam.v44i1.3778 ◽

2021 ◽

Vol 44 (1) ◽

pp. 69-76

Author(s):

T. K. BALAKRISHNAN ◽

A. K. JASWAL ◽

S.S.. SINGH ◽

H. N. SRIVASTAVA

Keyword(s):

Indian Ocean ◽

Bay Of Bengal ◽

Arabian Sea ◽

Monsoon Rainfall ◽

Equatorial Indian Ocean ◽

Principal Component ◽

North Indian Ocean ◽

Orthogonal Function ◽

The North ◽

Extreme North

The spatial distribution and temporal variation of the monthly mean SSTA over the Arabian Sea, Bay of Bengal and the north Indian Ocean were investigated for a set of contrasting years of monsoon over the period 1961-80 for months April through July using Empirical Orthogonal Function (EOF) technique with a view to identify regions that are significantly related to the monsoon rainfall. Over 75% of the total variance is, explained by the first mode EOF. SSTA over the north and northeast Arabian Sea during pre-monsoon months were found to be possible indicators of the ensuing monsoon activity. The higher eigen vectors in May over northeast Arabian Sea may signal good monsoon and vice versa. In June there is a marked contrast in the distribution of SST over the Arabian Sea between the two sets of the years the eastern Arabian Sea IS warmer for the deficient monsoon years while the entire Arabian Sea except over the extreme north Arabian Sea is cool during good monsoon years. There is formation of SSTA over the equatorial Indian Ocean area close to Indonesian island commencing from May which is more marked in June and is positively correlated with seasonal rainfall activity over India.

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Sensitivity of Microphysical Schemes on the Simulation of Post-Monsoon Tropical Cyclones over the North Indian Ocean

Atmosphere ◽

10.3390/atmos11121297 ◽

2020 ◽

Vol 11 (12) ◽

pp. 1297

Author(s):

Gundapuneni Venkata Rao ◽

Keesara Venkata Reddy ◽

Venkataramana Sridhar

Keyword(s):

Indian Ocean ◽

Tropical Cyclones ◽

Socioeconomic Development ◽

Weather Prediction ◽

North Indian Ocean ◽

Sensitivity Experiments ◽

Post Monsoon ◽

The North ◽

Arw Model ◽

The Impact

Tropical Cyclones (TCs) are the most disastrous natural weather phenomenon, that have a significant impact on the socioeconomic development of the country. In the past two decades, Numerical Weather Prediction (NWP) models (e.g., Advanced Research WRF (ARW)) have been used for the prediction of TCs. Extensive studies were carried out on the prediction of TCs using the ARW model. However, these studies are limited to a single cyclone with varying physics schemes, or single physics schemes to more than one cyclone. Hence, there is a need to compare different physics schemes on multiple TCs to understand their effectiveness. In the present study, a total of 56 sensitivity experiments are conducted to investigate the impact of seven microphysical parameterization schemes on eight post-monsoon TCs formed over the North Indian Ocean (NIO) using the ARW model. The performance of the Ferrier, Lin, Morrison, Thompson, WSM3, WSM5, and WSM6 are evaluated using error metrics, namely Mean Absolute Error (MAE), Mean Square Error (MSE), Skill Score (SS), and average track error. The results are compared with Indian Meteorological Department (IMD) observations. From the sensitivity experiments, it is observed that the WSM3 scheme simulated the cyclones Nilofar, Kyant, Daye, and Phethai well, whereas the cyclones Hudhud, Titli, and Ockhi are best simulated by WSM6. The present study suggests that the WSM3 scheme can be used as the first best scheme for the prediction of post-monsoon tropical cyclones over the NIO.

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