Understanding Insolation Through CERES Data

 

Insolation or the Incoming Solar Radiations is the main source of energy on the Earth’s Surface. The same energy is responsible for all the climatic phenomenon on the earth’s surface. It is also accountable for all the life on earth’s surface. Although, there is another fact that all the solar energy coming to the Earth’s surface is not utilized. Some of it is reflected back to space, some is absorbed by the atmosphere and some of it is absorbed by earth’s surface. There is a balance in the amount of energy reflected and absorbed which is known as the Earth-atmosphere energy balance or energy budget. To understand more about Earth’s energy budget, watch this video here.

Another important aspect about insolation is its distribution on the Earth’s surface. Due to earth’s shape, its axis tilt and rotation, all the regions doesn’t receive same amount of energy or insolation. This is the reasons for different types of climate in different regions of the world and changing seasons on Earth. We will discuss this in detail using CERES satellite imagery. 

CERES or the Clouds and Earth's Radiant Energy System is NASA’s project which provide direct measurements of solar radiation. It has been installed on many important satellites as Terra, Aqua and NOAA-20 to get Earth Radiation Budget (ERB) data at hourly, daily and monthly intervals at spatial coverage of 20 km to global level. The CERES data are used by the climate, weather and applied science researchers to address a range of researches related to   energy exchanges between the Earth and space. For more detail about CERES data, click here. The CERES data has been downloaded from here.

The satellite images used here are prepared by the FLASHFlux team, NASA Langley Research Center. FLASHFlux data are produced using CERES observations convolved with MODIS measurements from both the Terra and Aqua satellite. These colored images shows the amount of sunlight (in Watts per square meter). Light shaded areas receive more sunlight and the darkest colors show very less insolation.  

Colour Key of satellite image (From NEO Website - https://neo.sci.gsfc.nasa.gov/view.php?datasetId=CERES_INSOL_M)

Vernal Equinox (March 21^st ) – On march 21^st, the sun’s rays are directly on the equator. This is also visible from the CERES image. The brightest region is the region between Tropic of Cancer and Tropic of Capricorn. Maximum insolation is concentrated in this region. The region from the tropics to poles, shows the dark shades, where less amount of insolation is received.

In the CERES image, we can also observe the balance in the insolation received in the tropical and polar regions in both hemispheres. If we don’t consider the difference between the land and water areas, the regions beyond the tropics, in the northern and the southern hemispheres, show similar intensity of insolation. In the tropics of the northern and the southern hemispheres also, similar intensity is there. You will see later on that this is not true in the solstice. During vernal equinox, the days and night are of equal length in all parts of the world.

 

Diagram and CERES satellite imagery of Vernal Equinox

Summer Solstice (June 21^st ) – The revolving Earth around the sun in an elliptical orbit, moves to another position at summer solstice. Due to the tilt of the Earth, the distribution of insolation at this position is changed. Now, on June 21^st, the sun’s rays are directly above the tropic of Cancer in the northern hemisphere. The brightest region in CERES image i.e. the region north of tropic of Capricorn, receives the maximum insolation. While the least insolation is received in the regions south of tropic of Capricorn. Due to this unequal distribution of insolation, different seasons are experienced in northern and southern hemisphere. The different season are characterized by unequal length of day and night. As the insolation is focused on northern hemisphere, days are longer than nights. Vice versa happens in south of equator. The north of equator is summer whereas the south of equator experience winter at this time of the year. 

Diagram and CERES satellite imagery of Summer Solstice

 Autumnal Equinox (September 23^rd ) – Earth moves to another equinox position on 23^rd September. As it was in Vernal Equinox, the insolation is concentrated in between the tropic of Cancer and tropic of Capricorn. The regions beyond the tropics receive comparably less insolation, as visible in the CERES image. Likewise, the insolation intensity in northern and the southern hemispheres, roughly copies each other. Equal length of days and night are experienced on Autumnal Equinox.

Diagram and CERES satellite imagery of Autumnal Equinox

 Winter Solstice (December 21^st ) – On Winter Solstice, sun is directly above Tropic of Capricorn in South hemisphere. In the CERES image too, we can see the brightest region being the region beyond tropic of Capricorn. This region receives maximum insolation. As discussed earlier, due to unequal distribution of insolation, there is winters in the northern hemisphere and summers in the southern hemisphere. Now reverse happens, as compared to the summer solstice. There is more sunlight or insolation in south of equator, so the days are longer and nights are shorter. Vice versa happens in the Northern hemisphere.

