scholarly journals Indian ocean marine biogeochemical variability and its feedback on simulated South Asia climate

2021 ◽  
Author(s):  
Dmitry V. Sein ◽  
Anton Y. Dvornikov ◽  
Stanislav D. Martyanov ◽  
William Cabos ◽  
Vladimir A. Ryabchenko ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Primary Production ◽  
Light Absorption ◽  
Large Scale ◽  
Monsoon Season ◽  
Light Attenuation ◽  
Convective Precipitation ◽  
Phytoplankton Primary Production ◽  
Cascading Effects ◽  
Subsurface Layers

Abstract. We investigate the effect of variable marine biogeochemical light absorption on Indian Ocean sea surface temperature (SST) and how this affects the South Asian climate. In twin experiments with a regional Earth System Model, we found that the average SST is lower over most of the domain when variable marine biogeochemical light absorption is taken into account, compared to the reference experiment with a constant light attenuation coefficient equal to 0.06 m-1. The most significant deviations (more than 1 °C) in SST are observed in the summer period. A considerable cooling of subsurface layers occurs, and the thermocline shifts upward in the experiment with the activated biogeochemical impact. Also, the phytoplankton primary production becomes higher, especially during periods of winter and summer phytoplankton blooms. The effect of altered SST variability on climate was investigated by coupling the ocean models to a regional atmosphere model. We find the largest effects on the amount of precipitation, particularly during the monsoon season. In the Arabian Sea, the reduction of the transport of humidity across the equator leads to a reduction of the large-scale precipitation in the eastern part of the basin, reinforcing the reduction of the convective precipitation. In the Bay of Bengal, it increases the large-scale precipitation, countering convective precipitation decline. Thus, the key impacts of including the full biogeochemical coupling with corresponding light attenuation, which in turn depends on variable chlorophyll-a concentration, include the enhanced phytoplankton primary production, a shallower thermocline, decreased SST and water temperature in subsurface layers, with cascading effects upon the model ocean physics which further translates into altered atmosphere dynamics.

scholarly journals Light absorption by marine cyanobacteria affects tropical climate mean state and variability

2018 ◽  
Vol 9 (4) ◽  
pp. 1283-1300 ◽  
Author(s):  
Hanna Paulsen ◽  
Tatiana Ilyina ◽  
Johann H. Jungclaus ◽  
Katharina D. Six ◽  
Irene Stemmler
Keyword(s):  
Light Absorption ◽  
Large Scale ◽  
Local Heating ◽  
Light Attenuation ◽  
Tropical Climate ◽  
Climate System ◽  
Radiative Heating ◽  
Subsurface Water ◽  
Marine Cyanobacteria ◽  
Tropical Ocean

Abstract. Observations indicate that positively buoyant marine cyanobacteria, which are abundant throughout the tropical and subtropical ocean, have a strong local heating effect due to light absorption at the ocean surface. How these local changes in radiative heating affect the climate system on the large scale is unclear. We use the Max Planck Institute Earth System Model (MPI-ESM), include light absorption by cyanobacteria, and find a considerable cooling effect on tropical sea surface temperature (SST) in the order of 0.5 K on a climatological timescale. This cooling is caused by local shading of subtropical subsurface water by cyanobacteria that is upwelled at the Equator and in eastern boundary upwelling systems. Implications for the climate system include a westward shift of the Walker circulation and a weakening of the Hadley circulation. The amplitude of the seasonal cycle of SST is increased in large parts of the tropical ocean by up to 25 %, and the tropical Pacific interannual variability is enhanced by approx. 20 %. This study emphasizes the sensitivity of the tropical climate system to light absorption by cyanobacteria due to its regulative effect on tropical SST. Generally, including phytoplankton-dependent light attenuation instead of a globally uniform attenuation depth improves some of the major model temperature biases, indicating the relevance of taking this biophysical feedback into account in climate models.

scholarly journals Seasonal prediction of cyclonic disturbances over the Bay of Bengal during summer monsoon season : Identification of potential predictors

