Long-term (45 years) diversified surface meteorological records from Thumba Equatorial Rocket Launching Station (TERLS), India, were collected and analysed to study the long-term changes in the overall climatology, climatology pertained to a particular observational time, mean daily climatology in temperature, inter-annual variability in temperature, interannual variability in surface pressure, and rainfall for the main Indian seasons—South West and North East monsoons and inter-annual mean monthly anomaly structure in temperature. Results on various analyses show strong and vivid features contributed by climate change for this South Peninsular Indian Arabian Sea Coastal Station, and this paper may be a first time venture which discusses climate change imparted perturbations in several meteorological parameters in different time domains, like a specific time, daily, monthly, and interannually over a station. Being a coastal rocket launching station, climatic change information is crucial for long-term planning of its facilities as well as for various rocket range operational demands.
Climate change refers to a statistically strong and significant variation in either the average state of the climate or in its variability, persisting for an extended period, typically in decades or longer. Short-period oscillations are statistically insignificant in the scenario of long-term climate change context. Climate change may be due to natural internal processes on earth (atmospheric, seismic, volcanic, and oceanic), external forces (variation in solar activity, rotation and revolution of earth), and more recently anthropogenic activities. It is now well established that anthropogenic activities cause intensification of the greenhouse effect and thereby contribute to the climate change. The paper by Oreskes [
In India, the first time document on the concern of greenhouse effect and possible mitigation measures was published in the Science Reporter, CSIR, by Ayyar [
Different data sets have been used in order to examine the monotonic change in the level of global temperature by various investigators [
In the present paper, features on surface climate change over Thumba Equatorial Rocket Launching Station (TERLS), a coastal station near the South tip of Peninsular India, are critically examined. TERLS was established as an international rocket launching station dedicated to the United Nations for conducting meteorological and sounding rocket experiments on the geomagnetic equator. Meteorology group, TERLS has one of the heaviest responsibilities in the range to cater (i) weather forecasting and data needs of sounding rocket launch operations (in planning, pad operations and launching), (ii) climatological briefing to working crews including scientists to plan experiments, (iii) Organise various met. Observations, (iv) processing, analyses, storage and retrieval of various met. data (Class I surface observatory, autoweather stations, sonic anemometers, 50 m micro meteorological flux tower facility, meteorological balloon launches, rocket chaff derived wind data) and provide the data for users demand. For the planning of a scientific mission, the variability of climate is very crucial and thereby the importance of the present study on the climate change perspective. Importance of weather factors affecting rocket operations can be found elsewhere in detail [
A class I surface meteorological observatory was established at TERLS (8°32′′N/76° 52′′E, 6.7 amsl) by India Meteorological Department (IMD) approximately 70 m away from the coastline of the Arabian Sea coast (Figure
Details on instrumentation, data used, and the observed variation in maximum absolute error in monthly mean used in the discussion of climatology at 0830 IST.
S. no | Parameter | Data used | Instrument | Height (agl) (cm) | Exposure | Lowest and highest maximum absolute error | Make | Maintenance and calibration protocol |
---|---|---|---|---|---|---|---|---|
1 | Maximum temperature (°C) | 1964–2008 | Maximum thermometer (Mercury-in-glass thermometer) | 122 | Stevenson screen | 0.087 to 0.132 (°C) | IMD | Daily, weekly, monthly, half yearly, annual, and periodic |
2 | Minimum temperature (°C) | 1964–2008 | Minimum thermometer (spirit-in-glass) | 122 | Stevenson screen | 0.061 to 0.145 (°C) | IMD | |
3 | Dry-bulb temperature (°C) | 1964–2008 | Drybulb thermometer (mercury-in-glass thermometer) | 122 | Stevenson screen | 0.088 to 0.125 (°C) | IMD | |
4 | Rainfall (mm) | Nonrecording rain gauge of collector area 20 square cm |
0 | Ground | ||||
4 | Wet-bulb temperature (°C) | 1964–2008 | Wet-bulb thermometer | 122 | Stevenson screen | 0.06 to 0.146 (°C) | IMD | |
5 | Relative humidity (%) | 1964–2008 | Drybulb thermometer, wetbulb thermometer, and psychrometer table. | 122 | Stevenson screen | 0.512 to 0.916 (%) | IMD | |
6 | Soil temperature (°C) | 1964–2008 | Soil thermometer in metallic tube | −5 | 0.201 to 0.261 (°C) | IMD | ||
7 | Pressure (mb) | 1974–2008 | Aneroid barograph (diaphragm type) | 6.70 m amsl | IMD | |||
8 | Wind speed |
1964–2008 | Anemometer | 300 | 0.043 to 0.24 (m/s) | IMD/Dynalab | ||
9 | Wind direction |
1964–2008 | Wind vane | 300 | Within 1 degree | IMD/Dynalab |
Location shows the class-I surface meteorological observatory at Thumba.