Diagram and CERES satellite imagery of Winter Solstice

The CERES data clearly shows the amount of insolation received and shift in the incoming solar radiation seasonally. The transition of solar energy shifts can be visualized more clearly by observing the month wise imagery available on NASA’s NEO (NASA Earth Observation) website at link https://neo.sci.gsfc.nasa.gov/view.php?datasetId=CERES_INSOL_M. To know more about CERES data, click here.

 

Reference - 

NASA (n.d.). Home Page. What is CERES? Website link - https://ceres.larc.nasa.gov/

Satellite imagery produced by the NASA Earth Observations team based on FLASHFlux data. Data provided by the FLASHFlux team, NASA Langley Research Center.

NASA NEO Website (n.d.). Solar Insolation (1 Month) CERES data. Website link -- https://neo.sci.gsfc.nasa.gov/view.php?datasetId=CERES_INSOL_M).

 

Andaman and Nicobar Islands - Physiography

 

The Andaman–Nicobar Islands is an archipelago in the Bay of Bengal. The Islands is the extended part of the Arakan Yoma mountain ranges of Myanmar into the sea. The islands are known by different names like “The Islands of the Marigold sun” and “The Bay Islands”. There are about 572 islands in the Andaman and Nicobar archipelago covering the area of 8279 sq. km. But including all the Islands, smaller Islets and rocky outcrops they are 836 in number. (Andaman Government Website). The two main groups i.e. Andaman Islands and Nicobar Islands are separated by the 160 km wide Ten Degree Channel.

Andaman Islands -

In the Andaman group of Islands, the central islands have been divided into three i.e. North Andaman, Middle Andaman and South Andaman. South of these three islands there are Rutland Island followed by Little Andaman. Baratang is another main Island east of Middle Andaman Island. Ritchie’s Archipelago is another group of smaller Islands, NNE of Port Blair in Andaman Sea, including important tourist islands like Havelock, Neil and Henry Lawrence Island. These Islands are separated by passage and straits like –

Duncan Passage - Little Andaman from Great Andaman.
The Austin Strait - The Middle and North Andaman;
The Humphrey Strait - The Middle and Baratang islands;
The Middle Strait - Baratang and South Andaman;
The Macpherson Strait - The South Andaman and Rutland islands.

Nicobar Islands -

Lying south of the Andaman Islands, separated by Ten Degree Channel are the Nicobar Group of Island covering an area of 1841 km2. Moving from north to south, the main islands in the group are Car Nicobar Island in the North; followed by Katchal, Camorta, Nancowry and other smaller Islands; and Little Nicobar and Great Nicobar further south. Indira Point on the south coast of Great Nicobar Island is the southernmost point on India’s territory.

Physiography of Andaman and Nicobar Island –

Andaman Islands has most of the relief in the eastern part whereas the western part has gentle and low elevation. Great and Little Nicobar have hilly topography. The highest point in the Andaman–Nicobar Group is Saddle Peak (733 m from sea level) on North Andaman. Mount Thullier (642 m) on Great Nicobar Island is another higher peak.

Barren Island, the only active volcano of India, is an Island in Andaman Group located in Andaman Sea. Andaman Islands also have presence of Karst landscapes in the Neil Island and Baratang Island.

References – 

Bandopadhyay, Dr. P. & Carter, Andrew. (2017). Chapter 2 Introduction to the geography and geomorphology of the Andaman–Nicobar Islands. Geological Society, London, Memoirs. 47. 9-18. 10.1144/M47.2. Available at -https://www.researchgate.net/publication/313266512_Chapter_2_Introduction_to_the_geography_and_geomorphology_of_the_Andaman-Nicobar_Islands. Assessed on 25/01/2021.

Census of India 2011: Andaman and Nicobar Islands - District Census Handbook , New Delhi: Office of the Registrar General, India, 2005. Available at -https://censusindia.gov.in/2011census/dchb/3500_PART_B_DCHB_ANDAMAN%20&%20NICOBAR%20ISLANDS.pdf.

NASA/METI/AIST/Japan Space Systems, and U.S./Japan ASTER Science Team. ASTER global digital elevation model V003, 2018, distributed by NASA EOSDIS Land Processes DAAC, https://doi.org/ 10.5067/ASTER/ASTGTM. 003.