MAUSAM ◽  
2021 ◽  
Vol 61 (4) ◽  
pp. 469-486
Author(s):  
M. MOHAPATRA ◽  
S. ADHIKARY
Keyword(s):  
Indian Ocean ◽  
Bay Of Bengal ◽  
Large Scale ◽  
Monsoon Season ◽  
Equatorial Indian Ocean ◽  
Seasonal Prediction ◽  
Reanalysis Data ◽  
Scale Field ◽  
Large Scale Field ◽  
Cyclonic Disturbances

The cyclonic disturbances (CD) over the Bay of Bengal during monsoon season have significant impact on rainfall over India. On many occasions, they cause flood leading to loss of lives and properties. Hence, any early information about the frequency of occurrence of such disturbances will help immensely the disaster managers and planners. However, the studies are limited on the seasonal prediction of CD over the Bay of Bengal unlike other Ocean basins of the world. Hence, a study has been undertaken to find out the potential predictors during the months of April and May for prediction of frequency of cyclonic disturbances over the Bay of Bengal during monsoon season (June – September). For this purpose, best track data of India Meteorological Department and large scale field parameters based on NCEP/NCAR reanalysis data have been analyzed for the period of 1948 – 2007.  The linear correlation analysis has been applied between frequency of CD and large scale field parameters based on NCEP/NCAR reanalysis data to find out the potential predictors.   The large scale field parameters over the equatorial Indian Ocean, especially over west equatorial Indian Ocean and adjoining Arabian Sea (up to 15° N) should be favourable in April and May with lower mean sea level pressure (MSLP), lower geopotential heights and stronger southerlies in lower and middle levels, along with stronger northerly components at upper level for higher frequency of CD during subsequent monsoon season. Consequently, there should be increase in relative humidity (RH) and precipitable water content and decrease in outgoing longwave radiation (OLR) and temperature at lower levels over this region during April and May for higher frequency of CD during subsequent monsoon  season. Comparing the area of significant correlation between frequency of CD and large scale field parameters and its stability from April to September, MSLP and geopotential heights are most influencing parameters followed by OLR, sea surface temperature, air temperature and RH at 850 hPa level.

scholarly journals Spatial Variation in Primary Production in the Eastern Indian Ocean

2021 ◽  
Vol 8 ◽  
Author(s):  
Haijiao Liu ◽  
Yuyao Song ◽  
Xiaodong Zhang ◽  
Guicheng Zhang ◽  
Chao Wu ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Primary Production ◽  
Carbon Fixation ◽  
Monsoon Season ◽  
Biological Data ◽  
Eastern Indian Ocean ◽  
Light Limitation ◽  
Photic Zone ◽  
Production Rates ◽  
Study Region

To examine the spatial pattern and controlling factors of the primary productivity (PP) of phytoplankton in the eastern Indian Ocean (EIO), deck-incubation carbon fixation (a 14C tracer technique) and the related hydrographic properties were measured at 15 locations during the pre-summer monsoon season (February–April 2017). There are knowledge gaps in the field observations of PP in the EIO. The estimated daily carbon production rates integrated over the photic zone ranged from 113 to 817 mgC m–2 d–1, with a mean of 522 mgC m–2 d–1. The mixed-layer integrated primary production (MLD-PP) ranged from 29.0 to 303.7 mgC m–2 d–1 (mean: 177.2 mgC m–2 d–1). The contribution of MLD-PP to the photic zone-integrated PP (PZI-PP) varied between 19 and 51% (mean: 36%). Strong spatial variability in the carbon fixation rates was found in the study region. Specifically, the surface primary production rates were relatively higher in the Bay of Bengal domain affected by riverine flux and lower in the equatorial domain owing to the presence of intermonsoonal Wyrtki jets, which were characterized by a depression of thermocline and nitracline. The PZI-PP exhibited a linear (positive) relationship with nutrient values, but with no significance, indicating a partial control of macronutrients and a light limitation of carbon fixation. As evident from the vertical profiles, the primary production process mainly occurred above the nitracline depth and at high photosynthetic efficiency. Phytoplankton (>5 μm), including dinoflagellates, Trichodesmium, coccolithophores, and dissolved nutrients, are thought to have been correlated with primary production during the study period. The measured on-deck biological data of our study allow for a general understanding of the trends in PP in the survey area of the EIO and can be incorporated into global primary production models.