The above mentioned 45 years of data have partitioned into two climatological slots of 30 years each, namely, 1964 to 1993 and from 1979 to 2008, respectively, called as past data for the former and present data for the later. Maximum absolute error values in the total data set (1962–2008) are the summation of errors [
Maximum temperature, minimum temperature, and 24 hr accumulated rainfall are the only 3 meteorological parameters registered at 0830 IST having effect of the past 24 hr variability behaviour. Climatology for various parameters has been derived for past data and present data and presented in Tables
Climatology and Δ of maximum temperature, minimum temperature, mean daily temperature, mean range in temperature, and monthly rainfall.
Month | Maximum temperature °C | Minimum temperature °C | Mean daily temperature °C | Mean range in temperature °C | Monthly rainfall mm | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | |
JAN | 32.59 | 32.76 | +0.17 | 21.30 | 21.58 | +0.28 | 26.94 | 27.16 | +0.22 | 11.29 | 11.17 | −0.12 | 11.80 | 11.10 | −0.70 |
FEB | 33.12 | 33.32 | +0.20 | 21.89 | 22.42 | +0.53 | 27.51 | 27.87 | +0.36 | 11.24 | 10.91 | −0.33 | 16.20 | 16.40 | +0.20 |
MAR | 33.84 | 34.07 | +0.23 | 23.75 | 24.13 | +0.38 | 28.78 | 29.09 | +0.31 | 10.06 | 9.92 | −0.14 | 33.20 | 34.80 | +1.60 |
APR | 34.25 | 34.41 | +0.16 | 25.24 | 25.51 | +0.27 | 29.76 | 29.95 | +0.19 | 9.05 | 8.88 | −0.17 | 104.10 | 99.40 | −4.70 |
MAY | 33.03 | 33.46 | +0.43 | 25.14 | 25.50 | +0.36 | 29.12 | 29.48 | +0.36 | 7.97 | 7.96 | −0.01 | 179.20 | 165.80 | −13.40 |
JUN | 30.36 | 30.71 | +0.35 | 23.99 | 24.36 | +0.37 | 27.20 | 27.53 | +0.33 | 6.43 | 6.35 | −0.08 | 292.70 | 272.20 | −20.50 |
JUL | 29.38 | 29.48 | +0.10 | 23.36 | 23.79 | +0.43 | 26.38 | 26.63 | +0.25 | 6.03 | 5.68 | −0.35 | 203.00 | 181.30 | −21.70 |
AUG | 29.27 | 29.60 | +0.33 | 23.39 | 23.80 | +0.41 | 26.35 | 26.70 | +0.35 | 5.92 | 5.79 | −0.13 | 141.50 | 120.90 | −20.60 |
SEP | 30.34 | 30.70 | +0.36 | 23.68 | 24.00 | +0.32 | 27.04 | 27.34 | +0.30 | 6.71 | 6.67 | −0.04 | 158.20 | 171.00 | +12.80 |
OCT | 31.19 | 31.53 | +0.34 | 23.74 | 24.04 | +0.30 | 27.50 | 27.76 | +0.26 | 7.53 | 7.44 | −0.09 | 204.90 | 241.40 | +36.50 |
NOV | 31.76 | 31.77 | +0.01 | 23.21 | 23.57 | +0.36 | 27.48 | 27.67 | +0.19 | 8.53 | 8.20 | −0.33 | 166.80 | 170.70 | +3.90 |
DEC | 32.30 | 32.56 | +0.26 | 22.44 | 22.44 | +0.00 | 27.35 | 27.50 | +0.15 | 9.83 | 10.11 | +0.28 | 66.60 | 53.70 | −12.90 |
DEC, JAN, and FEB: winter; MAR, APR, and MAY: summer; JUN, JUL, AUG, and SEP: SW monsoon; OCT, NOV: NE monsoon.