Phytoplankton Primary Production and Light Attenuation Responses to the Experimental Acidification of a Small Canadian Shield Lake

1987 ◽  
Vol 44 (S1) ◽  
pp. s83-s90 ◽  
Author(s):  
J. A. Shearer ◽  
E. J. Fee ◽  
E. R. DeBruyn ◽  
D. R. DeClercq
Keyword(s):  
Primary Production ◽  
Light Attenuation ◽  
Distinct Pattern ◽  
Phytoplankton Production ◽  
Phytoplankton Primary Production ◽  
Apparent Reduction ◽  
Production Increase ◽  
Pre Treatment ◽  
Experimental Acidification ◽  
Ph Level

Phytoplankton primary production and light attenuation were monitored over a 10-yr period in Lake 223, a small, softwater, shield, lake. After 2 yr with no treatment, the lake was treated for 8 yr with sulfuric acid to decrease the epilimnetic pH from about 6.7 to 5.0. Primary production, integrated over time and depth, varied considerably during the 2 pre-treatment years. However, it increased steadily during the first 6 yr of treatment, with a total increase of more than 250%. This production increase was coincident with a decrease in epilimnetic light attenuation. After the 6th year of treatment, the production of the lake decreased although the pH level was held relatively constant during this period. Nearby control lakes tended to show a similar, though less distinct, pattern during this 10-yr period. Thus, it is difficult to separate the effects of acidification from long-term natural variation. However, there was no apparent reduction in community phytoplankton production as a consequence of the acidification and the hypothesis that acidification causes oligotrophication was not supported.

Anomalous Rainfall over Southwest Western Australia Forced by Indian Ocean Sea Surface Temperatures

2008 ◽  
Vol 21 (19) ◽  
pp. 5113-5134 ◽  
Author(s):  
Caroline C. Ummenhofer ◽  
Alexander Sen Gupta ◽  
Michael J. Pook ◽  
Matthew H. England
Keyword(s):  
Indian Ocean ◽  
Western Australia ◽  
General Circulation ◽  
Large Scale ◽  
Thermal Structure ◽  
Sea Surface ◽  
Convective Precipitation ◽  
Annual Rainfall ◽  
Significant Shift ◽  
Sst Anomalies

Abstract The potential impact of Indian Ocean sea surface temperature (SST) anomalies in modulating midlatitude precipitation across southern and western regions of Australia is assessed in a series of atmospheric general circulation model (AGCM) simulations. Two sets of AGCM integrations forced with a seasonally evolving characteristic dipole pattern in Indian Ocean SST consistent with observed “dry year” (PDRY) and “wet year” (PWET) signatures are shown to induce precipitation changes across western regions of Australia. Over Western Australia, a significant shift occurs in the winter and annual rainfall frequency with the distribution becoming skewed toward less (more) rainfall for the PDRY (PWET) SST pattern. For southwest Western Australia (SWWA), this shift primarily is due to the large-scale stable precipitation. Convective precipitation actually increases in the PDRY case over SWWA forced by local positive SST anomalies. A mechanism for the large-scale rainfall shifts is proposed, by which the SST anomalies induce a reorganization of the large-scale atmospheric circulation across the Indian Ocean basin. Thickness (1000–500 hPa) anomalies develop in the atmosphere mirroring the sign and position of the underlying SST anomalies. This leads to a weakening (strengthening) of the meridional thickness gradient and the subtropical jet during the austral winter in PDRY (PWET). The subsequent easterly offshore (westerly onshore) anomaly in the thermal wind over southern regions of Australia, along with a decrease (increase) in baroclinicity, results in the lower (higher) levels of large-scale stable precipitation. Variations in the vertical thermal structure of the atmosphere overlying the SST anomalies favor localized increased convective activity in PDRY because of differential temperature lapse rates. In contrast, enhanced widespread ascent of moist air masses associated with frontal movement in PWET accounts for a significant increase in rainfall in that ensemble set.