Climatology and Δ of dry-bulb temperature, wet bulb temperature, dew point temperature, relative humidity, and soil temperature.
Month |
Dry-bulb temperature |
Wet-bulb temperature |
Dew point temperature |
Relative humidity (%) |
Soil temperature | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | |
JAN | 26.06 | 27.07 | +1.01 | 22.33 | 22.90 | +0.57 | 20.35 | 20.69 | +0.34 | 71.36 | 68.85 | −2.51 | 29.03 | 31.38 | +2.35 |
FEB | 26.77 | 27.71 | +0.94 | 23.04 | 23.55 | +0.51 | 21.12 | 21.43 | +0.31 | 71.76 | 69.41 | −2.35 | 30.41 | 32.54 | +2.13 |
MAR | 28.31 | 29.20 | +0.89 | 24.58 | 24.94 | +0.36 | 22.81 | 22.94 | +0.13 | 72.55 | 69.53 | −3.02 | 32.80 | 34.25 | +1.45 |
APR | 29.29 | 30.00 | +0.71 | 26.09 | 26.30 | +0.21 | 24.71 | 24.72 | +0.01 | 76.56 | 73.61 | −2.95 | 33.73 | 35.11 | +1.38 |
MAY | 28.70 | 29.43 | +0.73 | 26.12 | 26.43 | +0.31 | 25.02 | 25.17 | +0.15 | 80.94 | 78.33 | −2.61 | 32.46 | 34.16 | +1.70 |
JUN | 26.61 | 27.33 | +0.72 | 25.20 | 25.57 | +0.37 | 24.55 | 24.81 | +0.26 | 88.51 | 86.43 | −2.08 | 29.55 | 30.99 | +1.44 |
JUL | 25.76 | 26.36 | +0.60 | 24.55 | 24.88 | +0.33 | 23.95 | 24.21 | +0.26 | 89.80 | 88.03 | −1.77 | 29.01 | 30.00 | +0.99 |
AUG | 25.90 | 26.60 | +0.70 | 24.60 | 24.96 | +0.36 | 23.97 | 24.22 | +0.25 | 89.40 | 86.98 | −2.42 | 29.60 | 30.96 | +1.36 |
SEP | 26.62 | 27.37 | +0.75 | 24.84 | 25.21 | +0.37 | 24.02 | 24.25 | +0.23 | 85.77 | 83.45 | −2.32 | 31.10 | 32.23 | +1.13 |
OCT | 26.81 | 27.59 | +0.78 | 24.90 | 25.33 | +0.43 | 24.02 | 24.32 | +0.30 | 85.01 | 82.61 | −2.40 | 31.40 | 32.45 | +1.05 |
NOV | 26.90 | 27.63 | +0.73 | 24.40 | 24.86 | +0.46 | 23.27 | 23.58 | +0.31 | 80.84 | 79.35 | −1.49 | 30.99 | 32.02 | +1.03 |
DEC | 26.70 | 27.59 | +0.89 | 23.35 | 23.72 | +0.37 | 21.61 | 21.74 | +0.13 | 74.48 | 71.39 | −3.09 | 30.52 | 32.09 | +1.57 |
DEC, JAN, and FEB: winter; MAR, APR, and MAY: summer; JUN, JUL, AUG, and SEP: SW monsoon; OCT, NOV: NE monsoon.
Climatology and Δ of visibility code, low cloud, high cloud, and total cloud.
Month | Visibility code (0830 IST) | Low cloud (0830 IST) | Middle cloud (0830 IST) | High cloud (0830 IST) | Total cloud (0830 IST) | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | |
JAN | 96.79 | 96.98 | +0.19 | 0.55 | 0.47 | −0.08 | 0.81 | 0.78 | −0.03 | 1.18 | 1.35 | +0.17 | 2.51 | 2.53 | +0.02 |
FEB | 96.75 | 96.91 | +0.16 | 0.48 | 0.47 | −0.01 | 0.66 | 0.58 | −0.08 | 1.08 | 1.16 | +0.08 | 2.21 | 2.17 | −0.04 |
MAR | 96.61 | 96.88 | +0.27 | 0.62 | 0.71 | +0.09 | 0.54 | 0.37 | −0.17 | 1.06 | 1.21 | +0.15 | 2.20 | 2.24 | +0.04 |
APR | 96.77 | 96.86 | +0.09 | 1.25 | 1.57 | +0.32 | 1.00 | 0.87 | −0.13 | 1.72 | 1.79 | +0.07 | 3.91 | 3.94 | +0.03 |
MAY | 96.70 | 96.68 | −0.02 | 2.02 | 2.08 | +0.06 | 1.45 | 1.43 | −0.02 | 1.56 | 1.64 | +0.08 | 4.87 | 4.68 | −0.19 |
JUN | 96.26 | 96.43 | +0.17 | 2.86 | 2.84 | −0.02 | 2.31 | 2.37 | +0.06 | 1.16 | 1.49 | +0.33 | 5.96 | 5.90 | −0.06 |
JUL | 96.10 | 96.37 | +0.27 | 2.74 | 2.74 | +0.00 | 2.50 | 2.82 | +0.32 | 1.26 | 1.67 | +0.41 | 5.96 | 6.06 | +0.10 |
AUG | 96.41 | 96.58 | +0.17 | 2.27 | 2.38 | +0.11 | 2.31 | 2.28 | −0.03 | 1.31 | 1.86 | +0.55 | 5.63 | 5.68 | +0.05 |
SEP | 96.48 | 96.63 | +0.15 | 2.16 | 2.15 | −0.01 | 1.63 | 1.62 | −0.01 | 1.34 | 1.62 | +0.28 | 4.93 | 4.90 | −0.03 |
OCT | 96.76 | 96.70 | −0.06 | 1.75 | 1.96 | +0.21 | 2.07 | 2.14 | +0.07 | 1.29 | 1.73 | +0.44 | 4.92 | 5.06 | +0.14 |
NOV | 96.68 | 96.65 | −0.03 | 1.44 | 1.55 | +0.11 | 1.86 | 1.94 | +0.08 | 1.26 | 1.72 | +0.46 | 4.40 | 4.65 | +0.25 |
DEC | 96.81 | 96.79 | −0.02 | 1.01 | 0.91 | −0.10 | 1.40 | 1.15 | −0.25 | 1.20 | 1.40 | +0.20 | 3.56 | 3.25 | −0.31 |
DEC, JAN, and FEB: winter; MAR, APR, and MAY: summer; JUN, JUL, AUG, and SEP: SW monsoon; OCT, NOV: NE monsoon.
Climatology and Δ of wind speed (scalar), wind speed (resultant), and wind steadiness factor.
Month |
Wind speed (scalar) |
Wind speed (resultant) |
Wind steadiness factor | ||||||
---|---|---|---|---|---|---|---|---|---|
1964–1993 | 1979–2008 | Δ | 1979–2008 | Δ | 1964–1993 | 1979–2008 | Δ | ||
JAN | 1.04 | 0.75 | −0.29 | 0.71 | 0.33 | −0.38 | 68.89 | 44.48 | −24.41 |
FEB | 1.07 | 0.81 | −0.26 | 0.73 | 0.38 | −0.35 | 67.95 | 47.36 | −20.59 |
MAR | 1.21 | 1.00 | −0.21 | 0.83 | 0.56 | −0.27 | 68.49 | 56.15 | −12.34 |
APR | 1.29 | 1.00 | −0.29 | 0.92 | 0.63 | −0.29 | 71.46 | 63.15 | −8.31 |
MAY | 1.45 | 1.04 | −0.41 | 1.14 | 0.75 | −0.39 | 78.40 | 72.44 | −5.96 |
JUN | 1.49 | 1.09 | −0.40 | 1.03 | 0.8 | −0.23 | 68.97 | 73.65 | +4.68 |
JUL | 1.68 | 1.35 | −0.33 | 1.15 | 0.94 | −0.21 | 68.08 | 69.60 | +1.52 |
AUG | 1.61 | 1.31 | −0.30 | 1.36 | 1.05 | −0.31 | 84.68 | 79.99 | −4.69 |
SEP | 1.57 | 1.10 | −0.47 | 1.17 | 0.81 | −0.36 | 74.57 | 74.06 | −0.51 |
OCT | 1.10 | 0.82 | −0.28 | 0.64 | 0.40 | −0.24 | 58.69 | 49.26 | −9.43 |
NOV | 0.97 | 0.74 | −0.23 | 0.49 | 0.23 | −0.26 | 50.29 | 31.17 | −19.12 |
DEC | 1.01 | 0.75 | −0.26 | 0.67 | 0.37 | −0.30 | 66.44 | 48.88 | −17.56 |
DEC, JAN, and FEB: winter; MAR, APR, and MAY: summer; JUN, JUL, AUG, and SEP: SW monsoon; OCT, NOV: NE monsoon.