scholarly journals An analysis of monthly rainfall and the meteorological conditions associated with the deficient rainfall towards the end of 2017 southwest monsoon season

MAUSAM ◽  
2021 ◽  
Vol 71 (3) ◽  
pp. 391-404
Author(s):  
ARTI BANDGAR ◽  
PRABHU PALLAVI ◽  
SREEJITH O P ◽  
PAI D S
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Monsoon Season ◽  
Equatorial Indian Ocean ◽  
Longwave Radiation ◽  
Southwest Monsoon ◽  
Sst Forcing ◽  
The Indian Ocean ◽  
Neutral Conditions ◽  
Southwest Monsoon Season

This paper studies the summer monsoon 2017 and examines the number of parameters which we believe were important in understanding why monsoon failed in second half over India. The list of parameters includes monthly mean or anomalies of the following fields : sea surface temperature, outgoing longwave radiation, stream function of lower and upper atmosphere, velocity potential and monthly and seasonal precipitation. ENSO conditions were mainly neutral with warm ENSO neutral conditions observed in the first half and cool ENSO neutral conditions observed in the second half. As a result, influence on the monsoon from the large scale SST forcing from Pacific Ocean was nearly absent during the season. However, Positive IOD conditions over the Indian Ocean during the monsoon season, particularly during first half of the monsoon were prominent. The transition of warmer than normal SSTs (June and July) to normal SSTs (August) and then becoming cooler than normal SSTs (September) in the equatorial Indian Ocean had a significant influence which lead monsoon to fail in second half.   

Observations of Upper-Tropospheric Temperature Inversions in the Indian Monsoon and Their Links to Convectively Forced Quasi-Stationary Kelvin Waves

2020 ◽  
Vol 77 (8) ◽  
pp. 2835-2846 ◽  
Author(s):  
Richard Newton ◽  
William Randel
Keyword(s):  
Indian Ocean ◽  
Large Scale ◽  
Indian Monsoon ◽  
Monsoon Season ◽  
Deep Convection ◽  
Equatorial Indian Ocean ◽  
Kelvin Waves ◽  
Tropospheric Temperature ◽  
Time Behavior ◽  
Temperature Inversions

Abstract High-vertical-resolution temperature measurements from GPS radio occultation data show frequent upper-tropospheric inversions over the equatorial Indian Ocean during the summer monsoon season. Each year, around 30% of profiles in this region have temperature inversions near 15 km during the monsoon season, peaking during July–September. This work describes the space–time behavior of these inversions, and their links to transient deep convection. The Indian Ocean inversions occur episodically several times each summer, with a time scale of 1–2 weeks, and are quasi stationary or slowly eastward moving. Strong inversions are characterized by cold anomalies in the upper-troposphere (12–15 km), warm anomalies in the tropopause layer (16–18 km), and strong zonal wind anomalies that are coherent with temperature anomalies. Temperature and wind anomalies are centered over the equator and show a characteristic eastward phase tilt with height with a vertical wavelength near 5 km, consistent with a Kelvin wave structure. Composites of outgoing longwave radiation (OLR) show that strong inversions are linked to enhanced deep convection over the equatorial Indian Ocean, preceding the inversions by ~2–6 days. These characteristics suggest that the inversions are linked to convectively forced Kelvin waves, which are Doppler shifted by the easterly monsoonal winds such that they remain quasi stationary in the equatorial Indian Ocean. These large-scale waves influence circulation on the equatorial side of the Indian monsoon anticyclone; they may provide a positive feedback to the underlying convection, and are possibly linked with regions of shear-induced turbulence.

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