From each individual daily maximum and minimum temperature, mean daily temperatures ((maximum temperature + minimum temperature)/2) are computed and further derive the past data and present data climatologies of mean temperatures. Only positive Δ values are observed throughout the year, which clearly indicate that the temperature over this tropical coastal station is increasing. Temperature climatologies have shown the tropical monsoonal characteristic of two maxima and two minima in monthly variation.
The diurnal temperature range is calculated from individual maximum and minimum temperature value and calculated past data and present data temperature range climatologies. Range climatologies are featured by annual variation. The prominent feature of negative Δ values in range is seen, which shows that the difference between maximum temperature and minimum temperature in a day is decreasing. Also, the larger rate of increase in minimum temperatures than maximum temperatures results in these negative Δ values in the diurnal temperature range.
The rainfall Δ shows decrease in rainfall in present data for the summer months April and May. Well-marked negative Δ values of about 21 mm are observed in the SW monsoon months (June–August). An increase in rainfall activity is detected in the SW monsoon month September and in the NE monsoon months October and November (debted to monsoonal climate) with maximum value of +36.50 mm in October. The station weather is dominated by convective mesoscale systems during the NE monsoon. Probably this investigation poses the doubt about whether such meso-scale weather phenomena like thunderstorm formations are on increasing trend during NE Monsoon and thereby an increase in Δ.
Analyses are carried out on different parameters collected at 0830 IST. Δ in dry bulb temperature, wet bulb temperature, and dew point temperature obtained from the two climatologies show only positive values. It ranges from +0.60°C in July to +1.01°C in January for dry bulb temperature. Variations in Δ among the SW monsoon months are less in general for all the above three variables, even though a maximum value in Δ is observed in dry bulb temperature. The less variation of wet bulb and dew point temperatures may be as a result of moisture laden atmosphere during the period which imparts corresponding variations in the moisture parameters like wet bulb temperature and dew point temperature.
Station relative humidity values at 0830 IST show more than 70% throughout the year with maximum in SW monsoon of the order 89%. Low negative values in Δ relative humidity are detected as the air becomes drier in present data compared to past. As the air is getting dried, both dew point and the wet bulb temperatures are supposed to show negative Δ values, but the feature is not detected. This may be inferred as the dry bulb temperature is the key parameter in elevating Δ values of both dew point and wet bulb temperatures, and the meagre relative humidity decrease in present data than past data is insignificant to impart Δ changes in dew point and wet bulb temperatures. Climatologies of RH also have shown two maxima and two minima, whereas the secondary minima around the NE monsoon is shallow in character.
Significant positive Δ values are observed among the two climatologies in soil temperature with a low value of +0.99°C to a high of +2.35°C in July and January, respectively. Perhaps the Δ increase observed in the winter months January and February may contribute reduction in radiational cooling which leads to a reduction in fog formation probability over the station. Soil temperature climatologies also have shown tropical monsoonal type with two maxima and minima.
Wind speed (both scalar and resultant) is decreased in present climatologies. Mathematically resultant wind speed shall be determined as the square root of the sum of the squares of zonal and meridional wind components. The encountered Δ values that rise to a maximum value of the order 0.5 m/s are due to decrease in wind speeds in the present data climatology in comparison with past data climatology. Wind steadiness factor values at 0830 IST are computed as the ratio of mean resultant wind speed to mean scalar wind (average value of scalar wind speeds) expressed in %, and the two slot climatologies are made. Wind steadiness factor is a general meteorological technique in order to derive the quantitative estimate of steadiness of wind direction [
Visibility and cloud climatologies are also studied. As these observational procedures are non-instrumental, the data is too subjective and quality observation is solely vested on the experience of the weather observer. The observation shows, better visibility codes in the present data climatology. A visibility code of 96 and above signifies that a well-defined object (like a mobile phone tower) at least 1 km far can be distinctly differentiable. Among various cloud climatology, dominant positive Δ values are existed in high clouds through out the year which may be pointed out as one of the reason for subdued albedo effect which enhances greenhouse effect, and hereby surface temperature escalation. This may be the result of number of high cloud types (Ci and Cc) are less compared to the varieties of low and middle cloud types, which enables easy estimation for the observer while making counts on high clouds. The increase in high cloud climatology values in present data may be the result of increase in air traffic resulted contrails over the region which results an increase in cirrus cloud formations due to tropical dynamics unlike microphysical processes in mid-latitudes as in Minnis et al. [
Mean of daily maximum, minimum, mean and range in temperature between daily maximum and minimum temperatures are computed and depicted for the 365 days in a year (Figures
(a) Mean daily temperature climatologies in 1964–1993, 1979–2008, and their differences, along with (b) standard deviation of corresponding climatologies.
(a) Mean daily temperature range climatologies in 1964–1993, 1979–2008, and their differences, along with (b) standard deviation of corresponding climatologies.
(a) Maximum daily temperature climatologies in 1964–1993, 1979–2008, and their differences, along with (b) standard deviation of corresponding climatologies.
(a) Minimum daily temperature climatologies in 1964–1993, 1979–2008, and their differences, along with (b) standard deviation of corresponding climatologies.
Difference statistics for 365 days between present data and past data on daily maximum, minimum, mean temperatures, and range in temperature within a day.
Inter annual variability has critically examined for annual mean of minimum, maximum and mean temperatures, annual rainfall in the SW and NE monsoon over the station and for the Kerala State and average annual surface pressure in the SW and NE monsoons for the station. Each inter annual variability data has undergone an 11 year moving average with end point extrapolation till the raw data availability to bring out long term trend and the trend line also has shown in each inter annual variability figures similar to Krishnakumar et al. [
Linear trends of 11 year moving averaged data on various inter-annual variability. Level of significance was choosen at 0.05% to read out critical
No. | Interannual variability in |
|
Slope ( |
Calculated |
|
Comments | Data missing |
---|---|---|---|---|---|---|---|
1 | Mean temperature | 0.891 |
|
12.08154 | 38 | Strong and significant. (Figures |
1974, 1975, 1976, 1982, and 1992 |
2 | Mean maximum temperature | 0.725 |
|
6.50392 | 38 | Strong and significant. |
1974, 1975, 1976, 1982, and 1992 |
3 | Mean minimum temperature | 0.952 |
|
19.29677 | 38 | Strong and significant. |
1974, 1975, 1976, 1982, and 1992 |
4 | Mean temperature range | −0.190 |
|
−1.19078 | 38 | Weak and not significant (Figure |
1974, 1975, 1976, 1982, and 1992 |
5 | South West monsoon rainfall (Thumba) | −0.477 |
|
−3.483 | 41 | Weak and significant (Figure |
1964, 1998 |
6 | North East monsoon rainfall (Thumba) | 0.848 |
|
10.000 | 39 | Strong and significant (Figure |
1964, 1977, 1992, and 1998 |
7 | South West monsoon rainfall (Kerala) | −0.721 |
|
−6.587 | 40 | Strong and significant (Figure |
1964, 2007, and 2008 |
8 | North East monsoon rainfall (Kerala) | 0.737 |
|
6.986 | 41 | Strong and significant (Figure |
1964, 2008 |
9 | South West monsoon surface pressure | 0.445 |
|
2.899 | 34 | Weak and significant (Figure |
1964 to 1972 |
10 | North East monsoon surface pressure | −0.616 |
|
−4.555 | 34 | Strong and significant (Figure |
1964 to 1972 |
To assess the interannual variability with temperature, annual mean minimum, mean maximum and mean of mean temperatures are found out for each year from 1964 to 2008. Also to ascertain deviation from the normal, each yearly mean value is deducted from the mean of the entire values available for present data and thereby extracted the anomaly in temperature. Mean and standard deviation of daily mean, maximum, minimum and daily temperature range are computed for a year and depicted in Figures
(a) Yearly mean temperature along with standard deviation and (b) anomaly.
(a) Yearly mean maximum temperature along with standard deviation and (b) anomaly.
(a) Yearly mean minimum temperature along with standard deviation and (b) anomaly.
(a) Yearly mean temperature range along with standard deviation and (b) anomaly.
Mean monthly anomaly structures in minimum, maximum, and mean temperatures are presented in time section contour diagrams (Figures
Maximum temperature anomaly.
Minimum temperature anomaly.
Mean temperature anomaly.
Interannual variability in rainfall and surface pressure particularly for SW monsoon and NE monsoon are studied. A decrease in trend in SW monsoon and an increase in trend in NE monsoons are the observed features over the station with decadal variability of (−
South West monsoon rainfall over Thumba.
North East monsoon rainfall over Thumba.
South West monsoon rainfall over Kerala.
North East monsoon rainfall over Kerala.
Interannual variability in surface pressure was derived and depicted for SW monsoon (Figure
(a) Interannual variability in surface pressure for South West monsoon season along with (b) standard deviation and number of observations.
(a) Interannual variability in surface pressure for North East monsoon season along with (b) standard deviation and number of observations.
Long-term surface meteorological records from TERLS were collected and analysed to study the long-term changes in overall climatology, climatology pertained to a particular time of observation, mean daily climatology in temperature, interannual variability in temperature, interannual variability in SW and NE monsoon rainfall, and mean monthly anomaly structure in temperature. Results on various analyses show strong and vivid features contributed by climate change. The salient features observed contributed by climate change are as follows: All the temperatures show increase in their behaviour with slight decrease in RH between the present climatology and past climatology. Steadiness of wind decreases especially in non-SW monsoon months, which gives an indirect signature of possible modifications in meso-scale systems. High cloud climatology increases and thereby probable modifications in radiation budget, time of occurrence of maximum and minimum temperatures. Daily statistics for 365 days show more than 80% exceedance in present climatology in comparison to past in minimum, maximum, and mean temperature. Interannual variability analysis in mean temperature for this tropical coastal station shows +1.3°C/100 years which is same as that of global ocean rate. Observed interannual rainfall variability in SW monsoon and North East monsoon shows decrease in trend by –21.45 mm/decade and increase in trend by +39.3 mm/decade, respectively. Prognosis on this observation points out the likelihood exceedance of NE monsoon rainfall over the South West monsoon after the year 2050 for the station. But it is prejudicial to infer that the rainfall increase in NE monsoon can compensate the forecasted decrease in SW monsoon, since NE monsoon is mostly of heavy rainfall in nature as a result of meso-scale convective systems. Such rainfall runoff is very fast than the slow water infiltration feature in association with SW monsoon rainfall, which is essential for irrigation and agricultural needs. Decadal variability in surface pressure has shown +0.06 mb and −0.10 mb for SW monsoon and NE monsoon, respectively.
The imprints due to climate change on various meteorological parameters over this coastal station proved that the region also faces vulnerable situation due to the phenomena, and therefore, necessary engineering methods/socioeconomic steps are to be undertaken.
The availability of this unique data for a continuous period of 45 years is the outcome of concerted and whole hearted efforts put in by the staffs of TERLS/India Meteorological Department. It is a pleasure to acknowledge with esteemed gratitude the team that worked since 1963 at the TERLS, Thumba, whose efforts have yielded the voluminous unique data bank which is available for investigations. The authors are extremely grateful to Dr. K Krishnamoorthy, Director, Space Physics Laboratory, VSSC, and the reviewers for their valuable comments that helped to improve the paper to the final form.